Published online before print October 10, 2005, doi: 10.1161/01.HYP.0000186278.50275.fa
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(Hypertension. 2005;46:1154.)
© 2005 American Heart Association, Inc.
Original Articles |
Activation of Vascular BK Channel by Tempol in DOCA-Salt Hypertensive Rats
From the Department of Pharmacology and Toxicology, Michigan State University, East Lansing.
Correspondence to Hui Xu, MD, PhD, Department of Pharmacology and Toxicology, Michigan State University, East Lansing, MI 48824. E-mail xuhui2{at}msu.edu
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Abstract |
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Large-conductance Ca2+-activated potassium (BK) channels modulate vascular smooth muscle tone. Tempol, a superoxide dismutase (SOD) mimetic, lowers blood pressure and inhibits sympathetic nerve activity in normotensive and hypertensive rats. In the present study, we tested the hypotheses depressor responses caused by tempol are partly mediated by vasodilation. It was found that tempol, but not tiron (a superoxide scavenger), dose-dependently relaxed mesenteric arteries (MA) in anesthetized sham and deoxycorticosterone acetate (DOCA)-salt hypertensive rats. Tempol also reduced perfusion pressure in isolated, norepinephrine (NE) preconstricted MA from sham and DOCA-salt hypertensive rats. Maximal responses in DOCA-salt rats were twice as large as those in sham rats. The vasodilation caused by tempol was blocked by iberiotoxin (IBTX, BK channel antagonist, 0.1 µmol/L) and tetraethylammonium chloride (TEA) (1 mmol/L). Tempol did not relax KCl preconstricted arteries in sham or DOCA-salt rats, and N
-nitro-L-arginine methyl ester (L-NAME), apamin, or glibenclamide did not alter tempol-induced vasodilation. IBTX constricted MA and this response was larger in DOCA-salt compared with sham rats. Western blots and immunohistochemical analysis revealed increased expression of BK channel 
subunit protein in DOCA-salt arteries compared with sham arteries. Whole-cell patch clamp studies revealed that tempol enhanced BK channel currents in HEK-293 cells transiently transfected with mslo, the murine BK channel a subunit. These currents were blocked by IBTX. The data indicate that tempol activates BK channels and this effect contributes to depressor responses caused by tempol. Upregulation of the BK channel subunit contributes to the enhanced depressor response caused by tempol in DOCA-salt hypertension.
Key Words: antioxidants • hypertension • vasodilation
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Introduction |
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Superoxide anion (O2–) increases blood pressure in hypertensive animals and humans in part by reducing the vascular bioavailability of nitric oxide (NO).1 4-Hydroxy 2,2,6,6,-tetramethyl piperidine 1-oxyl (tempol), a superoxide dismutase (SOD) mimetic, lowers blood pressure in normotensive and hypertensive rats by multiple mechanisms.2–5 Acute tempol treatment of normotensive, DOCA-salt and spontaneously hypertensive rats (SHRs) inhibits sympathetic nerve activity and this effect is not prevented by nitric oxide synthase (NOS) inhibition.2–6 Local application of tempol onto renal sympathetic nerves decreased nerve activity without changing blood pressure (BP) or heart rate (HR).7 The results suggested that changes in K+ channel activity might contribute to sympatho-inhibition caused by tempol. Central administration of tempol in normotensive rats reduced sympathetic nerve discharge8,9 and attenuated sympathetic excitation caused by central angiotensin II administration.9 Therefore, it is possible that tempol-induced vasodilation in vivo is masked by its sympatho-inhibitory effects.9
Chronic tempol treatment attenuates blood pressure increases in hypertensive animals, an effect attributed to improvement in endothelium function and/or a reduction of oxidative stress.10,11 However, data obtained in salt-induced or corticotropin (ACTH)-induced hypertension in rats indicate tempol-induced depressor effects are independent of endothelial function and oxidative stress.12–15 Therefore, tempol-induced depressor effects may not be caused entirely by removal of O2– and/or increased NO availability.
The present studies were performed to determine whether tempol directly causes vasodilation via an increased NO availability in DOCA-salt hypertensive rats. Furthermore, the role of K+ channel activation in tempol-induced vasodilation was also studied. Finally, the effects of tempol on BK channels were determined by whole cell patch clamp in HEK-293 cells transfected with mslo, the mouse BK channel subunit.
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Materials and Methods |
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Animals
Animal use protocols were approved by the All University Committee for Animal Use and Care at Michigan State University. Sham operated and DOCA-salt hypertensive rats (male, 170 to 225 grams; Charles River Laboratories) were prepared as previously described.2,6 Blood pressure was measured in conscious animals by tail-cuff plethysmography 4 weeks after DOCA implantation.
In Situ Measurement of Mesenteric Artery Diameter in Anesthetized Rats
HR, BP, and mean arterial blood pressure (MAP) were recorded as reported.2,4,6 An ileal loop was drawn out and fixed to a silatic chamber perfused with Krebs solution (37°C). The Krebs solution contains (mmol/L): NaCl 118, KCl 4.7, MgCl2 1.1, NaH2PO4 1.2, CaCl2 2.5, NaHCO3 25, glucose 11, equilibrated with compressed air (5% CO2-21% O2-74% N2). Mesenteric artery (MA; outer diameter [OD] &250 µm) was isolated and cleared. The output of a black–white video camera (DAGE-MTI 100) attached to a microscope (Nikon SMZ 1000) was fed to a frame grabber card (Picolo, Euresys Inc) mounted in a personal computer. Video images were analyzed using Diamtrak software (Diamtrak). The digitized signal was converted to an analog output (NuDAQ +6208, ADLINK Tech Inc). Analog signals for HR, BP, MAP, and MA-OD were digitized (Digidata 1200; Axon Instruments) and displayed using pClamp 7.0 (Axon Instruments).
Measurement of Perfusion Pressure in Isolated, Perfused MA In Vitro
The mesenteric bed was removed from rats and the superior MA was cannulated, placed in a chamber superfused with Krebs’ solution (37°C). The arterial tree was perfused with Krebs’ solution (&4 mL/min). The flow rate was adjusted to keep mean arterial perfusion pressure (MAPP) at 30 to 40 mm Hg in sham and DOCA-salt MA in the absence of drugs. MAPP was monitored with a Statham pressure transducer and a strain gauge amplifier (CP122, Grass Instruments). Data were displayed and analyzed using Polyview software (Grass Instruments).
Analysis of Vascular BK Channel Subunit Expression
Protein isolation from aorta and MA were described previously.16 Equivalent amounts of aorta and MA protein (100 µg) from sham and DOCA-salt rats were separated on 7% SDS-polyacrylamide gels and transferred to Immobilon-P membranes for Western analyses using anti-Kca2+ 1.1 (1:500; Alomone Labs Ltd, Jerusalem, Israel) antibody. Smooth muscle -actin (1:5000; Oncogene) was used to normalize measurements of BK channel protein.
Vascular smooth muscle cells (VSMCs) from MA were isolated as described.17 Cells were fixed immediately using Zamboni’s fixative (2% (V/V) formaldehyde and 0.2% (V/V) picric acid in 0.1 mol/L phosphate-buffered saline), and incubated with rabbit anti-KCa2+ 1.1 antibody (1:400; Alomone Labs.) and goat anti-rabbit IgG conjugated to Cy3 (1:200; Jackson ImmunoResearch) as well as 4', 6-diamidino-2-phenylindole (DAPI; 10 µg/mL; Sigma). In some experiments, primary antibody was pre-incubated with a 5-fold excess of the antigen competing peptide. Images were obtained using a fluorescence microscope (Nikon, TE 2000-U) and processed using Metaimaging Series 6.1 and Adobe Photoshop 8.0.
Expression of BK Channel A-Subunits (mslo) in HEK-293 Cells
The BK channel mslo -subunit cDNA plasmid (in the expression vector pcDNA3Zeo, Invitrogen) was a gift from Dr Christopher Lingle, (Department of Anesthesiology, Washington University, St. Louis, Mo). HEK-293 cells were cultured in Dulbecco’s F-12 medium (Invitrogen) supplemented with 10% FCS (Sigma) and 2 mmol/L glutamine (Invitrogen). Cells were transfected with 2 µg of mslo plasmid and green fluorescence protein (GFP) (0.1 µg) using Lipofectamine 2000 (Invitrogen). Transfection efficiency was &20%. Control cells were transfected with GFP only.
Whole-Cell Recording of BK Channel Currents
Whole-cell current recordings were performed between 1 and 4 days after transfection. The bath solution contained (mmol/L): NaCl 117, KCl 4.7, CaCl2 2.5, MgCl2 1.2, NaH2PO4 1.2, NaHCO3 25, and glucose 11. The pipette solution contained: NaCl 8, KCl 50, CaCl2 0.826 (free Ca2+ 200 nmol/L), MgCl2 1, HEPES 10, KAsp 70, HEDTA 1, ATP 2 (Mg salt), and GTP 0.1 (Na salt). In some experiments, the HEDTA in the pipette solution was increased to 10 mmol/L, which reduced Ca2+ to 5 nmol/L. Free Ca2+ levels were calculated using Sliders software (http://www.stanford.edu/&cpatton/maxc.html). The cell was held at –70 mV and depolarized with a series 200-ms step commands to +80 mV in 10-mV increments at 15-seconds intervals. All recordings were made using an Axopatch 200A amplifier (Axon Instruments). Data were acquired using pClamp 6.0 (Axon Instruments)
Drugs
Tempol, IBTX, apamin, TEA and tiron were purchased from Sigma Chemical Co. Glibenclamide was purchased from TOCRIS.
Statistics
Paired and unpaired t tests were used to make single point comparisons. Comparison of multiple points generated in dose-response curves were tested by 2-way ANOVA with repeated measures, followed by Duncan’s multiple range test. Significance was accepted at P<0.05.
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Results |
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In anesthetized rats, MAP was 160±5 mm Hg in DOCA-salt (n=8), and 110±4 mm Hg in sham rats (n=8) (P<0.05). HR in DOCA-salt rats did not differ from sham rats. Average systolic blood pressure was 195±4 mm Hg in DOCA-salt (n=44) and 120±5 mm Hg in sham rats (n=43) (P<0.05) in vitro studies. The body weight of sham rats was 420±8 grams and 320±7 grams in DOCA-salt rats (P<0.05).
Tempol Relaxed MA In Situ in Anesthetized Sham and DOCA-Salt Rats
Tempol was applied by superfusion cumulatively (0.001 to 3 mmol/L). The resting MA-OD in DOCA-salt rats did not differ from sham rats (265±20 µm, n=4, versus 270±15 µm, n=4; P>0.05). Tempol increased MA-OD without changing HR or MAP (Figure 1A and 1B). Dose-response curves in DOCA-salt rats were left-shifted (Figure 1C). The EC50 for tempol was 40±8 µmol/L in DOCA-salt, and 170±12 µmol/L in sham rats (P<0.05). The maximal response was larger in DOCA-salt MA (31±4% versus 19±5%), but this did not reach statistical significance (P=0.057) (Figure 1C).
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Topical L-NAME treatment (0.3 mmol/L; 20 minutes) decreased MA-OD by 10% in sham and 5% in DOCA-salt rats without changing HR or MAP. L-NAME inhibited vasodilation caused by ACh (0.1 µmol/L) by >70% without changing SNP (0.1 µmol/L) responses in sham or DOCA-salt MA (not shown). L-NAME treatment did not affect the vasodilation caused by tempol in sham or DOCA-salt rats (Figure 1C).
Tempol, But Not Tiron, Reduced MAPP in Isolated Perfused MA
MAPP increased to 120±15 mm Hg by NE (1 to 2 µmol/L) and 120±13 mm Hg by KCl (60 to 80 mmol/L) in sham (n=8), and 140±15 mm Hg by NE and 127±15 mm Hg by KCl in DOCA-salt MA (n=9) (P>0.05).
Increased MAPP caused by NE was stable for >20 minutes in sham and DOCA-salt MA (Figure 2A, 2B). Figure 2C and 2D show tempol (3 mmol/L) responses in sham and DOCA-salt MA. In DOCA-salt MA, tempol caused a larger decrease in MAPP (–87±7% versus –45±6% at 3 mmol/L, P<0.05) and the left-shifted dose-response curve (Figure 2F). Tempol did not change MAPP in KCl-preconstricted sham or DOCA-salt MA (–7±4% and –10±5%, n=5; respectively, P>0.05) (Figure 2E, 2F).
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To determine whether depressor responses caused by tempol could be mimicked by another antioxidant, tiron (3 mmol/L) was applied to NE-preconstricted MA. Tiron did not change MAPP in DOCA-salt (–10±4%, n=4, P>0.05) or sham arteries (–7±3%, n=4, P>0.05).
BK Channel Antagonists Block Depressor Responses Caused by Tempol
We used IBTX (BK channel blocker, 0.1 µmol/L), glibenclamide (ATP-sensitive K+ channel blocker, 1 µmol/L), or apamin (small-conductance Ca2+-activated K+ (SK) channel blocker, 1 µmol/L), and a BK channel selective concentration of TEA (1 mmol/L). IBTX and TEA inhibited tempol-induced depressor responses in sham and DOCA-salt MA (Figure 3A, 3C). IBTX did not affect depressor responses of SNP (1 µmol/L) (Figure 3B, 3C). Apamin and glibenclamide did not affect depressor responses of tempol (Figure 3C).
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Increased BK Channel Function and -Subunit Expression in MA from DOCA-Salt Rats
In anesthetized sham and DOCA-salt rats, the MA constriction caused by IBTX (0.1 µmol/L, 15 minutes) was larger in DOCA-salt than in sham rats (–18±4% versus –8±5%, n=4, P<0.05) (Figure 4A, 4B, 4C). IBTX caused a higher frequency of phasic constrictions in sham than in DOCA-salt MA. Constrictions caused by KCl (80 mmol/L) were similar between DOCA-salt and sham rats (–54±6% versus –50±4%, n=4, P>0.05). The resting MA-OD in sham and DOCA-salt rats was 265±10 µm (n=4) and 275±15 µm (n=4) (P>0.05), respectively.
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In 5 separate comparisons using different protein isolations, immunoblot density corresponding to the BK channel -subunit (100-kDa bands; Figure 5A) were increased by 77±4% in DOCA-salt aorta and 136±7% in DOCA-salt MA compared with levels observed in sham MA (Figure 5B).
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Figure 6A, 6B, and 6C show brightfield images to illustrate isolated VSMC morphology. Immunocytochemical studies in single MA VSMC from 3 sham and DOCA-salt rats showed increased fluorescence intensity in cells from DOCA-salt rats (Figure 6E) compared with those from sham rats (Figure 6D). Immunofluorescence was absent in cells exposed to the anti Kca2+ 1.1 antibody that had been pre-absorbed the competing peptide (Figure 6F).
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Tempol Increased BK Currents in Transfected HEK 293 Cells
Outward currents (Io) were observed in 147 mslo transfected HEK-293 cells from 24 separate transfections. (Figure 7A, 7C). The activation threshold was &0 mV. Io was inhibited by IBTX (0.1 µmol/L, n=4) (Figure 7C). In 12 cells transfected with GFP only, Io was not detected with or without tempol treatment (1 mmol/L) (Figure 7D).
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Tempol (1 mmol/L) reversibly increased peak currents at +80 mV by 30±5% from control levels in mslo transfected HEK-293 cells (P<0.05, n=7, Figure 8A, 8B). Time control studies showed that there were no differences in consecutive current-voltage curves. IBTX (0.1 µmol/L) completely blocked Io activated by tempol (Figure 8A, 8C, n=3).
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When the free Ca2+ level in the pipette solution was reduced (5 nmol/L), the peak Io amplitude recorded at +80 mV decreased from 2.1±0.6 to 1.1±0.3 nA (n=3). The peak Io amplitude recorded under reduced Ca2+ conditions was increased to 1.3±0.3 nA (+16%) (P>0.01, n=3) by tempol (1 mmol/L).
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Discussion |
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Tempol is a SOD mimetic that quenches O2–.2,10 In the present study, tempol caused an NO-independent arterial dilation in sham and DOCA-salt hypertensive rats in situ and in vitro. BK channel antagonists inhibited tempol responses and the data indicate that vascular BK channels contribute to depressor responses caused by tempol. It is also important to note that vasodilation caused by tempol in DOCA-salt rats was larger than in sham rats. This is the first study showing that arterial BK channel activity and expression are increased in DOCA-salt rats and that BK channel upregulation likely contributes to the larger vasodilation caused by tempol in DOCA-salt rats in situ and in vitro. Furthermore, vasodilation caused by tempol was not mimicked by tiron, suggesting that the vasodilation caused by tempol is independent of an SOD mimetic mechanism. This suggestion is supported by the observation that tempol increases Io in mslo transfected HEK-293 cells. These data indicate that tempol may directly activate BK channels.
Function of BK Channels in Arteries
Ca2+ influx through voltage-gated Ca2+ channels regulates vascular tone. Graded increases in intravascular pressure depolarize VSMC activating L-type Ca2+ channels increasing intracellular Ca2+. Increased cytoplasmic Ca2+ activates ryanodine receptors resulting in Ca2+ sparks which activate BK channels. This causes hyperpolarization of the membrane potential (Em), closure of voltage-gated Ca2+ channels, and reducing depolarization.18,19 Blocking BK channels causes Em depolarization, an elevation of intracellular Ca2+ and vasoconstriction.20,21
In the present study, tempol relaxed MA in anesthetized rats in situ, and in isolated, perfused NE pre-constricted but not KCl pre-constricted MA. These initial data suggested that K+ channels contributed to tempol-induced vasodilation. The vasodilation caused by tempol in vitro was blocked by IBTX, a selective BK channel blocker, but not by SK or ATP-sensitive K+ channel blockers. Therefore, the data presented indicate that activation of vascular BK channels is involved in the vasodilation caused by tempol. This effect likely contributes to the depressor responses caused by tempol in vivo. However, K+ channels on VSMC are not the only target for depressor responses caused by tempol. Tempol is known to activate inhibitory mechanisms in the central and peripheral nervous systems that decrease sympathetic nerve activity.7–9 Shokoji et al7 reported that 4-aminopyridine (4-AP) (0.1 mmol/L) blocked reduction of nerve activity by local application of tempol onto renal sympathetic nerves. They concluded that tempol may activate voltage-gated K+ (Kv) channels. Thus, it is possible activation of neuronal K+ channels by tempol may also contribute to depressor responses caused by tempol in vivo.
Upregulation of BK Channels in Arteries from DOCA-Salt Rats
BK channels are composed of pore-forming and accessory ß1 subunits.22,23 Upregulation of BK channel subunit expression and function occurs in VSMC in SHR and aldosterone-salt hypertensive rats,24–28 suggesting that there is a dynamic relationship between BP and BK channels.25,28 Pressure-induced upregulation of BK channel -subunit protein levels and channel function in VSMC provides an important counter-regulatory mechanism to prevent further increases in vascular tone. BK channel activity contributes to resting Em in arteries from hypertensive animals. Arteries from normotensive rats constrict only mildly in response to BK channel inhibition, indicating that K+ efflux through BK channel makes a smaller contribution to resting Em. This scheme is supported by data from studies showing that inhibition of BK channels constricts MA and cerebral arteries in SHRs and aldosterone-salt hypertensive rats.24–29
In the present study, tempol caused larger vasodilations in anesthetized DOCA-salt rats in situ and in isolated and perfused DOCA-salt MA in vitro compared with sham rats. In addition, IBTX caused larger MA constrictions in anesthetized DOCA-salt rats in situ, indicating that BK channel expression or activity was increased. This conclusion is supported by data from Western blot and immunocytochemical analysis showing increased BK channel subunit expression in VSMCs. The ß1 subunit contributes to Ca2+ sensitivity of the channel and therefore to regulation of vascular tone.22,23 However, tempol increased the BK channel Io in mslo only transfected HEK 293 cells. Therefore, the ß1 subunits may not be essential for activation of BK channels caused by tempol.
The Role of O2– in Regulating Vascular BK Channel Function
O2– is elevated in the aorta, and MA from DOCA-salt rats,2,30 scavenging O2– or inhibiting its synthesis will increase the bioavailability of NO and will reduce the activity of the signaling mechanisms activated by O2– to reduce vascular tone. O2– directly inhibits BK channel activity making the channel less sensitive to Ca2+.31 Direct application of peroxynitrite to skeletal muscle resistance and human coronary arteries inhibits BK channel activity and causes vasoconstriction.32,33 Antioxidant treatment restores impaired BK channel function.31,33,34 NO increases BK channel activity in VSMC35 and cslo (canine BK channel -subunit) transfected HEK-293 cells.36 This response is mediated by cGMP-dependent channel phosphorylation. Previous reports indicate that NOS inhibitors do not block tempol effects on BP and RSNA.2,4–6,9 It should be noted that acute treatment with antioxidants (ascorbic acid and tiron), other than tempol, does not lower blood pressure in hypertensive patients37 or in DOCA-salt hypertensive rats,2 although SOD and tiron quench O2– in human saphenous vein and internal mammary artery by >70%.38 Similarly we found that tiron did not mimic the effects of tempol on isolated, perfused NE preconstricted MA, this suggests that reduction of O2– is not the only mechanism by which tempol causes vasodilation. Our results indicated that tempol might directly activate BK channels. This possibility is supported by data obtained from studies of HEK-293 cells transiently transfected with mslo channels. Tempol increased Io in a reversible and IBTX-sensitive manner in these cells. However, it is unclear if tempol is activating mslo by quenching O2– in HEK-293 cells or if the effects of tempol are related to the spin trap properties of tempol. Thus, we cannot completely exclude a role for O2– and NO in tempol caused vasodilation. Therefore, the signaling mediating BK activation channel caused by tempol needs further study. It will also be important to using whole cell and single channel recording techniques to tempol activates BK channels occurs in myocytes.
Tempol converts O2– to hydrogen peroxide (H2O2) which is acted on by endogenous catalase to produce O2 and H2O. Tempol could increase levels of H2O2 over those that can be handled by H2O2-scavenging systems.39 This pathway is relevant to our data as H2O2 relaxes porcine coronary arteries by stimulating BK channel activity via a phospholipase A2-coupled signaling cascade.40 However, in MA, H2O2 induced vasodilation was largely independent of BK channel activity41,42 and exogenous H2O2 inhibits BK channels in skeletal muscle43 and hslo-tranfected HEK-293 cells.44 Endogenous O2– in MA and mslo transfected HEK-293 cells could be converted to H2O2 by tempol and H2O2 could be the activator of BK channels as occurs in coronary arteries. It is also anticipated that this pathway would be unaffected by NOS inhibition accounting for our observation that tempol-induced vasodilation is resistant to L-NAME treatment.
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Conclusion |
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Tempol activates vascular BK channel to cause vasodilation which is larger in DOCA-salt than normotensive rats. Increased BK channel
-subunit protein may provide the fundamental explanation for increased channel activity. Finally, tempol increases Io that in mslo transfected HEK 293 cells and could be blocked by IBTX, providing direct evidence that activation of BK channel contributes to the vasodilation caused by tempol. Tempol causes arterial vasodilation suggesting that the antihypertensive effects of tempol may be mediated by direct activation of BK channel in cardiovascular system,25–30 but the role of O2– in regulation of BK channel function in DOCA-salt hypertension is still unclear.
Perspectives
BK channels are expressed in VSMCs, where they are negative-feedback regulators of vascular tone.18–22 Oxidative stress is prominent in human hypertension and antioxidants have potential therapeutic applications for the treatment of hypertension and associated pathologies. Tempol, a drug that can scavenge O2–, lowers blood pressure after acute treatment of hypertensive rats. Tempol activates vascular BK channel and inhibits sympathetic nerve activity suggesting that the antihypertensive effects of tempol may be mediated by direct dilation of vasculature and inhibition of sympathetic input to the cardiovascular system. Our results indicate that activation of BK channel could reduce blood pressure in hypertensive subjects. These data suggest that drugs, like tempol, that have antioxidant and vascular BK channel activator properties would be novel treatments for the prevention or treatment of hypertension.
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Acknowledgments |
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We thank Dr Christopher J. Lingle, (Department of Anesthesiology, Washington University School of Medicine, St. Louis, Mo) for a gift of the mslo plasmid. We thank Drs James J Galligan and Gregory D Fink for advice. We also thank Catherine M. Rondelli for technical assistance.
This work was supported by National Heart, Lung, and Blood Institute grant numbers: HL-63973, HL-24111, and PO1 HL70687, and by postdoctoral fellowship grant from American Heart Association Mid-West Affiliate for Dr. Xu (0325510Z).
Received July 17, 2005; first decision July 17, 2005; accepted September 1, 2005.
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References |
|---|
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionConclusionReferences |
|---|
- Cai H, Harrison DG. Endothelial dysfunction in cardiovascular diseases-The role of oxidase stress. Cir Res. 2000; 87: 840–844.
[Abstract/Free Full Text] - Xu H, Fink GD, Galligan JJ. Nitric oxide-independent effects of tempol on sympathetic nerve activity and blood pressure in DOCA-salt rats. Am J Physiol Heart Circ Physiol. 2002; 283: H885–H892.
[Abstract/Free Full Text] - Schnackenberg CG, Welch WJ, Wilcox CS. Normalization of blood pressure and renal vascular resistance in SHR with a membrane-permeable superoxide dismutase mimetic: role of nitric oxide. Hypertension. 1998; 32: 59–64.
[Abstract/Free Full Text] - Xu H, Fink GD, Chen A, Watts S, Galligan JJ. Nitric oxide-independent effects of tempol on renal sympathetic nerve activity and blood pressure in normotensive rats. Am J Physiol Heart Circ Physiol. 2001; 281: H975–H980.
[Abstract/Free Full Text] - Shokoji T, Nishiyama A, Fujisawa Y, Hitomi H, Kiyomoto H, Takahashi N, Kimura S, Kohno M, Abe Y. Renal sympathetic nerve responses to tempol in spontaneously hypertensive rats. Hypertension. 2003; 41: 266–273.
[Abstract/Free Full Text] - Xu H, Fink GD, Galligan JJ. Tempol lowers blood pressure and sympathetic nerve activity but not vascular O2– in DOCA-salt rats. Hypertension. 2004; 43: 329–334.
[Abstract/Free Full Text] - Shokoji T, Fujisawa Y, Kimura S, Rahman M, Kiyomoto H, Matsubara K, Moriwaki K, Aki Y, Miyatake A, Kohno M, Abe Y, Nishiyama A. Effects of local administration of tempol and diethyldithio-carbamic on peripheral nerve activity. Hypertension. 2004; 44: 236–243.
[Abstract/Free Full Text] - Lu N, Helwig BG, Fels RJ, Parimi S, Kenney MJ. Central tempol alters basal sympathetic nerve discharge and attenuates sympathetic excitation to central ANG II. Am J Physiol Heart Circ Physiol. 2004; 287: H2626–H2633.
[Abstract/Free Full Text] - Campese VM, Ye S, Zhong H, Yanamadala V, Ye Z, Chiu J. Reactive oxygen species stimulate central and peripheral sympathetic nervous system activity. Am J Physiol Heart Circ Physiol. 2004; 287: H695–H703.
[Abstract/Free Full Text] - Schnackenberg CG, Wilcox CS. Two-week administration of tempol atteneuates both hypertension and renal excretion of 8-iso prostaglandin f2. Hypertension. 1999; 33: 424–428.
[Abstract/Free Full Text] - Beswick RA, Zhang H, Marable D, Catravas JD, Hill WD, Webb RC. Long-term antioxidant administration attenuates mineralocorticoid hypertension and renal inflammatory response. Hypertension. 2001; 37: 781–786.
[Abstract/Free Full Text] - Meng S, Cason GW, Gannon AW, Racusen LC, Manning RD Jr. Oxidative stress in Dahl salt-sensitive hypertension. Hypertension. 2003; 41: 1346–1352.
[Abstract/Free Full Text] - Hoagland KM, Maier KG, Roman RJ. Contributions of 20-HETE to the antihypertensive effects of tempol in Dahl salt-sensitive rats. Hypertension. 2003; 41: 697–702.
[Abstract/Free Full Text] - Zhang Y, Jang R, Mori TA, Croft KD, Schyvens CG, Mckenzie KU. The antioxidant tempol reverses and partially prevents adrenocorticortrophic hormone-induced hypertension in the rat. J Hypertens. 2003; 21: 1513–1518.[CrossRef][Medline] [Order article via Infotrieve]
- Williams JM, Pollock JS, Pollock DM. Arterial pressure response to the antioxidant tempol and ETB receptor blockade in rats on high-salt diet. Hypertension. 2004; 44: 770–775.
[Abstract/Free Full Text] - Watts SW, Fink GD, Northcott CA, Galligan JJ. Endothelin-1-induced venous contraction is maintained in DOCA-salt hypertension; studies with receptor agonists. Br J Pharmacolo. 2002; 137: 69–79.
- Jackson WF, Huebner JM, Rusch NJ. Enzymatic isolation and characterization of single vascular smooth muscle cells from cremasyeric arterioles. Microcirculation. 1997; 1: 35–50.
- Nelson MT, Cheng H, Rubart M, Santana LF, Bonev AD, Knot HJ, Lederer WJ. Relaxation of arterial smooth muscle by calcium sparks. Science. 1995; 270: 633–637.
[Abstract/Free Full Text] - Jaggar JH, Porter VA, Lederer WJ, Nelson MT. Calcium sparks in smooth muscle. Am J Physiol Cell Physiol. 2000; 278: C235–C256.
[Abstract/Free Full Text] - Knot HJ, Nelson MT. Regulation of arterial diameter and wall [Ca2+] in cerebral arteries of rat by membrane potential and intravascular pressure. J Physiol. 1998; 508: 199–209.
[Abstract/Free Full Text] - Knot HJ, Standen NB, Nelson MT. Ryanodine receptors regulate arterial dimater and wall [Ca2+] cerebral arteries of rat via Ca2+-dependent K+ channels. J Physiol. 1998; 508: 211–221.
[Abstract/Free Full Text] - Knaus HG, Garcia-Calvo M, Kaczorowski GJ, Garcia ML. Subunit composition of the high conductance calsium-activated potassium channel from smooth muscle, a representative of the mslo and slowpoke family of potassium channels. J Bio Chem. 1994; 269: 3921–3924.
[Abstract/Free Full Text] - Tanaka Y, Meera P, Song M, Knaus HG, Toro L. Molecular constitutents of maxi Kca channels in human coronary smooth muscle: predominant + ß subunit complexes. J Physiol. 1997; 502: 545–575.[CrossRef][Medline]
[Order article via Infotrieve]
- Liu Y, Jones AW, Sturek M. Ca2+-dependent K+ current in arterial smooth muscle cells from aldosterone-salt hypertensive rats. Am J Physiol. 1995; 269: H1246–H1257.[Medline] [Order article via Infotrieve]
- Liu Y, Pleyte K, Knaus HG, Rusch NY. Increased expression of Ca2+-sensitive K+ channels in aorta of hypertensive rats. Hypertension. 1997; 30: 1403–1409.
[Abstract/Free Full Text] - Liu Y, Huudetz AG, Knaus HG, Rusch N. Increased expression of Ca2+-sensitive K+ channels in the cerebral microcirculation of genetically hypertensive rats-evidence for their protection against cerebral vasospasm. Circ Res. 1998; 82: 729–737.
[Abstract/Free Full Text] - Cox RH, Rusch NY. New expression profiles of voltage-gated ion channels in arteries exposed to high blood pressure. Microcirculation. 2002; 9: 243–257.[CrossRef][Medline] [Order article via Infotrieve]
- Rusch NJ, Runnel AM. Remission of high blood pressure reverses arterial potassium channel alteration. Hypertension. 1994; 23: 941–945.
[Abstract/Free Full Text] - Cox RH, Lozinskaya I, Dietz NJ. Calcium exerts a larger regulatory effect on potassium channels in small mesenteric artery mycoytes from spontaneously hypertensive rats compared to Wistar-Kyoto rats. Am J Hypertens. 2003; 16: 21–27.[CrossRef][Medline] [Order article via Infotrieve]
- Somers MJ, Mavromatis K, Galis ZS, Harrison DG. Vascular superoxide production and vasomotor function in hypertension induced by deoxycorticorsterone acetate-salt. Circulation. 2000; 101: 1722–1728.
[Abstract/Free Full Text] - Erdös B, Simandle SA, Snipes JA, Miller AW, Busija DW. Potassium channel dysfunction in cerebral arteries of insulin-resistant rats is mediated by reactive oxygen species. Stroke. 2004; 35: 964–969.
[Abstract/Free Full Text] - Liu Y, Terata K, Chai Q, Li H, Kleinman LH, Gutterman DD. Peroxynitrite inhibits Ca2+-activated K+ channel activity in smooth muscle of human coronary arterioles. Circ Res. 2002; 91: 1070–1081.
[Abstract/Free Full Text] - Frisbee JC, Maier KG, Stepp DW. Oxidant stress-induced increase in myogenic activation of skeletal muscle resistance arteries in obese Zucker rats. Am J Physiol Heart Circ Physiol. 2002; 283: H2160–H2168.
[Abstract/Free Full Text] - Ross J, Armstead WM. Differential role of PTK and ERK MAPK in superoxide impairment of KATP and KCa channel cerebrovasodilation. Am J Physiol Regul Integr Comp Physiol. 2003; 285: R149–R154.
[Abstract/Free Full Text] - Bolotina VM, Najibi S, Palacino JJ, Pagano PJ, Cohen RA. Nitric oxide directly activates calcium-dependent potassium channels in vascular smooth muscle. Nature. 1994; 368: 850–853.[CrossRef][Medline] [Order article via Infotrieve]
- Fukao M, Mason HS, Britton FC, Kenyon JL, Horowitz B, Keef KD Cyclic GMP-dependent Protein Kinase activates cloned BKCa channels expressed in mammalian cells by direct phosphorylation at serine 1072. J Biol Chem. 1999; 274: 10927–10935.
[Abstract/Free Full Text] - Duffy SJ, Gokce N, Holbrook M, Hunter LM, Biogelsen ES, Huang A, Keaney JF, Vita JF. Effect of ascorbic acid treatment on conduit vessel endothelia dysfunction in patients with hypertension. Am J Physiol Heart Circ Physiol. 2001; 280: H528–H534.
[Abstract/Free Full Text] - Guzik TJ, West NEJ, Pillai R, Taggart DP, Channon KM. Nitric oxide modulates superoxide release and peroxynitrite formation in human blood vessels. Hypertension. 2002; 39: 1088–1094.
[Abstract/Free Full Text] - Chen YF, Cowley Aw Jr., Zhou AP. Increased H2O2 counteracts the vasodilator and natriuretic effects of superoxide dismutation by tempol in renal medulla. Am J Physiol Regul Integr Comp Physiol,. 2003; 285: R827–R833.
[Abstract/Free Full Text] - Barlow RS, El-Mowafy AM, White RE. H2O2 opens BK channels via the PLA2-arachidonic acid signaling cascade in coronary artery smooth muscle. Am J Physiol Heart Circ Physiol,. 2000; 279: H475–H483.
[Abstract/Free Full Text] - Lucchesi PA, Belmadani S, Matrougui K. Hydrogen peroxide acts as both vasodilator and vasoconstrictor the control of perfused mouse mesenteric resistance arteries. J Hypertens. 2005; 23: 571–579.[Medline] [Order article via Infotrieve]
- Gao YJ, Hirota S, Zhang DW, Janssen LJ, Lee RM. Mechanisms of hydrogen-oeroxide-induced biphysic response in rat mesenteric artery. Br J Pharmacol. 2003; 138: 1085–1092.[CrossRef][Medline] [Order article via Infotrieve]
- Soto MA, Gonzalez C, Lissi E, Vergara C, Latorr R. Ca(2+)-activated K+ channel inhibition by reactive oxgen species. Am J Physiol Cell Physiol. 2002; 282: C461–C467.
[Abstract/Free Full Text] - DiChiara TJ, Reinhart PH. Redox modulation of hslo Ca2+ activated K+ channels. J Neurosci. 1997; 17: 4942–4955.
[Abstract/Free Full Text]
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