This Article Abstract Full Text (PDF) All Versions of this Article: 44/6/897    most recent 01.HYP.0000146536.68208.84v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Shimosawa, T. Articles by Fujita, T. Search for Related Content PubMed PubMed Citation Articles by Shimosawa, T. Articles by Fujita, T. Related Collections Hypertension - basic studies Ion channels/membrane transport Autonomic, reflex, and neurohumoral control of circulation

(Hypertension. 2004;44:897.)
© 2004 American Heart Association, Inc.

Scientific Contributions

Magnesium Inhibits Norepinephrine Release by Blocking N-Type Calcium Channels at Peripheral Sympathetic Nerve Endings

From the Department of Internal Medicine, Faculty of Medicine, University of Tokyo, Bunkyo-ku, Tokyo, Japan.

Correspondence to Toshiro Fujita, MD, Department of Internal Medicine, Faculty of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8655, Japan. E-mail fujita-dis{at}h.u-tokyo.ac.jp

	Abstract

Top Abstract Introduction Methods Results Discussion References

 
Although Mg²⁺ contributes to blood pressure regulation partly in terms of vasodilator action, its sympatholytic effect may also play an important role to control blood pressure. Thus, in the present study, we investigated the effect of Mg²⁺ on sympathetic tone and blood pressure. We studied its actions on the blood pressure response to hydralazine, a direct vasodilator, in conscious spontaneously hypertensive rats (SHRs), and to electrical stimulation in the pithed Sprague–Dawley rat; catecholamine release by peripheral sympathetic nerve endings; and the N-type Ca²⁺ channels of cultured neural cells. Intravenous Mg²⁺ infusion (MgSO₄: 3x10^–6 mol/kg body weight/min) induced the greater hypotensive response to hydralazine with attenuated reflex tachycardia in SHRs. In pithed rats, Mg²⁺ infusion significantly attenuated the blood pressure elevation (2±2 mm Hg versus 27±6 mm Hg, P<0.01) in response to spinal electrical stimulation. In the perfused mesenteric arteries system, norepinephrine release was significantly attenuated (51±2%, P<0.01) by high Mg²⁺ concentration solution (4.8 mmol/L) compared with normal Mg²⁺ solution (1.2 mmol/L). When we applied the perforated whole-cell patch clamp method to nerve growth factor-treated PC12 cells, Mg²⁺ blocked voltage-gated Ca²⁺ currents in a concentration-dependent manner. The majority of the voltage-gated Ca²⁺ currents were carried through N-type channels, followed by L-type channels. Mg²⁺ blocked both of these channels. These findings suggest that Mg²⁺ blocks mainly N-type Ca²⁺ channels at nerve endings, and thus inhibits norepinephrine release, which decreases blood pressure independent of its direct vasodilating action.

Key Words: hypertension • catecholamines • ion channels • cocaine

	Introduction

Top Abstract Introduction Methods Results Discussion References

 
The second most plentiful cation in intracellular fluid and an essential element for the activity of many enzymes is Mg²⁺.¹ In addition to these biochemical actions, magnesium salts have been shown to lower blood pressure.^2,3 The hypotensive effect of Mg²⁺ has been found to be mediated by nonspecific antagonism of the Ca²⁺ channels in vascular smooth muscle cells.^4,5 On the contrary, Mg²⁺ deficiency results in a high catecholamine level, altered barofunction, and hypertension.^6,7 Sympathoactivation and catecholamine elevation induce tachycardia, glucose intolerance, and abnormal fat metabolism, as well as direct cardiotoxicity.^8,9 At the same time, recent clinical studies revealed that Mg²⁺ protects brain from ischemic damages.^10,11 The mechanism for neuroprotection of Mg²⁺ is not fully elucidated; however, similar to Mg²⁺ effect on vasculature, it is speculated that Mg²⁺-induced decrease in intracellular Ca²⁺ plays an important role. It can be hypothesized that Mg²⁺ effect on Ca²⁺ homeostasis in neural cells may be a common mechanism between sympathoinhibitory and neuroprotective action of Mg²⁺.

In the present study, we performed in vivo and ex vivo experiments to investigate the effect of Mg²⁺ on circulatory control by modulating sympathetic tone. Also, we investigated the in vitro effect of extracellular Mg²⁺ concentrations on the voltage-gated Ca²⁺ current of nerve growth factor (NGF)-differentiated PC12 cells, which have characteristics in common to peripheral sympathetic nerves.^12,13

	Methods

Top Abstract Introduction Methods Results Discussion References

 
For a detailed Methods section, please see http://hyper.hypertensionaha.org.

All protocols in this study were approved by the ethics committee of our institution, and rats were handled in our accredited facility in accordance with the institutional animal care policies of the University of Tokyo. All research protocols conformed to the guiding principles for animal experimentation as enunciated by the Ethics Committee on Animal Research of the University of Tokyo, Faculty of Medicine.

Protocol 1: Sympatholytic Effect of Mg²⁺ and Blood Pressure Changes In Vivo
Male spontaneously hypertensive rats were used in this experiment. The rats were divided into 2 groups: Mg²⁺ group (n=8) and a control group (n=7). In the Mg²⁺ group, MgSO₄ (3x10^–6 mol/kg body weight/min) was infused, and in the control group saline was infused. Responses to hydralazine (1, 3, and 6x10^–5 g/kg body weight) were observed. A 100 µL blood sample was drawn before and after saline or MgSO₄ infusion to measure the serum Mg level. The nadir mean arterial pressure (MAP) and peak heart rate (HR) in 2 groups were compared.

Male Sprague–Dawley rats were pithed as described elsewhere.¹⁴ Briefly, rats were pithed by inserting a steel rod covered with enamel except at its tip (5 mm), and its end was positioned at the level of the 7th to 10th thoracic vertebrae. The rats were divided into 2 groups as described. After infusion for 20 minutes, we stimulated at 0.5 Hz for 1 minute with an electrical stimulator between the pithing rod and the indifferent electrode. Each stimulus was 50 V and 1 millisecond. Blood pressure and HR changes were observed. To confirm quality of pithing, the rats were injected with 1 mg/kg hexamethonium, and responses to electrical stimulation were observed after the aforementioned experiments.

Protocol 2: Effect of Mg²⁺ on Norepinephrine Release by Peripheral Sympathetic Nerve Ending
The superior mesenteric artery from Sprague–Dawley rats was prepared by a modification of Castellucci method.¹⁵ The preparations were perfused with a Krebs–Henselit solution with 1.2 mmol/L of Mg²⁺. Low-Mg²⁺ buffer was prepared by reducing the MgSO₄ concentration to 0.3 mmol/L substitution with Na₂SO₄, and high-Mg²⁺ buffer with a magnesium concentration of 3.6 mmol/L was prepared by replacing NaCl with MgCl₂ iso-osmotically.

A platinum electrode was placed around the periarterial plexus of the mesenteric artery, and every 15 minutes we stimulated at 8 Hz for 1 minute. Each stimulus was 10 V and 1 millisecond. The perfusate through the mesenteric vascular preparation was collected for measurement of norepinephrine (NE) by high-performance liquid chromatography.¹⁵ NE overflow was defined as NE content of perfusates per wet mesenteric artery weight. To identify component of NE overflow that was affected by Mg²⁺, we applied cocaine, a specific blocker of NE reuptake by nerve tissue,¹⁶ or deoxycorticosterone, a blocker of NE uptake by non-neuronal tissue.¹⁷

Protocol 3: Effect of Extracellular Mg²⁺ on Voltage-Gated Ca²⁺ Channels
The PC12 cells were cultured in Dulbecco modified eagle medium containing 10% fetal calf serum and 2.5 S NGF (10 ng/mL) for 7 days. We selected cells with neurite outgrowth for the electrophysiology experiments.

The perforated whole-cell clamp technique¹⁸ was used to avoid the run-down of voltage-gated Ca²⁺ currents. Ba²⁺ ion was used as a charge carrier through the voltage-gated Ca²⁺ channels. The standard patch electrode solution contained 1.2 mmol/L of Mg²⁺. Low-Mg²⁺ and the high-Mg²⁺ extracellular solutions were prepared as described in protocol 2. Extracellular solutions containing different concentrations of Mg²⁺ were applied by changing the perfusion solution. All the data were corrected for the liquid junction potential (–4 to –2 mV). Amphotericin B (200 µg/mL) was used for the perforated whole-cell clamp experiments.

An L-type Ca²⁺ channel blocker, nitrendipine (NIT) (5 µmol/L), and an N-type Ca²⁺ channel blocker, -conotoxin GVIA (-CgTX) (1 µmol/L), were used to identify the type of voltage-gated Ca²⁺ current.

Statistical Analysis
In protocol 2, the average of the control responses of NE overflow to electrical stimulation and the following 2 responses in the different Mg²⁺ concentration buffers or in the presence of drugs were calculated. The results are expressed as total NE overflow standardized by tissue weight and the percent change from the averaged NE overflow in control buffer.

Data are shown as means±SEM in protocols 1 and 2 and as means±SD in protocol 3. The statistical analysis in protocol 2 was performed by the paired and unpaired Student t test, and in protocols 1 and 3 by analysis of variance (ANOVA). P<0.05 was considered indicative of statistical significance.

	Results

Top Abstract Introduction Methods Results Discussion References

 
Protocol 1: Sympatholytic Effect of Mg²⁺ and Blood Pressure Changes In Vivo
The body weight of the rats infused with Mg²⁺ (Mg²⁺ group) was 241±2g, their baseline MAP was 175±5 mm Hg, and their HR was 453±9 bpm, which were not affected by the Mg²⁺ infusion (MAP, 170±4 mm Hg; HR, 440±7 bpm). The serum Mg level significantly increased from 2.5±0.05 mg/dL to 3.5±0.11 mg/dL after Mg²⁺ infusion (P<0.01). The body weight of the rats in the control group was 245±4g, their baseline MAP was 173±3 mm Hg, and their HR was 442±12 bpm. None of those parameters changed much after saline infusion in the control group (MAP, 174±5 mm Hg; HR, 444±10 bpm; serum magnesium from 2.5±0.05 mg/dL to 2.5±0.06 mg/dL). Hydralazine decreased MAP dose-dependently and the decrease was more prominent in the Mg²⁺ group than control group (Figure 1a), whereas HR increased more in the control group than in the Mg²⁺ group (Figure 1b).

View larger version (14K): [in this window] [in a new window]   Figure 1. BP and heart rate (HR) responses to hydralazine in control and Mg2+ infused groups. a, Decreases in MAP of the Mg2+ group (•) were significantly larger than those of the control group (). b, Increases in HR of the Mg2+ group (•) were significantly smaller than those of the control group (). Data are presented as means±SEM. P<0.01 by ANOVA and Sheffe method.

Blood Pressure Response to Electrical Stimulation in Pithed Sprague–Dawley Rats
The body weight of the rats infused with Mg²⁺ (Mg²⁺ group) was 271±10g, their baseline MAP after pithing was 55±11 mm Hg, and their HR was 206±25 bpm. The body weight of the rats in the control group was 275±16g, their baseline MAP after pithing was 53±10 mm Hg, and their HR was 208±22 bpm. Electrical stimulation significantly increased both MAP and HR, but the extent of the increase was greater in the control group than in the Mg²⁺ group (Figure 2). The pressor responses to electrical stimulation were completely abolished (n=3; MAP, 55±8 to 53±4 mm Hg; HR, 205±10 to 204±8 bpm) by 1 mg/kg hexamethonium, suggesting that the pressor response reflects peripheral sympathetic stimulation.

View larger version (37K): [in this window] [in a new window]   Figure 2. Blood pressure responses to electrical stimulation in pithed rat. a, Representative traces of blood pressure changes by electrical stimulation from control (right panel) and Mg2+ group (left panel). Increases in MAP (b) and HR (c) were significantly attenuated in the Mg2+ group compared with the control group (P<0.01 and P<0.05 by ANOVA and Dunnet method). Data are presented as means ± SEM.

Protocol 2: Effect of Mg²⁺ on NE Release From Peripheral Sympathetic Nerve Endings
NE overflow at 1.2 mmol/L Mg²⁺ was 0.266±0.032 ng/g tissue weight, and percent change of NE overflow with each buffer is shown in the Table. High-Mg²⁺ buffer significantly suppressed NE overflow.

In the presence of cocaine or deoxycorticosterone, the high-Mg²⁺ buffer significantly attenuated NE overflow, and the Mg²⁺-induced changes were not significantly altered.

Protocol 3: Effect of Extracellular Mg²⁺ on the Voltage-Gated Ca²⁺ Currents
To determine the effect of extracellular Mg²⁺ on NE release, we investigated the effect of extracellular Mg²⁺ on the voltage-gated Ca²⁺ currents of PC12 cells differentiated by NGF. Figure 3A shows the Ba²⁺ currents through voltage-gated Ca²⁺ channels recorded under the voltage clamp from a PC12 cell at 3 different extracellular Mg²⁺ concentrations. The holding potential was –74 mV, and a test pulse step to 6 mV was applied. The Ba²⁺ current exhibited a clear inactivation process, but the steady current persisted. The Ba²⁺ current first appeared at a potential step to –34 mV. As the depolarizing steps became greater, the amplitude of the Ba²⁺ current increased. When the extracellular Mg²⁺ concentration was changed sequentially, the amplitude of the peak current was largest in the 0.3 mmol/L Mg²⁺ solution, smaller in the standard extracellular solution (1.2 mmol/L Mg), and smallest in the 4.8 mmol/L Mg²⁺ solution. Increases in the extracellular Mg²⁺ concentration inhibited the voltage-gated Ca²⁺ current, and the inhibition was reversible when the extracellular solution was changed to the 0.3 mmol/L Mg²⁺ solution (0.3 mmol/L Mg²⁺ recover).

View larger version (23K): [in this window] [in a new window]   Figure 3. Effect of extracellular Mg2+ on voltage-gated Ca2+ current. Currents were recorded under voltage-clamp with the perforated whole-cell clamp technique from a PC12 cell differentiated by NGF. A, Ba2+ currents were evoked by a pulse step to 6 mV from the holding potential of –74 in extracellular solutions containing 0.3 mmol/L Mg2+, 1.2 mmol/L Mg2+, 4.8 mmol/L Mg2+, and again in 0.3 mmol/L Mg2+ to examine the recovery. B, The current–potential relationship of the Ba2+ current in each Mg2+ level (•, 0.3 mmol/L; , 1.2 mmol/L; , 4.8 mmol/L) are plotted. The ordinate indicates the peak amplitude of the Ba2+ current in pA and the abscissa indicates test potential in mV. C, Concentration dependency of the effect of Mg2+ on the Ba2+ current. The amplitude of the peak Ba2+ current in the 1.2 mmol/L Mg2+ solution was normalized as 100% in each record. The mean amplitude of the current in 1.2 mmol/L Mg2+ solution was 124±44 pA. Means and standard deviations of the currents in 0.3 mmol/L, 3.6 mmol/L, 2.4 mmol/L, and 4.8 mmol/L Mg2+ normalized to that in 1.2 mmol/L Mg2+ were 124±19%, 83±10%, 75±7%, and 68±15%, respectively. *Statistical significance (P<0.05) using 1-way ANOVA with Tukey multiple comparison test.

The current–potential relationships of the Ba²⁺ current in the extracellular solutions containing 3 different Mg²⁺ concentrations are shown in Figure 3B. Increased extracellular Mg²⁺ induced a decrease in amplitude of the Ba²⁺ current at all potentials, indicating that inhibition of the Ba²⁺ current was not voltage-dependent. Figure 3C summarizes the amplitude of the Ba²⁺ current at the 3 Mg²⁺ concentrations. The amplitude of the peak Ba²⁺ current in the standard extracellular solution was normalized as 100% in each record. Extracellular Mg²⁺ inhibited the Ba²⁺ current in a concentration-dependent manner when analyzed by repeated measures ANOVA with post-test for linear trend. We could observe significant linear trend (P<0.0001).

Figure 4A shows the sequential effect of NIT (5 µmol/L) and 4.8 mmol/L Mg²⁺ on the Ba²⁺ current. Application of NIT decreased the current by 17% of the control, and additional application of high-Mg²⁺ solution inhibited the current by an additional 21% of the control. Figure 4B shows the sequential effect of -CgTX (1 µmol/L) and 4.8 mmol/L Mg²⁺ on the Ba²⁺ current, and application of -CgTX decreased the current by 78% of the control. Additional application of 4.8 mmol/L Mg²⁺ solution inhibited the current by only an additional 5% of the control.

View larger version (26K): [in this window] [in a new window]   Figure 4. Inhibition of N-type Ca2+ current by high Mg2+. A, Effect of L-type Ca2+ channel blocker, nitrendipine (NIT), and high Mg2+ on the Ba2+ current. The Ba2+ current was evoked by the pulse step to 6 mV from the holding potential of –74 mV. The amplitude of the peak current was measured every 10 seconds. The ordinate indicates percentage of the Ba2+ current as compared with the control (before application of NIT in 1.2 mmol/L Mg2+) and the abscissa the time course of the application of 5 µmol/L NIT and 4.8 mmol/L Mg2+. After NIT attained its maximal effect, 4.8 mmol/L Mg2+ solution with NIT was applied. B, Effect of N-type Ca2+ channel blocker, -conotoxin GVIA (CgTX), and 4.8 mmol/L Mg2+ on the Ba2+ current. The Ba2+ current was recorded by the same method as in (A). The ordinate indicates percentage of the Ba2+ current as compared with the control (before application of CgTX in 1.2 mmol/L Mg2+) and the abscissa, and the time course of the application of 1 µmol/L CgTX and 4.8 mmol/L Mg2+. After CgTX attained its maximal effect, 4.8 mmol/L Mg2+ solution with CgTX was applied. C, Summary of the experiments. The ordinate indicates the mean and standard deviation of the normalized Ba2+ current as compared with the control (before application of channel blocker in 1.2 mmol/L Mg2+). High Mg2+ indicates application of 4.8 mmol/L Mg2+ solution.

Figure 4C summarizes the data obtained in these experiments. Application of NIT inhibited the Ba²⁺ current to 83.5±5.6% (n=15) of the control, and additional application of 4.8 mmol/L Mg²⁺ inhibited it to 59.4±7.5% (n=15) of the control. There was a significant difference (P<0.001 by paired t test) between the current after NIT and after NIT plus 4.8 mmol/L Mg²⁺. Application of -CgTX inhibited the Ba²⁺ current to 13.1±2.6% (n=15) of the control, and additional application of 4.8 mmol/L Mg²⁺ inhibited it to 7.7±1.3% (n=15) of the control. There was a significant difference (P<0.001 by paired t test) between the current after -CgTX and after -CgTX plus 4.8 mmol/L Mg²⁺. The current–potential relationships of the non–L-type currents and non–N-type currents before and after high Mg²⁺ (4.8 mmol/L) application are shown in Figure 5A and B, respectively. Both non–L-type and non–N-type currents were inhibited by high Mg²⁺. These results indicated that the Ba²⁺ current in NGF-treated PC12 cells was mainly carried through N-type Ca²⁺ channels and the majority of the remaining current was L-type Ca²⁺ channels, and that both of these currents are inhibited by high Mg²⁺.

View larger version (15K): [in this window] [in a new window]   Figure 5. Effect of 4.8 mmol/L Mg2+ on the current–potential relationship of non–L-type (mostly N-type) and non–N-type (mostly N-type) currents. A, The current–potential relationship of the Ba2+ current in extracellular solutions containing 5 µmol/L nitrendipine in 2 Mg2+ levels (•, 1.2 mmol/L; , 4.8 mmol/L) are plotted. B, The current–potential relationship of the Ba2+ current in extracellular solutions containing 1 µmol/L -conotoxin GVIA in 2 Mg2+ levels (•, 1.2 mmol/L; , 4.8 mmol/L) are plotted. The ordinate indicates the peak amplitude of the Ba2+ current in pA and the abscissa indicates test potential in mV.

	Discussion

Top Abstract Introduction Methods Results Discussion References

 
Mg²⁺ is reported to modulate cardiac function and vasomotor control by nonspecific antagonism of the Ca²⁺ channels.^{4,5,7,19–21} Mg²⁺ also modulates neuronal activity^6,7 but the precise mechanisms are still unknown. In the present study, we showed an Mg²⁺ effect on sympathetic tone both in in vivo and in vitro studies. Firstly, using both conscious spontaneously hypertensive rats and pithed rats, we showed that Mg²⁺ possesses sympatholytic effects and reduces blood pressure. Secondary, using perfused mesenteric artery preparation, we revealed that Mg²⁺ reduces norepinephrine release. Finally, Mg²⁺ inhibits N-type Ca²⁺ channels in differentiated PC12 cells. The results of the present study indicate that Mg²⁺ attenuated sympathetic tone mainly by inhibiting N-type Ca²⁺ channels.

Mg²⁺ augmented the antihypertensive effect of hydralazine and attenuated the reflex tachycardia. It suggests that Mg²⁺ exerts an inhibitory effect on sympathetic tone and enhances the vasodilator effect of hydralazine. To further investigate roles of peripheral sympathetic nerves on blood pressure regulation, we applied the mechanically pithed preparation in which central nervous activities are fully destroyed and also we can avoid pharmacological interference. Electrical stimuli were applied at the level of 7th to 10th thoracic vertebrae to direct stimulation of cardiac sympathetic nerve be possible.¹⁴ Mg²⁺ attenuated blood pressure elevation evoked by sympathetic nerve stimulation. Norepinephrine is a main factor that is released by electrical stimulation and regulates blood pressure in the pithed model; however, other circulatory factors could be released. Thus, we applied ex vivo model to investigate effect of Mg²⁺ on norepinephrine release. We measured NE overflow from the periarterial plexus of the mesenteric artery. There are 2 components to NE overflow: NE release from nerve endings and NE reuptake into nerve terminals and other tissue. We showed that Mg²⁺ affects NE release but not uptake by using uptake blockers such as cocaine¹⁶ and deoxycorticosterone.¹⁷

To specify Mg²⁺ effect on Ca²⁺ channels that play a pivotal role in sympathetic activity, we used NGF-treated PC12 cells. NGF-treated PC12 cells exhibited neurite outgrowth. Approximately 90% of the voltage-gated Ca²⁺ channel currents were composed of -CgTX-sensitive N-type Ca²⁺ currents. An L-type Ca²⁺ channel blocker, NIT, reduced Ca²⁺ influx to a smaller extent than -CgTX. These characteristics are consistent with those of differentiated PC12 cells, which have characteristics similar to those of noradrenergic sympathetic neurons, including the development of N-type Ca²⁺ channels.^12,13,22 In the present study, Mg²⁺ further inhibited the Ba²⁺ current after treatment with NIT but not after -CgTX, suggesting that Mg²⁺ inhibits N-type Ca²⁺ channels. The high Mg²⁺-induced inhibition of N-type Ca²⁺ channels observed in the present study was similar to the effect of pro-adrenomedullin N-terminal 20 peptide on the N-type current in NGF-treated PC 12 cells.¹⁸ This inhibition of the N-type Ca²⁺ current plays a role in the inhibition of Ca²⁺ influx through voltage-gated Ca²⁺ channels and as a result reduces the intracellular Ca²⁺ concentration.

Based on these results, extracellular Mg²⁺ blocks N-type and partly L-type Ca²⁺ channels, and thus inhibits NE release, and these effects play an important role in regulating sympathetic tone and blood pressure.

Perspectives
Recent large clinical studies have shown that the lower the blood pressure obtained by treatment, the more successful in preventing hypertensive patients from cardiovascular events.^23–25 Although dihydropyridine Ca²⁺ channel blockers are potent antihypertensive agents, short-acting Ca²⁺ channel blockers have been shown to be unfavorable for the treatment of hypertension.²⁶ This may be partly caused by reflex sympathoactivation and catecholamine release, which induce unfavorable effects.^8,9 Several epidemiological studies have supported tachycardia, an indicator of sympathetic tone, as an independent risk factor for cardiovascular death in elderly men.²⁷ Because all vasodilators induce reflex sympathoactivation in hypertensive patients, treatment that aims to reduce sympathoactivation can achieve a greater therapeutic effect. Because Mg²⁺ decreases NE release from nerve endings by inhibiting voltage-gated N-type Ca²⁺ currents, Mg²⁺ may be beneficial in preventing organ damage by inhibiting reflex sympathoactivation. In fact, some studies have shown that Mg²⁺ supplementation improves the outcome of cardiovascular diseases.^11,28 However, the antihypertensive action of Mg²⁺ is very weak.²⁹ It led us to the speculation that Ca²⁺ channel blockers with the inhibitory action of both an L-type and N-type Ca²⁺ channels such as cilnidipine^30–32 might be efficacious for the treatment of hypertension.

Received March 8, 2004; first decision March 30, 2004; accepted September 21, 2004.

	References

Top Abstract Introduction Methods Results Discussion References

 
1. Rude RK. Physiology of magnesium metabolism and the important role of magnesium in potassium deficiency. Am J Cardiol. 1989; 63: 31G–34G.[CrossRef][Medline] [Order article via Infotrieve]

2. Touyz RM, Milne FJ. Magnesium supplementation attenuates, but does not prevent, development of hypertension in spontaneously hypertensive rats. Am J Hypertens. 1999; 12: 757–765.[CrossRef][Medline] [Order article via Infotrieve]

3. Kawano Y, Matsuoka H, Takishita S, Omae T. Effects of Magnesium supplementation in hypertensive patients. Hypertension. 1998; 32: 260–265.[Abstract/Free Full Text]

4. Delpiano MA, Altura BM. Modulatory effect of extracellular Mg²⁺ ions on K⁺ and Ca²⁺ currents of capillary endothelial cells from rat brain. FEBS Lett. 1996; 394: 335–339.[CrossRef][Medline] [Order article via Infotrieve]

5. Zhang A, Fan SH, Cheng TP, Altura BT, Wong RK, Altura BM. Extracellular Mg²⁺ modulates intracellular Ca²⁺ in acutely isolated hippocampal CA1 pyramidal cells of the guinea-pig. Brain Res. 1996; 728: 204–208.[Medline] [Order article via Infotrieve]

6. Murasato Y, Harada Y, Ikeda M, Nakashima Y, Hayashida Y. Effect of magnesium deficiency on autonomic circulatory regulation in conscious rats. Hypertension. 1999; 34: 247–252.[Abstract/Free Full Text]

7. Altura BM, Altura BT, Gebrewold A, Ising H, Gunther T. Magnesium deficiency and hypertension: correlation between magnesium-deficient diets and microcirculatory changes in situ. Science. 1984; 223: 1315–1317.[Abstract/Free Full Text]

8. Frohlich ED, McLoughlin MJ, Losem CJ, Ketelhut R, Messerli FH. Hemodynamic comparison of two nifedipine formulations in patients with essential hypertension. Am J Cardiol. 1991; 68: 1346–1350.[CrossRef][Medline] [Order article via Infotrieve]

9. Zdanowicz MM, Barletta MA. Protective role of magnesium in catecholamine-induced arrhythmia and toxicity in vitro. Magnesium Research. 1991; 4: 153–162.[Medline] [Order article via Infotrieve]

10. Crowther CA, Hiller JE, Doyle LW, Haslam RR. Effect of magnesium sulfate given for neuroprotection before preterm birth: a randomized controlled trial. JAMA. 2003; 290: 2669–2676.[Abstract/Free Full Text]

11. Muir KW, Lees KR, Ford I, Davis S. Magnesium for acute stroke (Intravenous Magnesium Efficacy in Stroke trial): randomised controlled trial. Lancet. 2004; 363: 439–445.[CrossRef][Medline] [Order article via Infotrieve]

12. Lewis DL, De Aizpurua HJ, Rausch DM. Enhanced expression of Ca²⁺ channels by nerve growth factor and the v-src oncogene in rat pheochromocytoma cells. J Physiol (Lond). 1993; 465: 325–342.[Abstract/Free Full Text]

13. Greene L, Tischler A. PC12 pheochromocytoma cultures in neurobiological research. Adv Cell Neurobiol. 1982; 3: 373–414.

14. Shimosawa T, Fujita T. Hypotensive effect of newly identified peptide, proadrenomedullin N-terminal 20 peptide. Hypertension. 1996; 28: 325–329.[Abstract/Free Full Text]

15. Shimosawa T, Ito Y, Ando K, Kitamura K, Kangawa K, Fujita T. Proadrenomedullin NH₂-terminal 20 peptide, a new product of the adrenomedullin gene, inhibits norepinephrine overflow from nerve endings. J Clin Invest. 1995; 96: 1672–1676.[Medline] [Order article via Infotrieve]

16. Pitts DK, Marwah J. Autonomic actions of cocaine. Can J Physiol Pharmacol. 1988; 67: 1168–1176.

17. Salt P. Inhibition of noradrenaline uptake in the isolated rat heart by steroids, clonidine and methoxylated phenylethylamines. Eur J Pharmacol. 1979; 20: 329–340.

18. Takano K, Yamashita N, Fujita T. Proadrenomedullin N-terminal 20 peptide inhibits the voltage-gated Ca²⁺ channel current through a pertussis toxin-sensitive G protein in rat pheochromocytoma-derived PC 12 cells. J Clin Invest. 1996; 98: 14–17.[Medline] [Order article via Infotrieve]

19. Altura BM, Altura BT. Influence of magnesium on drug-induced contractions and ion content in rabbit aorta. Am J Physiol. 1971; 220: 938–944.[Free Full Text]

20. Turlapaty PDMV, Altura BM. Extracellular magnesium ions control calcium exchange and content of vascular smooth muscle. Eur J Pharmacol. 1978; 52: 421–423.[CrossRef][Medline] [Order article via Infotrieve]

21. Fujita T, Ito Y, Ando K, Noda H, Ogata E. Attenuated vasodilator responses to Mg 2+ in young patients with borderline hypertension. Circulation. 1990; 82: 384–393.[Abstract/Free Full Text]

22. Takahashi M, Tsukui H, Hanada H. Neuronal differentiation of Ca²⁺ channel by nerve growth factor. Brain Res. 1985; 341: 381–384.[CrossRef][Medline] [Order article via Infotrieve]

23. Brown MJ, Palmer CR, Castaigne A, de Leeuw PW, Mancia G, Rosenthal T, Ruilope LM. Morbidity and mortality in patients randomised to double-blind treatment with a long-acting calcium-channel blocker or diuretic in the International Nifedipine GITS study: Intervention as a Goal in Hypertension Treatment (INSIGHT). Lancet. 2000; 356: 366–372.[CrossRef][Medline] [Order article via Infotrieve]

24. Neal B, MacMahon S, Chapman N. Effects of ACE inhibitors, calcium antagonists, and other blood-pressure-lowering drugs: results of prospectively designed overviews of randomised trials. Lancet. 2000; 356: 1955–1964.[CrossRef][Medline] [Order article via Infotrieve]

25. ALLHAT Officers and Coordinators for the ALLHAT Collaborative Research Group. Major outcomes in high-risk hypertensive patients randomized to angiotensin-converting enzyme inhibitor or calcium channel blocker vs diuretic. JAMA. 2002; 288: 2981–2997.[Abstract/Free Full Text]

26. Psaty BM, Heckbert SR, Koepsell TD, Siscovick DS, Raghunathan TE, Weiss NS, Rosendaal FR, Lemaitre RN, Smith NL, Wahl PW, Wagner EH, Furberg CD. The risk of myocardial infarction associated with antihypertensive drug therapies. JAMA. 1995; 274: 620–625.[Abstract/Free Full Text]

27. Palatini P, Casiglia E, Julius S, Pessina AC. High heart rate: a risk factor for cardiovascular death in elderly men. Arch Intern Med. 1999; 159: 585–592.[Abstract/Free Full Text]

28. Baxter GF, Sumeray MS, Walker JM. Infarct size and magnesium: insights into LIMIT-2 and ISIS-4 from experimental studies. Lancet. 1996; 348: 1424–1426.[CrossRef][Medline] [Order article via Infotrieve]

29. Mizushima S, Cappuccio FP, Nichols R, Elliott P. Dietary magnesium intake and blood pressure. J Hum Hypertens. 1998; 12: 447–453.[CrossRef][Medline] [Order article via Infotrieve]

30. Sakata K, Shirotani M, Yoshida H, Nawada R, Obayashi K, Togi K, Miho N. Effects of amlodipine and cilnidipine on cardiac sympathetic nervous system and neurohormonal status in essential hypertension. Hypertension. 1999; 33: 1447–1452.[Abstract/Free Full Text]

31. Yagi S, Goto S, Yamamoto T, Kurihara S, Katayama S. Effect of cilnidipine on insulin sensitivity in patients with essential hypertension. Hypertens Res. 2003; 26: 383–387.[CrossRef][Medline] [Order article via Infotrieve]

32. Varagic J, Susic D, Frohlich ED. Cilnidipine improves spontaneously hypertensive rat coronary hemodynamics without altering cardiovascular mass and collagen. J Hypertens. 2002; 20: 317–322.[CrossRef][Medline] [Order article via Infotrieve]

This article has been cited by other articles:

				R. M. Touyz Transient receptor potential melastatin 6 and 7 channels, magnesium transport, and vascular biology: implications in hypertension Am J Physiol Heart Circ Physiol, March 1, 2008; 294(3): H1103 - H1118. [Abstract] [Full Text] [PDF]

				R. Miranda-Ferreira, R. de Pascual, A. M. G. de Diego, A. Caricati-Neto, L. Gandia, A. Jurkiewicz, and A. G. Garcia Single-Vesicle Catecholamine Release Has Greater Quantal Content and Faster Kinetics in Chromaffin Cells from Hypertensive, as Compared with Normotensive, Rats J. Pharmacol. Exp. Ther., February 1, 2008; 324(2): 685 - 693. [Abstract] [Full Text] [PDF]

				N. M. Rummery, J. A. Brock, P. Pakdeechote, V. Ralevic, and W. R. Dunn ATP is the predominant sympathetic neurotransmitter in rat mesenteric arteries at high pressure J. Physiol., July 15, 2007; 582(2): 745 - 754. [Abstract] [Full Text] [PDF]

This Article Abstract Full Text (PDF) All Versions of this Article: 44/6/897    most recent 01.HYP.0000146536.68208.84v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Shimosawa, T. Articles by Fujita, T. Search for Related Content PubMed PubMed Citation Articles by Shimosawa, T. Articles by Fujita, T. Related Collections Hypertension - basic studies Ion channels/membrane transport Autonomic, reflex, and neurohumoral control of circulation