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(Hypertension. 2003;41:1124.)
© 2003 American Heart Association, Inc.

Scientific Contribution

Mislocalization of eNOS and Upregulation of Cerebral Vascular Ca²⁺ Channel Activity in Angiotensin-Hypertension

Volodymyr Gerzanich; Svetlana Ivanova; Hui Zhou; J. Marc Simard

From the Departments of Neurosurgery (V.G., S.I., H.Z., J.M.S.), Physiology (J.M.S.), and Pathology (J.M.S.), University of Maryland School of Medicine, Baltimore.

Correspondence to Dr J. Marc Simard, Department of Neurosurgery, University of Maryland School of Medicine, 22 S Greene St, Baltimore, MD 21201-1595. E-mail msimard{at}surgery1.umaryland.edu

We tested the hypothesis that endothelial dysfunction induced by angiotensin II (Ang-hypertension) would impair regulatory control of vascular smooth muscle L-type Ca²⁺ channels by endothelial nitric oxide synthase (eNOS). We studied cerebral lenticulostriate arterioles (LSAs) from control rats, from rats infused with Ang (240 µg · kg^-1 · h^-1 SQ x4 days), which were normotensive, and from Ang-hypertensive rats (AHR; 240 µg · kg^-1 · h^-1 x28 days). Patch-clamp measurements on isolated LSA smooth muscle cells (SMCs) showed a significant increase in Ca²⁺ channel availability with 4- and 28-day infusions versus controls (0.47±0.03 and 0.66±0.05 vs 0.36±0.03 pS/pF, respectively; P<0.01), with Western blots showing no change in channel protein expression, consistent with altered channel regulation. In LSAs from 28-day AHR, 4,5-diaminofluorescein diacetate imaging showed diminished NO production in response to acetylcholine stimulation in vivo, and inhibition of eNOS with N^G-nitro-L-arginine methyl ester failed to increase Ca²⁺ channel availability in isolated SMCs, indicating an abnormality with the eNOS/NO-signaling pathway regulating the channel. Immunofluorescence imaging showed that in 1 of 53, 33 of 109, and 53 of 62 LSAs from controls and from rats with 4- and 28-day infusions, respectively, eNOS was absent from its normal location at the abluminal border and was mislocalized to perinuclear Golgi. Ca²⁺ channel availability in LSA SMCs from controls and from rats with 4- and 28-day infusions was proportional to the fraction of LSAs showing eNOS mislocalization, but not blood pressure. These data provide the first evidence linking Ang-induced eNOS mislocalization, eNOS dysfunction, and Ca²⁺ channel upregulation, and they provide novel mechanistic insights into pathological changes in LSAs associated with stroke.

Key Words: calcium channels • angiotensin II • nitric oxide synthase • hypertension, experimental • muscle, vascular, smooth • endothelium

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