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Pflügers Archiv

, Volume 439, Issue 6, pp 752–758 | Cite as

Functional integrity of endothelium determines Ca2+ channel availability in smooth muscle: involvement of nitric oxide

  • J.M. Simard
  • X. Li
Original Article

Abstract

Endothelium regulates smooth muscle contractility in part via nitric oxide (NO). We tested the hypothesis that endothelial dysfunction, either produced by injury or simulated pharmacologically by reducing the bioavailability of NO, results in elevated Ca2+ channel availability (ng max=maximum conductance/cell capacitance) in smooth muscle cells isolated from the vessel. Using basilar arteries of normotensive Wistar rats, we measured ng max in smooth muscle cells from control vessels, from vessels in which endothelium was injured using Na fluoroscene plus light, and from vessels in which the bioavailability of NO was reduced by pretreatment with the NO scavenger 1H-imidazol-1-yloxy,2-(4-carboxyphenyl)-4,5-dihydro-4,4,5,5-tetramethyl-3-oxide, potassium salt (C-PTIO), or the endothelial nitric oxide synthase (eNOS) inhibitor N G-nitro-l-arginine methyl ester (l-NAME). Values of ng max in these four groups of cells were 0.28±0.02 nS/pF (n=22), 0.51±0.05 nS/pF (n=15), 0.43±0.03 nS/pF (n=12), and 0.47±0.04 nS/pF (n=14) (P<0.05, ANOVA), respectively. To determine whether larger currents associated with endothelial dysfunction exhibit altered sensitivity to exogenous NO, we quantified the response to various concentrations of NO donor, Na nitroprusside (SNP), in 37 cells from control vessels and 33 cells from vessels pretreated with l-NAME. SNP exhibited identical potency (half-maximum values, 18.7 and 21.1 nM) but greater apparent efficacy (maximum fractional block, 0.82 versus 0.63) in downregulating Ca2+ channel currents in cells isolated from vessels with dysfunctional endothelium. Our results are consistent with a direct influence of endogenous NO on Ca2+ channel availability in smooth muscle cells, and indicate that Ca2+ channel availability in isolated smooth muscle cells may be a sensitive measure of the functional integrity of the endothelium in the parent vessel.

Ca2+ channel Electron microscopy Endothelium Hypertension Nitric oxide Patch clamp Vascular smooth muscle 

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Copyright information

© Springer-Verlag 2000

Authors and Affiliations

  • J.M. Simard
    • 1
  • X. Li
    • 1
  1. 1.Department of Neurosurgery, University of Maryland School of Medicine, 22 South Greene Street, Baltimore MD 21201USA

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