title: 48-h Hypoxic exposure results in endothelium-dependent systemic vascular smooth muscle cell hyperpolarization.
abstract: Chronic hypoxia (CH) results in reduced sensitivity to vasoconstrictors in conscious rats that persists upon restoration of normoxia. We hypothesized that this effect is due to endothelium-dependent hyperpolarization of vascular smooth muscle (VSM) cells after CH. VSM cell resting membrane potential was determined for superior mesenteric artery strips isolated from CH rats (PB = 380 Torr for 48 h) and normoxic controls. VSM cells from CH rats studied under normoxia were hyperpolarized compared with controls. Resting vessel wall intracellular Ca(2+) concentration ([Ca(2+)](i)) and pressure-induced vasoconstriction were reduced in vessels isolated from CH rats compared with controls. Vasoconstriction and increases in vessel wall [Ca(2+)](i) in response to the alpha(1)-adrenergic agonist phenylephrine (PE) were also blunted in resistance arteries from CH rats. Removal of the endothelium normalized resting membrane potential, resting vessel wall [Ca(2+)](i), pressure-induced vasoconstrictor responses, and PE-induced constrictor and Ca(2+) responses between groups. Whereas VSM cell hyperpolarization persisted in the presence of nitric oxide synthase inhibition, heme oxygenase inhibition restored VSM cell resting membrane potential in vessels from CH rats to control levels. We conclude that endothelial derived CO accounts for persistent VSM cell hyperpolarization and vasoconstrictor hyporeactivity after CH.
authors.affiliation: Vascular Physiology Group, Department of Cell Biology and Physiology, University of New Mexico Health Sciences Center, 915 Camino de Salud, Albuquerque, NM 87131-5218, USA. searley@unm.edu
authors.forename: Scott
authors.initials: S
authors.lastname: Earley
authors.forename: Jay S
authors.initials: JS
authors.lastname: Naik
authors.forename: Benjimen R
authors.initials: BR
authors.lastname: Walker
mesh_terms: D000818:Animals; D004594:Electrophysiology; D004730:Endothelium, Vascular / Q000503:physiopathology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006419:Heme Oxygenase (Decyclizing) / Q000037:antagonists & inhibitors; D000860:Hypoxia / Q000503:physiopathology*; D066298:In Vitro Techniques; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000201:enzymology / Q000473:pathology / Q000503:physiopathology*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D052250:Nitric Oxide Synthase Type III; D019335:Nitroarginine / Q000494:pharmacology; D011524:Protoporphyrins / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
chemical_list: D004791:Enzyme Inhibitors; D011524:Protoporphyrins; C017803:zinc protoporphyrin; D019335:Nitroarginine; D019001:Nitric Oxide Synthase; D052250:Nitric Oxide Synthase Type III; C496316:Nos3 protein, rat; D006419:Heme Oxygenase (Decyclizing)