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Vascular Physiology Group, Department of Cell Biology and Physiology, University of New Mexico Health Sciences Center, Albuquerque, New Mexico 87131-5218
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 Ca2+ concentration
([Ca2+]i) and pressure-induced
vasoconstriction were reduced in vessels isolated from CH rats compared
with controls. Vasoconstriction and increases in vessel wall
[Ca2+]i in response to the
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
[Ca2+]i, pressure-induced vasoconstrictor
responses, and PE-induced constrictor and Ca2+ 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.
rat; carbon monoxide; calcium imaging; vasoreactivity
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