Heme oxygenase-mediated vasodilation involves vascular smooth muscle cell hyperpolarization

Area of Science:

• Cardiovascular Physiology
• Vascular Biology
• Hypoxia Research

Background:

• Chronic hypoxia is linked to reduced vascular reactivity.
• Heme oxygenase (HO)-derived carbon monoxide (CO) is implicated but its vasodilation mechanism is unknown.
• Understanding CO's role is crucial for managing hypoxia-related vascular dysfunction.

Purpose of the Study:

• To elucidate the mechanism of endogenous carbon monoxide (CO)-mediated vasodilation in chronic hypoxia.
• To investigate the role of specific ion channels and signaling pathways in CO-induced vasodilation.

Main Methods:

• Isolated pressurized mesenteric arterioles from chronically hypoxic rats were used.
• Heme-l-lysinate (HLL), an HO substrate, was administered to induce endogenous CO production.
• Vascular smooth muscle (VSM) membrane potential and vasodilatory responses were measured using various inhibitors (iberiotoxin, ODQ, ryanodine) and spin traps.

Main Results:

• Heme-l-lysinate (HLL) induced dose-dependent vasodilation, largely blocked by iberiotoxin.
• HLL caused VSM cell hyperpolarization, sensitive to zinc protoporphyrin IX and iberiotoxin.
• Exogenous CO vasodilation was inhibited by iberiotoxin and ODQ, suggesting a role for K+ channels.

Conclusions:

• Endogenous CO-mediated vasodilation involves the cGMP-independent activation of large-conductance Ca2+-activated K+ channels (BK channels).
• This pathway does not appear to involve ryanodine-sensitive Ca2+ stores or Ca2+ sparks.
• Findings clarify a key mechanism in vascular adaptation to chronic hypoxia.