Regulation of vascular tone by endothelium-derived hyperpolarizing factor

Area of Science:

• Cardiovascular Physiology
• Vascular Biology
• Molecular Pharmacology

Background:

• Endothelium-derived hyperpolarizing factor (EDHF) contributes to nitric oxide (NO)-independent vasodilation.
• Understanding the relationship between membrane potential and vascular tone is crucial for elucidating mechanisms of blood flow regulation.

Purpose of the Study:

• To investigate the quantitative relationship between membrane potential changes and vascular tone in rat mesenteric arteries.
• To compare the vasodilatory effects of EDHF, NO, and pinacidil in relation to membrane potential changes.

Main Methods:

• Simultaneous recording of membrane potential using intracellular microelectrodes and isometric tension in isolated rat mesenteric artery segments.
• Pharmacological manipulation using high potassium solutions, noradrenaline, acetylcholine, N omega-nitro-L-arginine, and pinacidil.
• Analysis of the correlation between membrane potential shifts and changes in vascular tone.

Main Results:

• Rat mesenteric arteries exhibit high sensitivity to membrane potential changes between -46 mV and -20 mV, with a 1 mV depolarization increasing tone by approximately 4%.
• EDHF-mediated relaxation was directly correlated with hyperpolarization, where 1 mV hyperpolarization corresponded to a 4.3% decrease in tone.
• Nitric oxide (NO) and pinacidil induced greater relaxation than EDHF at similar hyperpolarization levels, and their relaxations were not directly correlated with membrane potential changes.

Conclusions:

• Vascular tone in rat mesenteric arteries is highly sensitive to membrane potential within a critical depolarized range.
• EDHF's vasodilatory effect is primarily attributable to its hyperpolarizing action on the vascular smooth muscle.
• While NO and pinacidil also cause hyperpolarization, their relaxant effects are not solely explained by membrane potential changes, suggesting additional mechanisms are involved.