Contribution of active membrane processes to conducted hyperpolarization in arterioles of hamster cheek pouch

Objective: Conduction of vasodilation triggered by acetylcholine (ACh) in arteriolar networks reflects hyperpolarization and its spread from cell to cell along the vessel wall. The amplitude and distance of the vasomotor response appear greater than can be explained by simple passive decay of the electrical signal. The authors tested the hypothesis that the conduction of hyperpolarization involves active membrane processes as the signal travels along the arteriolar wall. Methods: Intracellular recordings of membrane potential were made from either the smooth muscle or endothelial cell layer of arterioles of the hamster cheek pouch in vivo. Acetylcholine was delivered onto an arteriole using microiontophoresis at defined distances from the recording site, and transient hyperpolarizations were recorded. The area enclosed by the transients (voltage x time integral below baseline) was measured and compared to the area expected if the hyperpolarization was spreading passively. Results: In 11 of 15 recordings from smooth muscle and 5 of 7 from endothelium, areas of the transients were larger than expected for purely passive spread of the electrical signal. Conclusions: Conduction of hyperpolarization is enhanced by active membrane processes as the signal travels along the arteriolar wall. Signal augmentation will promote blood flow to tissue regions from which hyperpolarization of arterioles originates.