Myoendothelial electrical coupling in arteries and arterioles and its implications for endothelium-derived hyperpolarizing factor.

1. Considerable progress has been made over the past decade in evaluating the presence of electrical coupling between the endothelial and smooth muscle layers of blood vessels, prompted, in part, by ultrastructural evidence for the presence of myoendothelial junctions. 2. In a variety of vessels ranging in size from conduit arteries down to small arterioles, action potentials have been recorded from endothelial cells that were associated with constriction of the vessels and/or occurred in synchrony with and were indistinguishable from action potentials recorded from the smooth muscle. From these results, it is now firmly established that myoendothelial electrical coupling occurs in at least some blood vessels. 3. Spread of hyperpolarizing current from the endothelium to the smooth muscle is the most likely explanation of the smooth muscle hyperpolarization attributed to endothelium-derived hyperpolarizing factor. Because this hyperpolarization can evoke considerable relaxation of the smooth muscle, myoendothelial electrical coupling has important implications for endothelial regulation of the contractile activity of blood vessels.