Endothelium-dependent vascular control via membrane potential

Abstract

Besides secreting vasoactive substances such as nitric oxide and endothelin, vascular endothelial cells control the vascular tone through affecting the membrane potential of smooth muscle cells. Actually the vessel diameter is sensitive to the membrane potential. The smooth muscle and endothelial cells are electrically coupled with the myoendothelial gap junctions and they share a membrane potential and an intracellular ionic environment. In fact, the resting membrane potentials of both cells are quite similar, being around -50 mV, with the smooth muscle cells slightly more negative than the endothelial cells. Once separated from the smooth muscle cells, the endothelial cells cannot maintain their membrane polarization. So, two kinds of cells are functioning as a unit in terms of the membrane potential, and irrespective of which kind of cells is stimulated, the membrane potentials are changed in both kinds of cells. For example, ACh increases endothelial [Ca²⁺]_i, which in turn activates charybdotoxin-sensitive IK_Ca, apamin-sensitive SK_Ca and Cl_Ca channels in the endothelium. Resulting membrane responses vary between preparations from a sustained hyperpolarization to a transient hyperpolarization followed by a depolarization, and a variability in [Cl⁻]_i may be one of the reasons for the variations. [J Physiol Sci. 2007;57 Suppl:S7]