ENDOTHELIUM-DEPENDENT HYPERPOLARIZATION - A ROLE IN THE CONTROL OF VASCULAR TONE

Endothelial-dependent relaxation of vascular smooth muscle cells evoke d by a number of agonists, including cholinomimetics and substance P, is often accompanied by an increase (repolarization and/or hyperpolari zation) in the membrane potential. This change in membrane potential a ppears predominately to reflect the action of an endothelial-derived h yperpolarizing factor (EDHF), which is distinct from NO (or endothelia l-derived relaxing factor), and is discussed in this article by Chris Garland and colleagues. In large conducting arteries, EDHF may provide a secondary system to NO, which assumes primary importance in some di sease states such as pulmonary hypertension and atherosclerosis. Howev er, in small resistance arteries (100-300 mu m), EDHF appears to be a major determinant of vascular calibre under normal conditions, and may therefore be of primary importance in the regulation of vascular resi stance.