Regulation of vascular tone, molecular mechanisms.

V ASCULAR tone, a state of maintained contraction of the smooth muscle in the vessel wall, is the process by which the blood vessel carries out its physiologic functions, its pharmacologic responses, and its pathologic changes. Current research directed at an understanding of the molecular mechanisms that regulate vascular tone is progressing at a rapid rate. The state of this art was surveyed in 1980 by the American Physiological Society’s 686-page Physiology Handbook, Section 2, Volume II, “Vascular Smooth Muscle.” The current review should satisfy those who have in mind a less extensive compilation of information. It also describes new pieces of the puzzle that have been found since the Handbook went to press over a year ago. In the broadest sense, pieces of this puzzle are sought to complete two quite different pictures, both depicting the affairs of calcium. The first deals with the role of calcium in the regulation of the contractile proteins; the second with the function of cell membranes in the regulation of myoplasmic calcium concentration.