[Vanadate and smooth muscles].

Vanadate is a trace element in biological tissues which has inhibitory actions on various enzymes. It inhibits Na, K-ATPase of smooth muscle membrane. Ca-ATPase and Ca-uptake of membranous systems of smooth muscle cells are also inhibited by vanadate. Vanadate induces contractions in various smooth muscles. These contractions are not mediated by the inhibition of Na, K-ATPase. The contractions are induced by both the influxed Ca from extracellular space and the released Ca from intracellular binding sites. In certain smooth muscles, the changes in electrical activities are also involved. These effects of vanadate are not mediated by the release of transmitter from intrinsic nerves. The direct actions on contractile proteins is inhibitory and cannot be the cause of the contraction. Thus, vanadate induces contraction in various smooth muscles, by increasing Ca permeability of cell membrane and by releasing intracellular bound Ca. In addition, the inhibition of Ca-pump may also be involved in the initiation or potentiation of contraction by vanadate. The degree of each action varies among various smooth muscles.