[Calcium current and electromechanical coupling in the smooth muscle cells of the stomach].

The relationship between inward current and contraction was studied with double sucrose gap technique and measurement of contraction of the small muscular bundle in circular muscle from the fundus of guinea pig stomach. In voltage-clamped circular muscle, an inward current observed during depolarizing potential step was sensitive to Cd2+ or low external Ca2+ and had two components: a transient and a steady-state ones. Inactivation of this current was both voltage-dependent and Ca-current-dependent. Transient inward current activated phasic contraction, while the steady-state current activated tonic contraction. The voltage--dependence of the steady-state inward current was estimated with the Hodgkin--Huxley equation.