Selective inhibition of the tonic component of potassium contracture of smooth-muscle cells in the portal vein by verapamil

Abstract

Experiments were carried out on smooth-muscle cells of the rat portal vein by the double sucrose gap method. Verapamil in concentrations of 1·10−9–1·10−7M was shown to block the tonic component of the potassium contracture selectively. Since under these circumstances potassium depolarization of the membrane was preserved, this is evidence that verapamil has a specific effect on the coupling of excitation with contraction, by blocking the passive inflow of calcium into the muscle cells. In higher concentrations (1·10−6–1·10−5M) verapamil inhibits the phasic component of potassium contracture, by blocking potential-dependent calcium channels of the membrane of the portal vein smooth-muscle cells responsible for action potential generation.