CALCIUM-DEPENDENCE OF THE CALCIUM-ACTIVATED CHLORIDE CURRENT IN SMOOTH-MUSCLE CELLS OF RAT PORTAL-VEIN

Ca2+-activated Cl- current in freshly isolated smooth muscle cells from rat portal vein was studied using the whole-cell patch-clamp technique. Simultaneously, the free-cytosolic Ca2+ concentration (Ca(i)) was estimated using emission from the dye Indo-1. Pretreatment of the cells with amytal and carbonyl-cyanide-m-chlorophenylhydrazone, which reduced the intracellular adenosine triphosphate concentration, was used to weaken the cellular Ca2+ homeostatic system. Ca(i) of treated cells slowly increased during perfusion with an external Ca2+-containing solution. This rise in Ca(i) gradually activated a Ca2+-dependent Cl- current which allowed the study of the relationship between activation of this current and Ca(i) levels. The threshold Ca(i) for activation of Cl- channels was around 180 nM and full activation occurred at 600 nM. The Ca(i) dependence of the Cl- channels was not changed during application of noradrenaline and did not depend on the membrane potential. The gating of Ca2+-dependent Cl- channels of rat portal vein myocytes seems to be mainly controlled by intracellular Ca2+.