RUN-DOWN OF CALCIUM CURRENT IS RELATED TO INTRACELLULAR SODIUM

Run-down of Ca2+ current was studied in isolated ginuea pig ventricula r cells and it was found to be attenuated by intracellular sodium. Cal cium currents were recorded after activation of Na+ channels by a step pulse. The ''run-down'' in 30 min was significantly reduced compared with control cells. When NaCl (0.1-10 mM) diffused from the micropipet te into the cells, run-down of Ca2+ current was also signifcantly atte nuated. However, the resulted increase of intracellular Na+ did not af fect voltage dependent activation of Ca2+ current, but the duration of the action potential was shortened slightly. (C) 1994 Academic Press, Inc.