Cold-induced decrease of K+ conductance and its inhibition by a calmodulin antagonist, W-7, in Paramecium tetraurelia

Under voltage clamp, Paramecium tetraurelia was used to examine the cold-induced inward current and its inhibition by a calmodulin antagonist, W-7 [N-(6 aminohexyl)-5-chloro-1-naphthalenesulphonamide]. Cooling of the cell caused an inward current. The amplitude of the current was increased as the membrane potential was made more positive than the resting potential, and it was significantly blocked by using CsCl-filled electrodes and tetraethylammonium in the bath solution, suggesting that the current was accompanied mainly by a decrease in K+ conductance. The cold-induced inward current was reversibly inhibited by the external application of W-7 in a concentration-dependent manner. EGTA-microinjection into the cell also reduced the current. These results indicate that the decrease in K+ conductance induced by cooling is Ca(2+)-dependent and is inhibited by W-7.