COLD-INDUCED DECREASE OF K-7, IN PARAMECIUM-TETRAURELIA( CONDUCTANCE AND ITS INHIBITION BY A CALMODULIN ANTAGONIST, W)

Under voltage clamp, Paramecium tetraurelia was used to examine the co ld-induced inward current and its inhibition by a calmodulin antagonis t, 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 r esting potential, and it was significantly blocked by using CsCl-fille d electrodes and tetraethylammonium in the bath solution, suggesting t hat the current was accompanied mainly by a decrease in K+ conductance . The cold-induced inward current was reversibly inhibited by the exte rnal application of W-7 in a concentration-dependent manner. EGTA-micr oinjection into the cell also reduced the current. These results indic ate that the decrease in K+ conductance induced by cooling is Ca2+-dep endent and is inhibited by W-7.