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Journal of Experimental Biology 88,293-304 (1980)
Published by Company of Biologists 1980

Ca-Induced K⁺-Outward Current in Paramecium Tetraurelia

YOUKO SATOW ¹ and CHING KUNG ¹

¹ Laboratory of Molecular Biology and Department of Genetics, University of Wisconsin, Madison, Wisconsin 53706 U.S.A.

Late K-outward currents upon membrane depolarization were recorded in Paramecium tetraurelia under a voltage clamp. A Ca-induced K-outward component is demonstrated by subtracting the value of the outward current in a pawn A mutant lacking functional Ca-channels (pwA₅₀₀). The Ca-induced K-outward current activates slowly, reaching a peak after 100 to 1000 ms. The current then remains steady or reaches the steady state after a decline of several seconds.

EGTA^2- injection experiments show that the Ca-induced K-outward current is dependent on the internal Ca²⁺ concentration. The current is shown to depend on the voltage-dependent Ca conductance, by study of the leaky pawn A mutant (pwA₁₃₂), which has a lowered Ca conductance as well as a lowered Ca-induced K-current. The Ca-induced G_K is thus indirectly dependent on the voltage. The maximal G_K is about 40 nmho/cell at + 7 mV in 4 mM-K⁺.

The Ca-induced K current is sustained throughout the prolonged depolarization and the prolonged ciliary reversal.

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