Activation of K^+-Channel in Membrane Excitation of Nitella axilliformis

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Two processes of the K^+ channel activation in plasma membrane excitation are suggested for Nitella axilliformis. One is related to the repolarizing process in the action potential and the other to the after-hyperpolarization (AH). Extra- and intracellular tetraethylammonium (TEA^+) and extracellular CO^<2+> prolonged the action potential, indicating involvement of K^+ channel activation in the repolarizing process of the action potential. The following findings showed that AH is caused by K^+ channel activation. First, AH was inhibited by extracellular K^+ and Rb^+ but not by Na^+ and Li^+. Second, it was not inhibited by intracellular TEA^+ but by extracellular TEA^+. Third, the membrane conductance increased during AH. Generation of AH was dependent on the level of the resting membrane potential [(E_m)_<REST>] which is affected by the activity of the electrogenic H^+ pump. AH was generated, when (E_m)_<REST> was more positive than a critical value, which was supposed to be the equilibrium potential for k^+ across the plasma membrane. Since extracellular Ca^<2+> competed with extracellular TEA+ and CO^<2+> in prolonging the action potential, and sometimes in inhibiting AH, Ca^<2+> may be involved in the k^+ channel activation.
日本植物生理学会の論文