Effects of Divalent Cations on the Excitability and on the Cytoplasmic Streaming of Chara corallina

The plasmalemma of Chara corallina remained excitable, whenit was treated with 1 to 100 µM of TFP. However, excitationcessation (EC) uncoupling, i.e. no cessation of cytoplasmicstreaming during an action potential, was observed in a concentrationrange of TFP between 30 to 100 µM. The percentage of occurrenceof the EC-uncoupling increased with the concentration of TFP.The EC-uncoupling effect of TFP could be removed by externalperfusion with 0.1 min or higher concentration of Ca²⁺ but notwith Mg²⁺, Ba²⁺, Sr²⁺ or Pb²⁺. These results suggest that excitationof the plasmalemma and EC-coupling is regulated via calmodulinor calmodulin-like system. (Received December 15, 1986; Accepted April 4, 1987)