Calmodulin and Ca2+-controlled cytoplasmic streaming in Characean cells.

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Abstract
The presence of calmodulin (CaM) was demonstrated in the homogenate of Chara australis internodal cells by the radioimmunoassay method. It amounted to 400 ng per ml homogenate. The possible involvement of CaM in cytoplasmic streaming was examined by applying CaM-binding drugs to intact cells and plasmalemma-permeabilized cells. Thirty .mu.M of trifluoperazine (TFP) applied to intact Chara cells did not interfere with the cessation of streaming accompanying membrane excitation, which causes a transient increase in cytoplasmic Ca2+ concentration. After a long exposure to TFP, the action potential resulted in an irreversible depolarization and inhibited the recovery of streaming due to loss of the semipermeability of the plasma membrane. In permeabilized cells, neither the motile system nor the Ca2+-induced cessation was inhibited by TFP up to 100 .mu.M, by fluphenazine (FPH) at 1 .mu.M, or by N-(6-aminohexyl)-5-chloro-1-naphthalene sulfonamide (W-7) at 10 .mu.M. However, the recovery of streaming induced by washing away the Ca2+ was completely inhibited by these drugs. On the other hand, these drugs did not affect the streaming of tonoplast-free cells, irrespective of the presence or absence of 10 .mu.M Ca2+. Thus cytoplasmic streaming is controlled by two Ca2+-sensitizing components, one related to the streaming cessation and the other, probably CaM, related to recovery. FPH at 50 .mu.M or W-7 at 100 .mu.M, even in the absence of Ca2+, stopped the cytoplasmic streaming of permeabilized cells. Washing away the drugs did not lead to streaming recovery after W-7 treatment, but sometimes did after FPH treatment.