Possible involvement of calmodulin in maturation and activation of Chaetopterus eggs

We report the isolation of calmodulin from oocytes of Chaetopterus pergamentaceus. The identification of this protein is based on (1) activation of beef heart cAMP phosphodiesterase, (2) heat stability, (3) sensitivity to chlorpromazine, and (4) electrophoretic mobility identical to that of porcine brain calmodulin after sodium dodecyl sulfate-polyacrylamide gel electrophoresis in the presence of either Ca2+ or EGTA. We treated oocytes with chlorpromazine and W-7 to investigate the involvement of calmodulin in meiosis initiation and egg activation. Very low concentrations of chlorpromazine inhibited germinal vesicle breakdown (GVBD). This effect was shown to be dependent upon bright indirect light, since the drug was much less effective at GVBD inhibition under conditions of very low illumination. Higher concentrations of chlorpromazine and W-7 (100 microM) inhibited GVBD and activated eggs with intact germinal vesicles as determined by fertilization envelope formation and the onset of ameboid activity. Neither egg activation nor inhibition of calmodulin stimulation of phosphodiesterase activity in vitro was affected by light. These results are consistent with a role for calmodulin in egg activation and GVBD, but suggest that chlorpromazine in bright light may prevent GVBD by some mechanism other than calmodulin inhibition.