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Biol Bull 170: 43-50. (February 1986)
© 1986 Marine Biological Laboratory
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INHIBITION OF GERMINAL VESICLE BREAKDOWN AND ACTIVATION OF CYTOPLASMIC CONTRACTILITY IN SPISULA OOCYTES BY CALMODULIN ANTAGONISTS

ALAN G. CARROLL 1 and WILLIAM R. ECKBERG 2

1 Department of Biology, Indiana University-Purdue University at Indianapolis, Indianapolis, Indiana 46223
2 Department of Zoology, Howard University, Washington, DC 20059, and Marine Biological Laboratory, Woods Hole, Massachusetts 02543

We have treated Spisula oocytes with the calmodulin antagonists, chlorpromazine, calmidazolium, and W-7, and the inactive W-7 analog, W-5, to examine the role of calmodulin in meiosis reinitiation and egg activation in this species. Chlorpromazine and W-7 both inhibited germinal vesicle breakdown (GVBD) at 50-75 µM, whether triggered parthenogenetically by KCl activation or by fertilization. Calmidazolium was effective at ca. 3 µM. W-5 was ineffective. However, none of the anticalmodulin drugs inhibited GVBD when induced by ionophore A23l87. Time course studies showed that W-7 was effective at inhibiting KCl-induced GVBD only when added within 1 min after KCl. Similar studies using the calcium channel blocker, verapamil, showed that the period during which calcium channels are required for GVBD substantially exceeds the interval of sensitivity to W-7. Calmodulin thus acts at a stage prior to the calcium flux known to be required for GVBD.

Chlorpromazine, calmidazolium, and W-7 triggered ameboid contractions of the immature oocyte in addition to inhibiting GVBD. W-5 was again ineffective. The ameboid contractions observed are not typical of parthenogenetically activated oocytes of this species. Experiments in which chlorpromazine-treated oocytes were simultaneously treated with low concentrations of cytochalasin B showed that the cytoplasmic contractions are microfilament-dependent. The results indicate that the contractions triggered by the calmodulin antagonists are not a part of the normal egg activation process and that cytoplasmic contractions can be induced in this species independently of egg activation and may result from perturbation of a calmodulin-microfilament interaction.

Submitted on August 12, 1985
Accepted on October 31, 1985






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Copyright © 1986 by the Marine Biological Laboratory.