摘要：

Ca 2+ dependent exocytosis in Paramecium involves the release of numerous secretory organelles known as "trichocysts". According to Garofalo et al . (1983) trichocysts pass through three stages of condensed (tmxI), partially expanded (stage II) before release, and fully expanded (stage III) or released trichocysts. We have therefore investigated the effect of two widely used Ca 2+ channel blockers, verapamil and nifedipine and the muscular relaxant, dantrolene-Na, on the process of trichocyst release. Verapamil and nifedipine inhibited secretion in a dose dependent manner, but dantrolene-Na and the solvent, PEG-400, did not abolish it. Electron microscopic study of preincubated Paramecium cells in verapamil resulted in the appearance of tmxI, whereas untreated controls remained in partially expanded stage II. Pretreatment of isolated membrane free trichocysts with verapamil did not inhibit matrix expansion in the presence of increasing Ca 2+ concentration. In a separate experiment, cells were pretreated with verapamil and the anti calmodulin compound, trifluoperazine. The cells were then induced to release their secretory contents by picric acid-Ca 2+ treatment. Electron microscopic examination of cells captured by quick fixation with osmium tetroxide revealed that verapamil treated cells manifested the inhibition of membrane fusion, whereas in TFP treated cells there was no sign of a traceable exocytotic opening formation after membrane fusion. Based on present results we propose a role for calmodulin in the formation of exocytotic openings.

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