Caffeine-Induced Ca 2+ Transients and Exocytosis in Paramecium Cells. A Correlated Ca 2+ Imaging and Quenched-Flow/Freeze-Fracture Analysis

Veratridine-Mediated Ca 2+ Dynamics and Exocytosis in Paramecium Cells

“…Any difference may yield important functional clues. For instance, nd9-28°C cells may show internal decondensation of trichocyst contents in response to a permeable agonist [27], as we found. The tl cells may show much more pronounced [Ca 2+ ] i transients which may much more rapidly spread towards the cell interior via unoccupied trichocyst docking sites, and this is in fact what we observed.…”

“…For both these agents we demonstrated, also by fluorochrome analysis, the occurrence of a cortical [Ca 2+ ] i transient orginating primarily from cortical pools ("alveolar sacs" [49]) and reinforced by superimposed Ca 2+ influx from the medium [14,15,26,27]. For trichocyst secretion induced by veratridine, the source of calcium is addressed in this paper.…”

“…In Paramecium, veratridine induces trichocyst exocytosis [15,29,36], though less efficiently than the polyamine secretagogue, aminoethyldextrane (AED) [35,38] or caffeine [15,27]. For both these agents we demonstrated, also by fluorochrome analysis, the occurrence of a cortical [Ca 2+ ] i transient orginating primarily from cortical pools ("alveolar sacs" [49]) and reinforced by superimposed Ca 2+ influx from the medium [14,15,26,27].…”

“…This involves membrane fusion and contents discharge ("decondensation" ‫ס‬ severalfold stretching of pear-shaped contents to needles during expulsion through exocytotic openings), [37,38]. Membrane fusion requires a subplasmalemmal [Ca 2+ ] i increase [14,15,26,27], while decondensation of contents, with no Ca detectable by x-ray microanalysis [45], requires access of Ca 2+ to the secretory materials [5]. This normally occurs by influx of Ca o 2+ after formation of an exocytotic pore [37,38].…”

“…Finally, nonsecretory mutants, nd9 and tl, were used also for technical reasons, since these cells, in contrast to 7S cells, are not vigorously dislocated during quasiexplosive trichocyst expulsion. Therefore, these strains, though mobile, are much more easily and reliably amenable to 2 fluorochrome analysis of calibrated [Ca 2+ ] i transients, while 7S cells can be preferably used for semiquantitative, but fast, 1 analysis on a subsecond time scale [14,26,27].…”