Contribution of Calcium Influx on Trichocyst Discharge in Paramecium caudatum(Cell Biology)(<SPECIAL ISSUE>Origin and evolution of chordates)

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Trichocyst discharge in Paramecium spp. is known to be mediated by rapid exocytosis. Applied stimuli induce fusion of the trichocyst membrane and plasma membrane within 30 ms. Both Ca^<2+> release from intracellular store (s) and Ca^<2+> influx from extracellular region have been suggested to be related to the trichocyst discharge. We constructed a new system in which to record intracellular levels of Ca^<2+> ([Ca^<2+>]_i) and microscopic images simultaneously without changing the optical path. With this system, we recorded [Ca^<2+>]_i at 2 ms intervals and microscopic images of trichocyst discharge at video rate (33 ms intervals) simultaneously in Paramecium caudatum. Simultaneous application of Ca^<2+> chelator at 100 mM with secretagogue onto Paramecium cells resulted in only a slight increase in [Ca^<2+>]_i (Δ[Ca^<2+>]_i). Furthermore, no extrusion of trichocysts occurred. In contrast, application of secretagogue concomitant with Ca^<2+> chelator at 20 mM induced a Δ[Ca^<2+>]_i composed of two phases. In this case, extrusion of trichocysts occurred. These observations directly indicated that Ca^<2+> influx from the extracellular medium in addition to Ca^<2+> release from intracellular store (s) contributes to Δ[Ca^<2+>]_i during trichocyst discharge.
社団法人日本動物学会の論文
2001-05-20