Secretory organelles of Paramecium cells (trichocysts) are not remarkably acidic compartments.

Abstract

Acridine orange (AO) trapping in conjunction with fluorescence microscopy was applied toPammecium cells. Trichocysts were not labeled when analyzed with an image intensification system (as opposed to a lysosomal population). Only with increasing intensity of ultraviolet light (UV) did trichocysts (and to some extent the cytosol) exhibit orange fluorescence, both effects being paralleled by inaeasing cell damage. Therefore, in comparison with the reported cytosolic pH (6.8), trichocysts cannot be considered as essentially acidic compartments. This is supported by experiments in vitro, using isolated cortex fragments or isolated fractions of membrane-bounded trichocysts (390% non-leaky). Again, during w illumination orange fluorescence was observed even in the absence of ATP and Mg2'. Furthermore, this A0 fluorescence and the condensation state of trichocyst contents were not affected by N H 3 or by any of the widely differing ion-and H+-exchange inhibitors or ionophores tested. Decondensation of trichocyst contents occurred only when Ca2+ ionophore A23187 or X537A was incorporated into trichocyst membranes and when Ca2+ was then added. In this case all trichocysts partially decondensed within their intact membranes. We conclude that A 0 might be trapped in trichocysts by the abundant acidic secretory components during observation with uv light, rather than by acidic luminal pH. ( J Hisrochem Cyrochem 40953-160, 1992)

γ-Amino butyric acid (GABA) release in the ciliated protozoonParameciumoccurs by neuronal-like exocytosis

“…Residue numbers are indicated at the left. Lumpert et al, 1992). Our release and confocal microscopy experiments, performed with bafilomycin A1-pretreated Paramecium cells, not only showed a significant reduction of GABA release induced by depolarization but also a less efficient storage of GABA in the vesicular compartment.…”

Distinct Subcellular Localization of a Group of Synaptobrevin-Like SNAREs in Paramecium tetraurelia and Effects of Silencing SNARE-Specific Chaperone NSF

“…The PtSyb5-positive type is possibly related to trichocyst biogenesis for the following reasons. (i) These structures are not remarkably acidic (42), just like mature trichocysts and their precursor compartments (22).…”

Proteolytic Processing and Ca2+-binding Activity of Dense-Core Vesicle Polypeptides inTetrahymena

“…In the case of the conversion of proGrl1p to Grl1p, one solution would be to make processing itself a calcium-regulated step: the protease(s) could be inhibited at calcium concentrations high enough to trigger expansion. Although pH might also be a regulatory factor, ciliate granules do not appear to be acidified (Garreau de Loubresse et al, 1994;Lumpert et al, 1992). A working hypothesis, presented in Figure 13, illustrates a putative mechanism for step-wise coordination of a set of interactions.…”