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

Abstract

Abstract. We analyzed [Ca 2+ ] i transients in Paramecium cells in response to veratridine for which we had previously established an agonist effect for trichocyst exocytosis (Erxleben & Plattner, 1994. J. Cell Biol. 127:935-945; Plattner et al., 1994. J. Membrane Biol. 158:197-208

Calcium in ciliated protozoa: Sources, regulation, and calcium-regulated cell functions

“…Interestingly, in Paramecium neomycin inhibits trichocyst exocytosis (Plattner et al, 1985b) and. as we found out much later, Ca 2 + influx (Klauke et al, 1999). By virtue of its charge and small size, neomycin may inhibit some plasmalemmal channel function, just as it inhibits internal InsPTactivated Ca 2t -release channels in mammalian cells.…”

“…. alkaloid, veratridine Plattner et al, 1994;Blanchard, 1998;Blanchard et al, 1999). Although it normally acts as a Na+ channel agonist, we have found evidence that it may cause stimulation by labilizing membranes, increasing their fluidity and resulting in increased Ca 2 + fluxes.…”

“…The first component can be seen at low [Ca 2 +]o or during the application of AED or store-mobilizing agents. like caffeine (Klauke and Plattner, 1998) or 4CmC (Klauke et al, 1999). Store mobilization alone causes only partial and slow activation of trichocyst exocytosis (Plattner et aI., 1997a).…”

“…For the Ca 2 + channels involved and a Ca 2 + sensor in the cell membrane, see Sections III.C.1 and III.C.2, respectively. Briefly, we assume that AED activates a Ca 2 +/(polyvalent cation)-sensing receptor (CaSR; Klauke et al, 1999), which activates ryanodine-receptortype Ca 2 +-release channels in alveolar sacs. This occurs without the involvement of any of the known second messengers (Uinge et al, 1995).…”

Polyamine Triggering of Exocytosis in Paramecium Involves an Extracellular Ca 2+ /(Polyvalent Cation)-Sensing Receptor, Subplasmalemmal Ca-Store Mobilization and Store-Operated Ca 2+ -Influx via Unspecific Cation Channels

“…Theoretically this should also hold for high [ [7]. We assume exocytosis inhibition by too long exposure (∼1 min) to high [Ca 2+ ] o , i.e., 10 mM, and we attribute this effect to the well established membrane stabilizing effect by Ca 2+ [22] caused by rigidification of membrane lipids in the course of equally well established Ca 2+ -mediated lipid phase transition [61].…”