Inhibition of trichocyst exocytosis and calcium influx in Paramecium by amiloride and divalent cations.
Regulated exocytosis of defensive secretory organelles, the trichocysts, as well as a transient Ca(2+)-influx can be induced in Paramecium by aminoethyldextran (Kerboeuf and Cohen, J Cell Biol (1990) 111, 2527). Knoll et al (Febs Lett (1992) 304, 265) reported that veratridine was also a secretagogue for Paramecium. Here we show that, like aminoethyldextran, veratridine induces a transient Ca(2+)-influx. Both aminoethyldextran- and veratridine-induced exocytosis and associated Ca(2+)-influx were: i) blocked in the ndl2 thermosensitive mutant at the non-permissive temperature; and ii) inhibited by amiloride and four divalent cations, Ba2+, Mg2+, Sr2+ and Co2+. This suggests that, although of different chemical nature, aminoethyldextran and veratridine act through the same physiological pathway. In addition, the inhibitory doses are comparable to the ones found to inhibit a hyperpolarization-sensitive Ca(2+)-current described in Paramecium (Preston et al (1992) J Gen Physiol 100, 233). The possibility that the activation of this Ca(2+)-current by the secretagogue represents an early step in the regulation of trichocyst exocytosis is discussed.
Kerboeuf
D
D
Centre de Génétique Moléculaire, l'Université Pierre et Marie Curie, Gif-sur-Yvette, France.
Cohen
J
J
D000584:Amiloride / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002413:Cations, Divalent / Q000494:pharmacology*; D004232:Diuretics / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005089:Exocytosis / Q000187:drug effects*; D010247:Paramecium / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D014701:Veratridine / Q000494:pharmacology
D002121:Calcium Channel Blockers; D002413:Cations, Divalent; D004232:Diuretics; D014701:Veratridine; D000584:Amiloride; D002118:Calcium