Presence of molecules related to the cholinergic system inParamecium primaurelia(Protista, Ciliophora) and possible role in mating pair formation: An experimental study

Abstract

Cholinergic-like molecules were, for the first time, detected both in mating-competent and immature cells of Paramecium primaurelia. By histochemical and immunohistochemical methods, acetylcholinesterase activity was localized on the cell surface of mating-competent cells and in the cytoplasm of immature cells. In mating-competent cells, molecules immunologically related to muscarinic acetylcholine (Ach) receptors were detected by immunofluorescence, and Ach nicotinic receptor-like molecules were revealed as α-bungarotoxin–binding sites. Aiming at verifying whether cholinergic-like molecules were involved in mating pair formation, we incubated mating-competent cells in vivo with 10-2 M AchCl; with 10-4 M carbamylcholine, and 10-4 M atropine, agonist and antagonist of the muscarinic Ach receptors, respectively, as well as with 10-7 M nicotine and 10-7 M D-tubocurarine chloride, agonist and antagonist of the nicotinic receptors, respectively. After exposure to these cholinergic drugs, cell pairing was perturbed. The cell surface pattern of wheat germ agglutinine-affinity sites, which were proved to be involved in pair formation, was enhanced in cells exposed to AchCl and was depressed in atropine-treated cells. From these outcomes, a complete set of cholinergic-like molecules is shown, including both receptor classes, whose activation or inhibition somehow interferes in Paramecium mating pair formation. J. Exp. Zool. 279:633–638, 1997. © 1997 Wiley- Liss, Inc.