title: Synthesis of the signal molecule acetylcholine during the developmental cycle of Paramecium primaurelia (Protista, Ciliophora) and its possible function in conjugation.
abstract: We recently discovered, in mating-competent Paramecium primaurelia, the presence of functionally related molecules of the cholinergic system: the neurotransmitter acetylcholine (ACh), both its nicotinic and muscarinic receptors and its lytic enzyme acetylcholinesterase (AChE). Our results on the inhibition of mating-cell pairing in vivo in mating-competent cells treated with cholinomimetic drugs support the hypothesis that the cholinergic system plays a role in cell-to-cell adhesion. To investigate the possible function of the signal molecule ACh in conjugation in P. primaurelia, we attempted to detect the intracellular sites of ACh synthesis by localizing the ACh biosynthetic enzyme choline acetyltransferase (ChAT). Using immunocytochemical and histochemical methods, we have demonstrated the presence and activity of ChAT principally on the surface membrane of mating-competent cells and of mature but non-mating-competent cells. No evidence for ChAT activity was found in immature cells. Immunoblot analysis revealed the presence of immunoreactive bands, ranging in molecular mass from 42 to 133 kDa, as reported for ChAT isolated from higher organisms. In vivo experiments showed that inhibition of ChAT activity by Congo Red, known to be a potent competitive inhibitor of acetyl coenzyme A, did not affect mating-cell pairing. Conversely, inhibition of AChE with BW 284c51 or eserine, which block enzyme activity by reacting with a specific serine within the catalytic centre, significantly inhibited mating-cell pairing. Our results suggest that ACh has a negative modulating effect on conjugation in P. primaurelia.
authors: Department for the Study of the Territory and its Resources, University of Genoa, Corso Europa 26, I-16132 Genoa, Italy. corrado@dipteris.unige.it
authors: M U
authors: MU
authors: Delmonte Corrado
authors: H
authors: H
authors: Politi
authors: M
authors: M
authors: Ognibene
authors: C
authors: C
authors: Angelini
authors: F
authors: F
authors: Trielli
authors: P
authors: P
authors: Ballarini
authors: C
authors: C
authors: Falugi
mesh_terms: D000109:Acetylcholine / Q000096:biosynthesis*; D000110:Acetylcholinesterase / Q000378:metabolism; D000818:Animals; D002448:Cell Adhesion; D002795:Choline O-Acetyltransferase / Q000378:metabolism; D002800:Cholinesterase Inhibitors / Q000494:pharmacology; D007150:Immunohistochemistry; D010247:Paramecium / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism*; D010830:Physostigmine / Q000494:pharmacology; D012098:Reproduction / Q000502:physiology; D015398:Signal Transduction
chemical_list: D002800:Cholinesterase Inhibitors; D010830:Physostigmine; D002795:Choline O-Acetyltransferase; D000110:Acetylcholinesterase; D000109:Acetylcholine