Cholinesterase activity and effects of its inhibition by neurotoxic drugs in Dictyostelium discoideum Carla Falugi a , Andrea Amaroli b , Valentina Evangelisti c , Aldo Viarengo c , Maria Umberta Delmonte Corrado b, * a Department of Experimental, Environmental, and Applied Biology, University of Genoa, Viale Benedetto XV 5, I-16132 Genoa, Italy b Department for the Study of the Territory and of its Resources, University of Genoa, Corso Europa 26, I-16132 Genoa, Italy c Department of Sciences and Advanced Technologies, University of East Piemonte ‘‘Amedeo Avogadro’’, Corso Borsalino 54, I-15100 Alessandria, Italy Received 5 July 2001; received in revised form 21 March 2002; accepted 21 March 2002 Abstract Recently, we found acetylcholinesterase (AChE) activity in the ciliate protozoan Paramecium primaurelia. Asinthe slime mould Dictyostelium discoideum the presence of a serine esterase was found with strong sequence identity to Torpedo AChE, we extended to D. discoideum the investigation on the characterization and possible functions of cholinesterases (ChEs). In amoeboid cells, histochemical, biochemical, and electrophoresis analyses evidenced both a ChE activity able to hydrolyze the substrate PrTChI, and AChE (E.C. 3.1.1.7.) activity similar to Electrophorus elec- tricus AChE. Conversely, butyrylcholinesterase activity was nearly absent, according to our previous results on P. primaurelia.Moreover,thepossibilitytoutilize D. discoideum inabioassayforthepre-chemicalscreeningbothofmoist environments and fresh waters, in relation to the occurrence of the neurotoxic organophosphate drugs, such as ‘‘basudin’’, inhibiting ChE activity, was investigated. Exposure to basudin inhibited propionylcholinesterase (PrChE) activityinadose-dependentmannerintherange10 1 –10 7 M(60%at10 4 M),withoutanysignificanteffectonAChE activity. PrChE activity was inhibited slightly by 10 5 Meserine,andreducedsignificantlybothby10 5 M iso-OMPA andBW284C51,classicallyusedtodiscriminatethedifferentChEmolecularforms.Theeffectsoncellmorphology,cell density, and differentiation were evaluated in cultures exposed to PrTChI 10 5 M or basudin 10 4 M for a three-day period. The PrTChI-exposed sample exhibited cell morphology, cell density, ability to aggregate, and to form fruiting bodiessimilartothecontrol;whereas,thebasudin-exposedsampleshowedanomaliesincellmorphologyandlowercell density than the control, together with inability to aggregate. Ó 2002 Published by Elsevier Science Ltd. Keywords: Acetylcholinesterase; Propionylcholinesterase; Organophosphate compounds; Slime moulds; Protista 1. Introduction The presence of molecules belonging to the cholin- ergicsignalingsystemwasrecentlydetectedintheciliate protozoan Paramecium primaurelia, including the signal molecule ACh, its biosynthetic and lytic enzymes, cho- line acetyltransferase and AChE, as well as both ACh nicotinic and muscarinic receptors. A possible role of these functionally related molecules was suggested in modulating cell interactions leading to cell-to-cell ad- hesionduringconjugation(Triellietal.,1997;Delmonte Corradoetal.,1999,2001).Inthelightofthesefindings, the investigation on the presence and possible functions of ChEs was extended to the slime mould Dictyostelium Chemosphere 48 (2002) 407–414 www.elsevier.com/locate/chemosphere * Corresponding author. Tel.: +39-010-3538031; fax: +39- 010-3538209. E-mail address: corrado@dipteris.unige.it (M.U. Delmonte Corrado). 0045-6535/02/$ - see front matter Ó 2002 Published by Elsevier Science Ltd. PII:S0045-6535(02)00143-1