Nicotinic receptors in Lymnaea stagnalis neurons are blocked by alpha-neurotoxins from cobra venoms

The influence of cobra neurotoxins on the Cl-dependent responses to acetylc holine (ACh) of Lymnaea neurons was studied by the voltage-clamp technique. It was found that a short chain neurotoxin II (NT II), a long chain cobrat oxin (CTX) and weak neurotoxin (WTX) diminished the ACh-induced currents, t he block being concentration-dependent and competitive. The IC50 values of 130 nM for CTX, 11 muM for NT 11, and 67 muM for WTX were determined. The b lock induced by NT II was quickly reversible upon toxin washout, whereas th e action of CTX and WTX was only partially reversible even after an hour of intensive washing. The data obtained suggest that acetylcholine receptors (AChRs) in Lymnaea neurons have common features with cation-selective alpha 7 AChRs of vertebrates and one type of Aplysia CI-conducting AChRs. (C) 200 1 Elsevier Science Ireland Ltd. All rights reserved.