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 acetylcholine (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 cobratoxin (CTX) and weak neurotoxin (WTX) diminished the ACh-induced currents, the block being concentration-dependent and competitive. The IC(50) values of 130 nM for CTX, 11 microM for NT II, and 67 microM for WTX were determined. The block induced by NT II was quickly reversible upon toxin washout, whereas the 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 Cl-conducting AChRs.