Some Effects of Anticholinesterase Drugs and their Antidotes on Extraretinal Photoreceptor Cells of Aplysia Californica

摘要

Aplysia extraretinal photoreceptor (ERP) cells R sub 2, LPL sub 1, and VPN were used as models of phototransduction. The effects of clolinesterase inhibitors and their antidotes on photoresponses in Aplysia ERP cells were investigated by electrophysiological methods. Bath application of diisopropyl fluorophosphate (DFP), a potent irreversible organophosphate-type cholinesterase inhibitor, consistently decreased the maximum amplitude of the photoresponse elictied by flashing a light on Aplysia ERP cells. Physostigmine, a reversible carbamate-type cholinesterase inhibitor, depressed both photoresponse amplitude and membrane resistance. Both drugs caused depolarization of the resting membrane potential (RMP). Pyridostigmine, another reversible carbamate-type cholinesterase inhibitor, had no effect on photoresponse or membrane resistance at five times the concentration used for physostigmine. Bath application of carbachol, which would mimic a build up of acetylcholine (ACh) following cholinesterase inhibition, caused a persistent hyperpolarization of the RMP. Carbachol caused attenuation of both photoresponse and membrane resistance. Calcium-free sea water did not block DFP's effects. These results suggest that the effects of DFP on ERP cells are not due simply to a buildup of ACh at synapses subsequent to cholinesterase inhibition. Atropine's block of DFP's effects might be caused by competition for binding sites.