EFFECTS OF NICOTINIC AND MUSCARINIC LIGANDS ON EMBRYONIC NEURONS OF PERIPLANETA-AMERICANA IN PRIMARY CULTURE - A WHOLE-CELL CLAMP STUDY

The pharmacological properties of acetylcholine (ACh) receptors of cul tured neurones from embryonic cockroach brains were studied using the whole-cell configuration of the patch-clamp technique. More than 90% o f the studied neurones responded to ACh by a monophasic inward current , the intensity of which varied from cell to cell. The sequence of pot ency of the five tested agonists was ACh > nicotine = carbamylcholine > suberyldicholine = oxotremorine. The dose-response relationship was complex, suggesting the existence of two populations of receptors: hig h-affinity receptors (extrapolated K-d around 10(-7) M) and low-affini ty receptors (extrapolated K-d around 5 x 10(-5) M). The current-volta ge relationship of the induced current was linear between - 80 and - 4 0 mV and the extrapolated reversal potential was not significantly dif ferent from 0 mV. The sequence of decreasing potency of the antagonist s of the ACh response was: methyllycaconitine > alpha-bungarotoxin > m ecamylamine > curare > strychnine > bicuculline > atropine > picrotoxi n. These results show: (1) that, in embryonic brain neurones, the resp onse to ACh corresponds to the opening of non-selective cationic chann els; and (2) that the pharmacology of the ACh receptors is mainly but not solely nicotinic. The nature of the single events which underlie t his response, as well as the structure of the channels (homo or hetero -oligomeric) remain to be investigated. (C) 1998 Elsevier Science Ltd. All rights reserved.