Effects of nicotinic and muscarinic ligands on embryonic neurones of Periplaneta americana in primary culture: a whole cell clamp study.
The pharmacological properties of acetylcholine (ACh) receptors of cultured neurones from embryonic cockroach brains were studied using the whole-cell configuration of the patch-clamp technique. More than 90% of the studied neurones responded to ACh by a monophasic inward current, the intensity of which varied from cell to cell. The sequence of potency 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: high-affinity receptors (extrapolated K(d) around 10(-7) M) and low-affinity receptors (extrapolated K(d) around 5x10(-5) M). The current-voltage relationship of the induced current was linear between -80 and -40 mV and the extrapolated reversal potential was not significantly different from 0 mV. The sequence of decreasing potency of the antagonists of the ACh response was: methyllycaconitine > alpha-bungarotoxin > mecamylamine > curare > strychnine > bicuculline > atropine > picrotoxin. These results show: (1) that, in embryonic brain neurones, the response to ACh corresponds to the opening of non-selective cationic channels; and (2) that the pharmacology of the ACh receptors is mainly but not solely nicotinic. The nature of the single events which underlie this response, as well as the structure of the channels (homo or hetero-oligomeric) remain to be investigated.
Pichon
Y
Y
Groupe de neurobiologie, Equipe C.R.M., UPRES-A CNRS 6026, Université de Rennes, Campus de Beaulieu, F-35042, Rennes, France
Guillet
J C.
JC
Le Guen
J
J
Tiaho
F
F
Van Eyseren
I
I