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Journal of Experimental Biology 131,231-244 (1987)
Published by Company of Biologists 1987

Gamma-Aminobutyric Acid Receptors on Cultured Cockroach Brain Neurones

T. SHIMAHARA 1, Y. PICHON 1, G. LEES 1, C. A. BEADLE 1, and D. J. BEADLE 1

1 Laboratoire de Neurobiologie Cellulaire et Moleculaire CNRS, 91190 Gif-sur-Yvette, France School of Biological Sciences and Environmental Health, Thames Polytechnic London SE18 6PF, UK

Gamma-aminobutyric acid (GABA) at 10-1 moll-1 inhibited spontaneous activity and produced conductance changes in 60% of cultured cockroach neurones tested. The reversal potential for the GABA-evoked response was between -65 mV and -75 mV. Under whole-cell voltage-clamp conditions, with 114mmoll-1 potassium chloride in the electrode, the reversal potential had a similar value to that predicted for a chloride current. The response was blocked by 10-5 moll-1 picrotoxin but was not affected by 10-5 moll-1 bicuculline. In the whole-cell voltage-clamp conditions, 50 µmoll-1 GABA evoked an inward current that was accompanied by an increase in current noise. Fluctuation analysis of the noise gave a mean channel opening time of 11.8 ms for GABA and 6.5 ms for muscimol. The single-channel conductance was 18.6 pS for GABA and 15.2 pS for muscimol. When 50 µmoll-1 GABA was applied in the presence of the benzodiazepine, flunitrazepam, there was an increase in both the evoked current and the accompanying current noise. Analysis of this noise gave values of 14.3 ms for the mean channel opening time and 18.3 pS for the singlechannel conductance. The variance of the noise was increased by approximately 60% in the presence of flunitrazepam, suggesting that this drug potentiates the GABA responses of cockroach neurones by increasing the frequency of channel events.

Note:

Present address: Pesticide Research Department, Wellcome Research Laboratories, Berkhamsted, Herts, UK.

Present address: Department of Biology, Oxford Polytechnic, Gipsy Lane, Headington, Oxford.

Key words: cultured insect neurones, GABA receptors, noise analysis, flunitrazepam

Accepted on April 30, 1987






© The Company of Biologists Ltd 1987