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The action of GABA receptor agonists and antagonists on muscle membrane conductance in Schistocerca gregaria
Author(s) -
Murphy V.F.,
Wann K.T.
Publication year - 1988
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1988.tb11697.x
Subject(s) - picrotoxin , bicuculline , muscimol , gabaa receptor , chemistry , biophysics , nipecotic acid , gaba receptor antagonist , pharmacology , receptor , biology , biochemistry , neurotransmitter
1 The properties of postsynaptic γ‐aminobutyric acid (GABA) receptors in the extensor tibiae muscle of Schistocerca gregaria were studied by conventional electrophysiological recording techniques. 2 GABA and other active GABA receptor agonists produced rapid, dose‐dependent, reversible increases in membrane conductance. 3 In two microelectrode experiments the ED 50 for GABA was approximately 1 mM. In three microelectrode experiments (assuming short cable theory conditions) the ED 50 for GABA was 2.3 mM. The Hill coefficient for GABA estimated from the latter experiments was 1.4 4 The relative potency of muscimol/GABA at the ED 50 for GABA was 1.36. 3‐Aminopropane sulphonic acid (3‐APS) and isonipecotic acid were weakly active, baclofen and piperidine‐4‐sulphonic acid (P4S) were inactive. Isoguvacine produced depolarizations and increases in conductance in preparations which hyperpolarized in response to GABA. These depolarizations were enhanced by both picrotoxin and pitrazepin although the increases in input conductance were depressed. 5 Picrotoxin (20 μ m ), (+)‐bicuculline (20–100 μ m ) and pitrazepin (1–10 μ m ) all reversibly antagonized GABA‐induced responses. Such antagonism was not competitive in the case of picrotoxin and (+)‐bicuculline but was competitive for pitrazepin. Schild plot analysis gave an average pA 2 value of 5.5 for pitrazepin. 6 The significance of these results is briefly discussed.