Junctional and extrajunctional membrane channels activated by GABA in locust muscle fibres

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Abstract
Iontophoretic application of GABA to voltage-clamped locust [Schistocerca gregaria] muscle fibers demonstrated the presence of both extrajunctional and junctional GABA receptors. Extrajunctional GABA receptors were distinct from extrajunctional glutamate receptors which occurred in these muscle fibers. Inward GABA currents were nonlinearly dependent on membrane potential. Analysis of membrane current noise produced by iontophoretic GABA application showed that for junctional and extrajunctional GABA receptors the mean channel lifetime was 3-4 ms and the single-channel conductance was .apprx. 22 pS at -80 mV (T = 21.degree. C). Mean life time of the inhibitory channel decreased with membrane hyperpolarization as previously demonstrated for glutamate-sensitive excitatory channels in locust muscle fibers.