Minimal model to account for the membrane conductance increase and desensitization of .gamma.-aminobutyric acid receptors synthesized in the Xenopus oocytes injected with rat brain mRNA

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Abstract
.gamma.-Aminobutyric acid (GABA) receptors, which translocate chloride anion with binding GABA, were synthesized in Xenopus oocytes by injecting rat brain mRNA. GABA-elicited responses in the oocytes were measured electrophysiologically by the current-clamped method. Five different measurements were made to establish the relationship between GABA concentration and the electrical responses: (1) the GABA-elicited conductance increase before desensitization; (2) the rate of desensitization of GABA receptors; (3) the rate of recovery of desensitized receptors upon removal of GABA; (4) the GABA-elicited conductance increase after desensitization equilibrium; (5) the fraction of the active form of GABA receptors after desensitization equilibrium. These results were interpreted on the basis of the minimal model proposed for nicotinic acetylcholine receptor in Electrophorus electricus electroplax [Hess, G. P., Cash, D. J., and Aoshima, H. (1983) Annu. Rev. Biophys. Bioeng. 12, 443-473]. Estimated equilibrium and rate constants in the model for GABA receptors could successfully explain the results of the five above measurements.