The purpose of this project is to analyze the molecular events which result in a change in ion permeability of the postsynaptic excitable membrane in response to neurotransmitter substances during synaptic transmission. The system studied is in the inhibitory neuromuscular junction in arthropods and inhibitory synapses in mammalian central nervous systems where the neurotransmitter compound is gamma-aminobutyric acid (GABA). The approach is to define, isolate, and study the membrane proteins involved in the phenomena: the receptor and ionophore proteins. The activity of these proteins is defined in vitro by radioactive ligand binding assays; the binding must be consistent with in vivo properties of the system. Chemical studies on GABA agonist and antagonist compounds, such as GABA analogs and the drugs picrotoxin and bicuculline, as well as a search for a specific GABA-blocking toxin are part of this approach. Insights into the mode of action of several drugs (molecular pharmacology) will likely be obtained. Fractionation of tissue containing GABA receptors will allow enrichment of excitable membranes, which will be assayed in vitro for GABA regulation of ion permeability. With an unambiguous assay for the GABA receptor and perhaps ionophore, these proteins will be localized to a cellular fraction, solubilized by mild detergents, their physical properties studied, and purified by affinity chromatography. The purified proteins will then be reconstituted into membranes for analysis of their molecular roles in the regulation of excitable membrane ion permeability by neurotransmitter substances. It is hoped that the complex cellular events of the synapse can be reduced to a biochemistry project. The information gained will relate to biomedical problems of nerve and muscle tissues. BIBLIOGRAPHIC REFERENCES: Olsen, R. W., Approaches to Study of GABA Receptors, in, GABA IN NERVOUS SYSTEM FUNCTION (Eds.) E. Roberts, T. N. Chase and D. Tower, Raven Press, New York (1976) pp. 287-304. Olsen, R. W., M. Ban and T. Miller, Studies on the Neuropharmacological Activity of Bicuculline and Related Compounds Brain Res. 102, 283-299 (1976).