Molecular Pharmacology, Vol 9, 580-589, Copyright © 1973 by the American Society for Pharmacology and Experimental Therapeutics

The Kinetics of the Conductance Increase Produced by -Aminobutyric Acid at the Membrane of Locust Muscle Fibers

¹ Department of Pharmacology, Hebrew University-Hadassah Medical School, Jerusalem, Israel
² Department of Physiology, College of Physicians and Surgeons, Columbia University, New York, New York 10032
³ Institute of Life Sciences, Hebrew University, Jerusalem, Israel

The membrane response to -aminobutyric acid (GABA) of locust muscle fibers bathed in "propionate saline" at pH 6.5 is generally biphasic. The slow phase is exponential, and its rate constant (5.5 x 10^-3 to 1.0 x 10^-2 sec^-1) is independent of GABA concentration and relatively insensitive to temperature change (from 26° to 15°). With increasing GABA concentration and temperature, a faster process intervenes. A form of "sensitization" occurs in which the participation of the fast component of the kinetics increases on repeated application of the same GABA concentration. Equilibrium curves of GABA action were obtained at different temperatures, and a van't Hoff plot was constructed. The standard enthalpy change, H°, for the over-all interaction between GABA and receptor is -59.3 kcal/mole.

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