Competitive interaction of beta-guanidino propionic acid and gamma-aminobutyric acid on the muscle fibre of the crayfish.

1. The interaction of beta-guanidino propionic acid and gamma-aminobutyric acid has been investigated on the crayfish muscle by measurement of the membrane conductance.2. The increase in membrane conductance produced by GABA is depressed by beta-guanidino propionic acid. This antagonist acts in a competitive way as shown by the shift of log dose-response curves and by the results of tests for competitive interaction (method of Schild (1947); Lineweaver and Burk's plot).3. Perfusion of GABA was shown to induce a receptor desensitization. As a consequence, the slope of the dose-response curve plotted in Hill's co-ordinates increases when care is taken to minimize this phenomenon. The significance of this slope for establishing the real number of GABA molecules binding with the GABA receptor is discussed.