Fig. 7.
Equilibrium binding and steady-state desensitization. A, Equilibrium binding of [3H]GABA. Oocytes were incubated for 30 min with the indicated concentrations of [3H]GABA. Thefilled symbols represent the average of three oocytes. The continuous line is a fit of the Hill equation of these data yielding a apparent KD of 0.040 μm and a Hill coefficient of 1.22. B, Determination of the steady-state level of desensitization. An oocyte was voltage clamped at −70 mV, and the indicated concentrations of GABA were applied successively. All four concentrations of GABA were saturating in terms of desensitization. The amplitude of the baseline current at the end of the application was used to calculate the maximum fraction of receptors in the desensitized state, which was 0.049 of the peak GABA-activated current.