Fig. 1.

GluR1 and GluR4 channels desensitize at glutamate concentrations that produce minimal activation. a,d, Currents evoked by 5 mm glutamate in control solution and after equilibrating patches containing GluR1 (a) and GluR4 (d) channels with the indicated concentrations of glutamate. b,e, Steady-state plateau currents evoked in cells expressing GluR1 (b) and GluR4 (e) channels by the indicated applications of glutamate (bars). c, f, Concentration–response curves for glutamate-induced desensitization (squares), the steady-state plateau current (triangles), and the peak current (circles; from results like those shown in Fig.3b,c) for GluR1 (c) and GluR4 (f) channels. Eachsymbol is the mean value obtained from measurements in four to nine patches or cells. Results from individual patches or cells were normalized to the amplitude of the peak current evoked by 5 mm glutamate in the absence of preincubation (glutamate-induced desensitization), the plateau current evoked by 1 mm glutamate, and the peak current evoked by 50 mm glutamate. Error bars indicate SEM for each set of data. Some of the error bars in this and subsequent figures are less than one-half the symbol size.