Effect of CaM-KII on the desensitization of GluR1. (A and B) Whole-cell (A) and outside-out patch (B) currents elicited by 10 mM glutamate at −80 mV in cells expressing GluR1 alone (Left) or the Ser-831-to-Glu mutant (Right). The currents were fitted by the sum of two exponentials for the rise and decay shown by the thin line. (C) τdes as a function of glutamate concentration for the whole-cell currents (n = 4). (D) τdes for whole-cell (open bars) and outside-out (gray bars) currents for GluR1 expressed alone, for GluR1 coexpressed with CaM-KII, for GluR1 with HI CaM-KII in the patch pipette, and for Ser-831-to-Glu and Ser-831-to-Asp mutants. (E) Time course of recovery from desensitization measured as the amplitude ratio of the second current to the first in pairs of glutamate applications. Points were fitted by exponential (solid line) with the time constant τrec. (Insert) Currents elicited by paired applications of 10 mM glutamate (20-ms pulses) with time intervals 10–1,000 ms after the end of the first application. (F) τrec for cells with GluR1 alone, for cells with GluR1 and CaM-KII, and for Ser-831-to-Glu and Ser-831-to-Asp mutants.