Fig. 8.
Ca2+-induced changes in response kinetics contribute to inhibition of the response during hyperpolarization. A, Each trace is the average of four responses obtained in a bathing solution with 0 mm Ca2+ (thintrace) or 5 mm Ca2+(thicktrace). Ca2+depressed the steady-state cation current, but in this cell the depression was relieved briefly after the wash off of glutamate.Inset, The Ca2+-dependent decay of cation current was exponential, with a time constant of ∼0.8 sec in this cell. Calibration: 20 pA, 1 sec. B, I–Vrelations of the glutamate response using brief voltage steps as described in Figure 7 are shown. Steady-state responses were measured in 0 mm Ca2+(filledcircles;n = 10) or 5 mm Ca2+(opencircles; n = 9). The slope conductance for 0 mm Ca2+was 2.06 nS. In a third group of cells, the “peak” response was measured in cells that displayed a significant undershoot (opensquares; n = 11), by summing the size of the undershoot and the steady-state response. This group was obtained by pooling cells that were recorded with 5 mm Ca2+ (7 cells) and 2 mm Ca2+ (4 cells). The 0 mmCa2+ group includes only cells that displayed a significant undershoot with Ca2+ in the bathing medium.