Figure 5. Effect of [Ca²⁺]_i buffering on depolarization-induced inhibition of EPSCs.

All records were obtained in Mg²⁺-free Ringer solution. A, light-evoked EPSCs were recorded before and 100 ms after a 400 ms depolarizing step from -70 to 0 mV, either within 1 min of membrane rupture or after 10 min incubation with BAPTA (10 mm in the patch pipette). The presentation, but not the timing, of the depolarizing pre-pulse is represented above the traces. Dotted lines indicate the peak current observed before the depolarizing step. B, histogram of these results (n = 4, P < 0.01). C, with 10 mm caffeine in the patch pipette, the inhibitory effect of depolarization on EPSCs was recorded within 1 min of patch break and 10 min later. Caffeine by itself reduced EPSCs by 36 ± 5 % (n = 7, P < 0.01, compare first and third traces) and abolished the inhibitory effect of depolarization. D, histogram summarizing the inhibitory effect of depolarization on EPSC amplitude within 1 min of patch break, and after 10 min exposure either to caffeine (Caff, n = 5, P < 0.005) or to IP₃ (50 μm, n = 4, P < 0.002).