Figure 5.

High-voltage-activated, ryanodine-insensitive release is susceptible to depression. A, In dual recordings of a rod and a synaptically connected OFF bipolar cell, EPSCs were recorded in the OFF bipolar cell clamped at −70 mV while the rod was stimulated with paired pulses (−80 to −20 mV; 100 ms stimuli separated by 2 s). The early phase of the EPSCs exhibited paired-pulse depression, and the late phase recovered fully (dark trace). Ryanodine at 100 μm suppressed only the late, sustained component (gray trace) and did not alter the paired-pulse depression. Calcium buffering in the rod was reduced by using 1 mm EGTA in the recording pipette. B, A similar dual-cell recording was performed but using 5 mm BAPTA in the rod recording pipette. An EPSC was recorded from an OFF bipolar cell voltage clamped at −70 mV while the connected presynaptic rod was stimulated with a step from −80 to −20 mV for 100 ms (gray trace). The trace is overlaid with the control trace from A for comparison. Buffering of the rod with 5 mm BAPTA results in suppression of the sustained component. C, Recording of calcium currents in a rod depolarized by paired pulses (−80 to −30 mV for 40 ms, with an interpulse interval of 60 ms).