Figure 5.

Unaltered calyceal AP waveform but higher sensitivity of SV exocytosis to intracellular EGTA in P16–P21 Cplx1^−/− calyx terminals. A, Representative presynaptic calyceal APs elicited by afferent fiber stimulation and recorded in current-clamp configuration in a P17 Cplx1^+/+ (black) and a P18 Cplx1^−/− (red) terminal. B, Average AP amplitudes (left) and AP half-widths (right) were similar in Cplx1^+/+ (black) and Cplx1^−/− (red) terminals. Number of terminals tested as indicated. C, AP waveform is stable during repetitive presynaptic high-frequency firing. AP trains consisting of 35 APs elicited at a frequency of 100 Hz in a Cplx1^+/+ (black) and a Cplx1^−/− (red) terminal. Left, The first three and last three APs in the trains. Right, The first and last AP are shown superimposed for comparison. D–F, Presynaptic Ca²⁺ influx (D1, E1, F1) and SV exocytosis (D2, E2, F2) in response to AP-like depolarizations (1 ms steps to 0 mV). D, Representative recordings from a Cplx1^+/+ (black) and a Cplx1^−/− (red) terminal with 5 mm EGTA in the pipette solution. Note the similar I_Ca(V) but strongly attenuated ΔC_m in the Cplx1^−/− calyx terminal. E,F, Average traces for I_Ca(V) and ΔC_m recorded in Cplx1^+/+ (E) and Cplx1^−/− (F) terminals with either 0.5 mm EGTA (black traces) or 5 mm EGTA (red traces) in the pipette solution. Light gray and light red areas in (E2, F2) represent ±SEM. Although exocytosis in Cplx1^+/+ terminals was relatively insensitive to the slow Ca²⁺ chelator EGTA (E), the latter attenuated the average ΔC_m value by ∼50% in Cplx1^−/− terminals (F).