Figure 2.
Similar kinetics and Ca2+ dependence of exocytosis in calyceal terminals of wt and CaV1.3−/− mice. A, Presynaptic ICa(V) recorded during depolarizations of 5, 17, and 33 ms duration from Vh = −80 mV to 0 mV (left) and corresponding changes in membrane capacitance (Cm, top traces), membrane resistance (Rm, middle traces), and series resistance (Rs, bottom traces) (right). ΔCm was estimated from averaged Cm values measured during a 50 ms time window ≥190 ms after the end of depolarizations. B, Average ICa(V) (B2) and corresponding average ΔCm values (B1) plotted against Vm for step depolarizations of 10 ms duration obtained from wt (black) and CaV1.3−/− (red) mice. Note the similar voltage dependence of ICa(V) and ΔCm. C, Average ΔCm values plotted against measured Ca2+ charge (QCa) during presynaptic depolarizations of variable duration (1, 2, 3, 5, 9, 17, and 33 ms). Pooled data from wt (black) and CaV1.3−/− (red) calyces (P14–P17). Dotted lines represent extrapolations using the first ΔCm/QCa ratio obtained with an AP-like depolarization (1 ms, 0 mV). For longer stimuli, ΔCm/QCa decreases, presumably because of vesicle depletion.