Fig. 1.

Intrinsic Ca²⁺ sensitivity of transmitter release. Shown is P_r for a single vesicle when exposed to a [Ca²⁺] transient with a time course equal to that of whole-cellI_Ca (full width at half-maximum, 383 μsec) and with a peak amplitude of [Ca²⁺]_vesicle. The thin lines indicate release probability during APs according to Release Model A (P_r, vesicle = 25% at [Ca²⁺]_vesicle = 8.8 μm; Bollmann et al., 2000) or Release Model B (P_r, vesicle = 10% at [Ca²⁺]_vesicle = 35 μm; Schneggenburger and Neher, 2000).