FIGURE 4. Kiss-and-run, compensatory and stranded events.

a, F histogram calculated without stimulation in standard calcium concentration characterizes baseline variability and is normally distributed ( = 3.3; P = 0.47, ² test, d.f. = 8). b, Using the same traces as in a, a F histogram computed for one action potential in standard calcium has a peak at +q, the quantal size in high calcium concentration (see Fig. 3c) (P = 0.99, ² test, d.f. = 16). The histogram is clipped at - ( = 3.3) for clarity. c, The average of 72 traces with F values within +q (11 3.4) in grey. The fit (in black) has three decay components: (1) fast, kiss-and-run monoexponential process ( = 860 210 ms); (2) slow, compensatory gaussian process ( = 10.7 0.35 s); and (3) stranded > 45 s. The standard deviation of the compensatory fitted component constrained by the coefficient of variation found for events in high calcium (see Fig. 3d; / = 4.2). d, Individual examples of compensatory and stranded recycling events (in grey). e, Three individual traces of kiss-and-run recycling with an average of 24 in grey; an 860-ms decay is overlaid in black. f, The relative frequencies of three kinds of release events, failures and evoked retrievals, in standard calcium concentration.