Fig. 3. A direct estimate of p and its comparison to p_train and p_EQ.

A. Plot of the relationship between initial release probability (p) and decay constant λ for a single pool of vesicles according to the equation p=1−e^(−1/λ). B. Plot of EPSC amplitudes simulated for a hypothetical synapse with one pool of vesicles with a single release probability (light gray, black) or two (dark gray) pools of vesicles with different release probabilities which each comprise 50% of the total RRP. For light gray symbols and curve, p=0.03; for dark gray symbols and curve, p₁=0.3 and p₂=0.03; and for black symbols and curve, p=0.3. C. Plot of EPSC amplitudes versus stimulus number for 100 Hz stimulus train with single exponential curve fit. The decay constant λ is 2.02 stimuli and can be used to estimate the probability of release. D. Plot of PPR vs p_train for experiments performed in varying Ca_e and in pharmacological manipulations of calcium entry (n=121). Dotted line corresponds to 1−p. E. A factor, f, was used to account for facilitation between the first and second action potentials. p_decay = p_decay(ss)/f. F. Plot of the facilitation factor, f, versus PPR for experiments performed in varying Ca_e and in pharmacological blockers to manipulate calcium entry (n=121). G. Plot of p_decay (open circles) and the uncorrected p_decay(ss) (black circles) versus p_EQ. Dashed line indicates the unity line, n=122. H. Plot of p_decay (open circles) and the uncorrected p_decay(ss) (black circles) versus p_train. Dashed line is the unity line. I. Plot of p_decay (open circles) and the uncorrected p_decay(ss) (black circles) normalized to p_train versus p_train. Dashed line is the unity line, n=122. J. Plot of p_decay (open circles) and the uncorrected p_decay(ss) (black circles) normalized to p_EQ as a function of p_EQ. Dashed line is the unity line, n=107.