Figure 5. Variance-mean analysis of paired-pulse responses.

A, paired AMPA EPSCs were evoked under a range of release probability conditions following bath application of cadmium (a, Cd; 8 μM), physiological calcium (b, Ca; 2 mM) and elevated calcium (c, Hi Ca; 6 mM) (inset). Variance-mean analysis was applied to both the first (•) and the second EPSCs (^). The variance-mean relationship of the first response followed a simple parabola while the variance-mean relationship of the second response was unexpectedly non-parabolic, curling back on itself when P_r was elevated in high calcium (c′). B, in most neurons, the second EPSC did not deviate from the first EPSC under conditions of low to normal (Ca; 2 mM) P_r, as shown for this individual neuron.