Figure 2. Optimized parameter sets showing the changes in activation kinetics of presynaptic Ca²⁺ channels in model I.

A total of 256 randomly-seeded parameter sets were optimized for model I to fit the experimental recording of the synaptic outputs in control and proctolin for two different presynaptic voltage amplitudes (see Methods). (a) The distribution of parameter values for each of the 16 parameters in model I is indicated in grayscale, with darker tones representing greater distribution density. The value of each parameter was normalized to the mean value of its distribution (dashed blue line) for comparison; these mean values are: K_Ca = 1.3μM, ḡ_syn = 14.1nS / μM⁴, ḡ_Ca = 1.8nS, g_m = 0.46μS, τ_h = 1.6s, τ_Ca = 33.6ms, ${\tau }_m^c=39.7ms$, V_h = 78.5mV, S_h = 41mV, V_m = 42mV, S_m = 8.7mV, $V_m^p=50\mathit{\text{mV}},S_m^p=2.8\mathit{\text{mV}},A_{\tau }^p=2.0s,V_{\tau }^p=50.5\mathit{\text{mV}},S_{\tau }^p=5.9\mathit{\text{mV}}$ Two parameter sets are also shown for comparison (red and yellow), demonstrating that good fits to the data did not require a consistent relationship among all parameters. Six out of 16 parameters were relatively tightly constrained by the optimization technique (coefficient of variation < 0.4 shown in blue). (b) Pair-wise correlations among the best-fit parameters indicate that few parameter pairs showed any significant (R > 0.5) co-variation. See Results for additional description.