The temperature dependence of cumulative spike plots. (A) Spikes were counted from traces such as those displayed in Fig. 2. Traces from 27 or more cells at each temperature were combined and normalized to the number of recordings. In each plot a point at a given time is the total number of spikes (>2 pA), seen up to that time point, per recording. The bar below the plot indicates the 6 s during which the cells were depolarized by pressure application of a high KCl solution. (B) The initial slope in the first 2 s was measured for each temperature. The logarithms of these slopes were then plotted versus one over the absolute temperature to give an Arrhenius plot. The activation energy, E_a, was obtained from the slope of this plot. (C) The sustained slopes of the cumulative spike plots in A were taken as the slope of the segment between 2 and 7 s. An Arrhenius plot was constructed as in B.