Figure 2.
Effect of SNPs on Cav3.2 steady-state inactivation and persistent currents. A, Representative current traces obtained during a test pulse to -35 mV after 1 s prepulses to varying potentials. Voltage protocol is shown above the traces. The cell was held at -115 mV for 10 s between sweeps. After the last depolarizing prepulse (-55 mV), the cell was tested again with a -125 mV prepulse. Typically, 95% of the original current was recovered, thereby excluding the effect of rundown. B, Inactivation (h∞) was calculated as the fraction of current available after each prepulse (I) divided by the current recorded after the first prepulse to -125 mV (Imax). Data from each cell were fit with a Boltzmann equation, and the resulting values of V50 and k were averaged (number of cells and values reported in Table 2). Smooth curves represent the average fits. Dotted line represents the activation curve for WT channels as described in Figure 1. The activation and inactivation curves overlap at approximately -70 mV. C, The percentage of channels in the overlap region was calculated as the product of the Boltzmann functions describing each process. D, Representative current traces obtained at the end of 150 ms depolarizing pulses to -55 mV. The downward spike represents the tail current triggered by repolarization. Dotted line represents the zero current baseline. E, The residual current at 150 ms (I150) was divided by the maximal current observed in that cell (Imax), averaged, and then plotted as a function of test potential. Data represent mean ± SEM, in which the number of cells used to calculate the average is reported in Table 3. Only data that were significantly different from WT is plotted.