Figure 1.

A, spontaneous firing of neurons expressing either wild-type (WT) (Aa) or C456S (Ab) channels recorded in the whole-cell current-clamp mode. To measure spontaneous firing without cell dialysis, we used the loose cell-attached patch recording mode. B, representative traces of spontaneous activity measured from neurons transfected with either WT (Ba) or C456S (Bb). Scale bars are shown at the ends of traces Aa and Ba. C, average spontaneous firing recorded in loose cell-attached patch configuration (n = 15 or 16). The Mann–Whitney test was used for statistical analysis. ***Significance at P < 0.001. A non-conducting mutant, D1504K, was used as a transfection control (n = 6). D, the time interval between action potentials (APs) was calculated and expressed as the cumulative probability. The grey shaded area corresponds to APs that were separated by <100 ms. E, the selective T-type Ca²⁺ channel blocker TTA-P2 (1 μm) blocked spontaneous firing by 66% (C456S 1.2 ± 0.4 Hz, TTA-P2 0.4 ± 0.2 Hz; n = 6, P < 0.05) and significantly increased the median inter-spike interval from 5 ms to 29 ms (95% confidence intervals: C456S, 3–8; plus TTA-P2, 27–31).