Figure 5.

The pharmacological sensitivity, calcium dependence, and dependence on Na⁺-activated potassium channels of spike frequency adaptation and the subsequent afterhyperpolarization for single cells. A, The steady-state/peak firing rates (ss/peak) in DCN cells after delivering 200 pA depolarizing currents for 30 s in the indicated conditions. The effects of apamin (300 nm; a blocker of SK Ca²⁺-activated K channels), XE991 [10 µm; an antagonist of Kv7 channels (KCNQ, M-current)], and E4031 [a blocker of KCNH2 (ERG K channels)] were assessed. Low Ca solution consisted of 0.1 mm external Ca²⁺ and 4 mm external Mg²⁺; 0 Ca²⁺ solution consisted of 0 Ca²⁺ and 1 mm EGTA. Control, n = 18 cells (9 animals); apamin, n = 7 cells (4 animals); XE991, n = 5 cells (3 animals); E4031, n = 3 cells (2 animals); low Ca, n = 10 cells (7 animals); 0 Ca + EGTA, n = 7 cells (6 animals); Slo2.1/2.2 DKO, n = 9 cells (5 animals). The ss/peak for each experimental condition was not statistically significant from that of the control, as assessed by two-tailed unpaired Student's t tests. The threshold for statistical significance was set at p < 0.05. B, Peak firing rates observed during the depolarizing current step. Conditions with statistically significant differences from control are indicated with an asterisk (low Ca, p = 0.002; 0 Ca + EGTA, p = 0.004; two-tailed unpaired Student's t tests). All other comparisons with control were not statistically significant. C, Steady-state firing rates observed during the depolarizing current step. Conditions with statistically significant differences from control are indicated with an asterisk (low Ca, p = 0.014; 0 Ca + EGTA, p = 0.00079; nonparametric Wilcoxon signed-rank test). D, Decay times for the instantaneous firing frequencies occurring during the current step. Decay time for each experimental condition was not statistically significant compare with control, as assessed by two-tailed unpaired Student's t tests. E, Amplitude of the AHP observed in DCN neurons after the cessation of the depolarizing current step. Conditions with statistically significant differences from control are indicated with an asterisk (low Ca, p = 0.049; 0 Ca + EGTA, p = 0.015; two-tailed unpaired Student's t tests). All other comparisons with control were not statistically significant. F, The half-decay times for AHPs observed after each current step. Conditions with statistically significant differences from control are indicated with an asterisk (Slo2.1/2.2 DKO, p = 0.017; two-tailed unpaired Student's t tests test). All other comparisons with control were not statistically significant.