Figure 5.

Manganese increases firing rate in the combined absence of extracellular and intracellular Ca². A, Top, Representative trace of spontaneous spike activity following Mn²⁺ exposure in a Ca²⁺-free extracellular solution and an intracellular solution containing the Ca²⁺ chelator BAPTA (10 mm). Bottom, Histogram of firing frequency obtained from above trace showing Mn²⁺ increased firing frequency. B, Superimposed representative single AP traces are shown in A: baseline (black trace), 100 μm Mn²⁺ + Ca²⁺-free + BAPTA (red trace) and Ca²⁺-free + BAPTA-AM (green trace). C, Mn²⁺ increased firing rate, even in the combined absence of extracellular and intracellular Ca²⁺; after Mn²⁺ washout, the firing rate decreased under Ca²⁺-free conditions (baseline: 0.9 ± 0.2 Hz vs 100 μm manganese: 6.9 ± 1.7 Hz, F_(2,26) = 13.2, p = 0.003, one-way ANOVA followed by Tukey's test; n = 10/group). D, The combination of extracellular Ca²⁺-free + Mn²⁺ and intracellular BAPTA-containing solution depolarized the membrane potential. After Mn²⁺ washout, the membrane potential returned to the baseline level (Ca²⁺-free conditions) (baseline: −54.9 ± 1.3 mV vs 100 μm manganese: −49.6 ± 1.9 mV; F_(2,27) = 2.5, p = 0.028, one-way ANOVA followed by Tukey's test; n = 9/group). E, The half-width was measured at the half-maximal voltage of APs. The half-width was broadened significantly in the combination of extracellular Ca²⁺-free + intracellular BAPTA-containing solution in the absence or presence of Mn²⁺ (baseline: 1.37 ± 0.2 ms vs 100 μm manganese: 2.50 ± 0.3 ms; F_(2,24) = 3.5, p = 0.009, one-way ANOVA followed by Tukey's test; n = 10/group). F, Half-amplitude of AP was significantly depressed in extracellular Ca²⁺-free solution combined with intracellular BAPTA in the absence or presence of Mn²⁺ (baseline: 37.5 ± 1.4 mV vs 100 μm manganese: 29.0 ± 1.7 mV; F_(2,24) = 6.0, p = 0.001, one-way ANOVA followed by Tukey's test; n = 9/group). G, The CVs of the interspike intervals were not significantly different among the experimental groups. *p < 0.05, **p < 0.01. n = 9 or 10 per group.