Figure 3. Substitution of Li⁺ for Na⁺ markedly inhibits mitochondrial Ca²⁺ efflux in hippocampal neurons.

(A) and (B), Representative traces from experiments with simultaneous monitoring of [Ca²⁺]_cyt (Fura-2; black) and [Ca²⁺]_mt (mito-RGECO1; red) in cultured hippocampal neurons. [Ca²⁺]_cyt and [Ca²⁺]_mt transients were induced by brief depolarization using 30 mM KCl (K⁺30, 15 s, arrows). Substitution of Li⁺ for Na⁺ in the extracellular solution (0 mM Na⁺, 140 mM Li⁺) is indicated by blue bar under the traces. In (B), extracellular Ca²⁺ was removed (0 mM Ca²⁺, 100 µM EGTA) immediately after K⁺30 stimulation (purple bars). (C), Mitochondrial Ca²⁺ efflux kinetics was quantified by measuring the duration of 70% [Ca²⁺]_mt recovery relative to its peak elevation (T₇₀), and compared between the control conditions (140 mM NaCl in extracellular solution) and following Na⁺ replacement with Li⁺ in the extracellular solution. Data are presented as mean ± SEM, n=36; ****p<0.0001, two-tailed paired Student’s t-test. (D) Representative traces of [Ca²⁺]_cyt (black) and [Ca²⁺]_mt (red) show the effect of the mtNCX inhibitor CGP37157 (10 μM; green bar) on mitochondrial Ca²⁺ efflux in hippocampal neurons. (E), Mitochondrial Ca²⁺ efflux kinetics was quantified by measuring the duration of 70% [Ca²⁺]_mt recovery relative to its peak elevation (T₇₀), and compared before and after treatment with CGP37157. Data are presented as mean ± SEM, n=9; ***p<0.001, two-tailed paired Student’s t-test.