Fig. 7: Mitochondrial Ca²⁺ buffering reduces the coupling between Ca²⁺ influx and activation of the sAHP current in pyramidal neurons.

a Traces depict the sAHP membrane current (I_sAHP) in a patch-clamped hippocampal CA1 pyramidal neuron in response to step depolarizations (−85 mV to −5 mV) of progressively increasing duration. Blocking mitochondrial Ca²⁺ uptake with Ru360 substantially enlarged the I_sAHP evoked by long, but not short, step depolarizations. b Summary data showing that Ru360 significantly increased the evoked outward current area following long depolarizing steps (control: n = 9, N = 9; Ru360: n = 12, N = 9; 200 ms pulse, unpaired t test, p = 0.849; 400 ms pulse, unpaired t test, p = 0.705; 600 ms pulse, unpaired t test, p = 0.207; 800 ms pulse, unpaired t test, p = 0.064; 1000 ms pulse, unpaired t test with Welch’s correction, p = 0.0365; 1200 ms pulse, unpaired t test, p = 0.041; 1400 ms pulse, unpaired t test with Welch’s correction, p = 0.004; 1600 ms pulse, unpaired t test, p = 0.01; 1800 ms pulse, unpaired t test with Welch’s correction, p = 0.009; 2000 ms pulse, unpaired t test, p = 0.003). c Membrane currents in control and Ru360 produced by two voltage ramps (r1 & r2) from -135 to −75 mV, measured with (sweep 2 [s2]) and without (sweep 1 [s1]) a preceding step depolarization. d Current-voltage (I-V) relationship for the I_sAHP, measured from ramp 1 and ramp 2, in the presence and absence of Ru360. The I_sAHP current has a reversal potential consistent with a potassium current and is significantly larger in Ru360 (ramp 2 current at −80 mV, control: n = 9, N = 9; Ru360: n = 9, N = 8; unpaired t test, p = 0.049). The I-V plot for the I_sAHP was produced by subtracting the voltage-ramp currents of sweep 1 from sweep 2. e Increasing the Ca²⁺ buffering capacity of the cytosol via intracellular dialysis of 10 mM BAPTA largely prevented the enhancement of the evoked I_sAHP produced by disrupting mitochondrial Ca²⁺ buffering with Ru360. f In the presence of intracellular BAPTA, Ru360 had no significant effect on the evoked outward current area, except during the 1400 ms step depolarization (BAPTA: n = 6, N = 3; BAPTA + Ru360: n = 5, N = 2; 200 ms pulse, unpaired t test, p = 0.159; 400 ms pulse, unpaired t test, p = 0.22; 600 ms pulse, unpaired t test, p = 0.23; 800 ms pulse, unpaired t test, p = 0.18; 1000 ms pulse, unpaired t test with Welch’s correction, p = 0.22; 1200 ms pulse, Mann-Whitney test, p = 0.082; 1400 ms pulse, Mann-Whitney test, p = 0.03; 1600 ms pulse, unpaired t test, p = 0.065; 1800 ms pulse, unpaired t test, p = 0.29; 2000 ms pulse, Mann-Whitney test, p = 0.247). Summary data presented as the mean ± SEM. *P < 0.05, **P < 0.01, ***P < 0.001. The number of cell replicates is shown in the graphs as well as the ‘n’ value in the text. The number of animal replicates is represented by the ‘N’ value.