Roles of mitochondria and temperature in the control of intracellular calcium in adult rat sensory neurons

We recorded Ca2+ current and intracellular Ca2+ ([Ca2+]i) in isolated adult rat dorsal root ganglion (DRG) neurons at 20 and 30 °C. In neurons bathed in tetraethylammonium and dialyzed with cesium, warming reduced resting [Ca2+]i from 87 to 49 nM and the time constant of the decay of [Ca2+]i transients (τr) from 1.3 to 0.99 s (Q10 = 1.4). The Buffer Index, the ratio between Ca2+ influx and Δ[Ca2+]i∫ICa dt/Δ[Ca2+]i, increased two- to threefold with warming. Neither inhibition of the plasma membrane Ca2+-ATPase by intracellular sodium orthovanadate nor inhibition of Ca2+ uptake by the endoplasmic reticulum by thapsigargin plus ryanodine were necessary for the effects of warming on these parameters. In contrast, inhibition of the mitochondrial Ca2+ uniporter by intracellular ruthenium red largely reversed the effects of warming. Carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone (FCCP, 500 nM) increased resting [Ca2+]i at 30 °C. Ten millimolar intracellular sodium prolonged the recovery of [Ca2+]i transients to 10–40 s. This effect was reversed by an inhibitor of mitochondrial Na+/Ca2+-exchange (CGP 37157, 10 μM). Thus, mitochondrial Ca2+ uptake is necessary for the temperature-dependent increase in Ca2+ buffering and mitochondrial Ca2+ fluxes contribute to the control of [Ca2+]i between 50 and 150 nM at 30 °C.