Mitochondria buffer physiological calcium loads in cultured rat dorsal root ganglion neurons

John L. Werth, Stanley A Thayer

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We sought to determine whether low-affinity, high-capacity mitochondrial Ca2+ uptake contributes to buffering physiological Ca2+ loads in sensory neurons. Intracellular free calcium concentration ([Ca2+](i)) and intracellular free hydrogen ion concentration ([H+](i)) were measured in single rat dorsal root ganglion (DRG) neurons grown in primary culture using indo-1 and carboxy-SNARF-based dual emission microfluorimetry. Field potential stimulation evoked action potential-mediated increases in [Ca2+](i). Brief trains of action potentials elicited [Ca2+](i) transients that recovered to basal levels by a single exponential process. Trains of >25 action potentials elicited larger increases in [Ca2+](i), recovery from which consisted of three distinct phases. During a rapid initial phase [Ca2+](i) decreased to a plateau level (450-550 nM). The plateau was followed by a slow return to basal [Ca2+](i). [Ca2+](i) transients elicited by 40-50 action potentials in the presence of the mitochondrial uncoupler carbonyl cyanide chlorophenyl hydrazone (CCCP), or the electron transport inhibitor antimycin A 1, lacked the plateau, and the recovery to basal [Ca2+](i) consisted of a single slow phase. Depolarization with 50 mM K+ produced a multiphasic [Ca2+](i) transient and increased [H+](i) from 74 ± 3 to 107 ± 8 nM. The rise in [H+](i) was dependent upon extracellular Ca2+ and was inhibited by mitochondrial poisons. With mitochondrial Ca2+ buffering pharmacologically blocked, the recovery to basal [Ca2+](i) was unaffected by removal of extracellular Na+. We conclude that large Ca2+ loads are initially buffered by fast mitochondrial sequestration that effectively uncouples electron transport from ATP synthesis, leading to an increase in [H+](i). Small Ca2+ loads are buffered by a nonmitochondrial, Na+-independent process.

Original languageEnglish (US)
Pages (from-to)348-356
Number of pages9
JournalJournal of Neuroscience
Issue number1
StatePublished - Jan 1994


  • action potentials
  • intracellular calcium
  • intracellular pH
  • metabolism
  • mitochondria
  • sensory neuron


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