A reevaluation of the role of mitochondria in neuronal Ca2+ homeostasis.
The ability of mitochondrial Ca2+ transport to limit the elevation in free cytoplasmic Ca2+ concentration in neurones following an imposed Ca2+ load is reexamined. Cultured cerebellar granule cells were monitored by digital fura-2 imaging. Following KCl depolarization, addition of the protonophore carbonylcyanide m-chlorophenylhydrazone (CCCP) to depolarize mitochondria released a pool of Ca2+ into the cytoplasm in both somata and neurites. No CCCP-releasable pool was found in nondepolarized cells. Although the KCl-evoked somatic and neurite Ca2+ concentration elevations were enhanced when CCCP was present during KCl depolarization, this was associated with a collapsed ATP/ADP ratio. In the presence of the ATP synthase inhibitor oligomycin, glycolysis maintained high ATP/ADP ratios for at least 10 min. The further addition of the mitochondrial complex I inhibitor rotenone led to a collapse of the mitochondrial membrane potential, monitored by rhodamine-123, but had no effect on ATP/ADP ratios. In the presence of rotenone/oligomycin, no CCCP-releasable pool was found subsequent to KCl depolarization, consistent with the abolition of mitochondrial Ca2+ transport; however, paradoxically the KCl-evoked Ca2+ elevation is decreased. It is concluded that the CCCP-induced increase in cytoplasmic Ca2+ response to KCl is due to inhibition of nonmitochondrial ATP-dependent transport and that mitochondrial Ca2+ transport enhances entry of Ca2+, perhaps by removing the cation from cytoplasmic sites responsible for feedback inhibition of voltage-activated Ca2+ channel activity.
Department of Biochemistry, University of Dundee, Scotland.
S L
SL
Budd
D G
DG
Nicholls
D000255:Adenosine Triphosphate / Q000502:physiology; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D002531:Cerebellum / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D004734:Energy Metabolism / Q000187:drug effects; D006706:Homeostasis / Q000187:drug effects; D007476:Ionophores / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D008928:Mitochondria / Q000187:drug effects / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D009840:Oligomycins / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D011522:Protons; D051381:Rats; D017208:Rats, Wistar; D014475:Uncoupling Agents / Q000494:pharmacology
D007476:Ionophores; D009840:Oligomycins; D011522:Protons; D014475:Uncoupling Agents; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D011189:Potassium Chloride; D000255:Adenosine Triphosphate; D002118:Calcium