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A Reevaluation of the Role of Mitochondria in Neuronal Ca 2+ Homeostasis
Author(s) -
Budd S. L.,
Nicholls D. G.
Publication year - 1996
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1996.66010403.x
Subject(s) - oligomycin , depolarization , protonophore , biophysics , membrane potential , rotenone , mitochondrion , cytoplasm , biology , atp synthase , adenosine triphosphate , chemistry , biochemistry , microbiology and biotechnology , atpase , enzyme
The ability of mitochondrial Ca 2+ transport to limit the elevation in free cytoplasmic Ca 2+ concentration in neurones following an imposed Ca 2+ load is reexamined. Cultured cerebellar granule cells were monitored by digital fura‐2 imaging. Following KCI depolarization, addition of the protonophore carbonylcyanide m ‐chlorophenylhydrazone (CCCP) to depolarize mitochondria released a pool of Ca 2+ into the cytoplasm in both somata and neurites. No CCCP‐releasable pool was found in nondepolarized cells. Although the KCI‐evoked somatic and neurite Ca 2+ concentration elevations were enhanced when CCCP was present during KCI 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 KCI depolarization, consistent with the abolition of mitochondrial Ca 2+ transport; however, paradoxically the KCI‐evoked Ca 2+ elevation is decreased. It is concluded that the CCCP‐induced increase in cytoplasmic Ca 2+ response to KCI is due to inhibition of nonmitochondrial ATP‐dependent transport and that mitochondrial Ca 2+ transport enhances entry of Ca 2+ , perhaps by removing the cation from cytoplasmic sites responsible for feedback inhibition of voltage‐activated Ca 2+ channel activity.