Quantitative analysis of mitochondrial Ca2+ uptake and release pathways in sympathetic neurons. Reconstruction of the recovery after depolarization-evoked [Ca2+]i elevations.
Rate equations for mitochondrial Ca2+ uptake and release and plasma membrane Ca2+ transport were determined from the measured fluxes in the preceding study and incorporated into a model of Ca2+ dynamics. It was asked if the measured fluxes are sufficient to account for the [Ca2+]i recovery kinetics after depolarization-evoked [Ca2+]i elevations. Ca2+ transport across the plasma membrane was described by a parallel extrusion/leak system, while the rates of mitochondrial Ca2+ uptake and release were represented using equations like those describing Ca2+ transport by isolated mitochondria. Taken together, these rate descriptions account very well for the time course of recovery after [Ca2+]i elevations evoked by weak and strong depolarization and their differential sensitivity to FCCP, CGP 37157, and [Na+]i. The model also leads to three general conclusions about mitochondrial Ca2+ transport in intact cells: (1) mitochondria are expected to accumulate Ca2+ even in response to stimuli that raise [Ca2+]i only slightly above resting levels; (2) there are two qualitatively different stimulus regimes that parallel the buffering and non-buffering modes of Ca2+ transport by isolated mitochondria that have been described previously; (3) the impact of mitochondrial Ca2+ transport on intracellular calcium dynamics is strongly influenced by nonmitochondrial Ca2+ transport; in particular, the magnitude of the prolonged [Ca2+]i elevation that occurs during the plateau phase of recovery is related to the Ca2+ set-point described in studies of isolated mitochondria, but is a property of mitochondrial Ca2+ transport in a cellular context. Finally, the model resolves the paradoxical finding that stimulus-induced [Ca2+]i elevations as small as approximately 300 nM increase intramitochondrial total Ca2+ concentration, but the steady [Ca2+]i elevations evoked by such stimuli are not influenced by FCCP.
Colegrove
S L
SL
Department of Neuroscience, Case Western Reserve University, Cleveland, Ohio, USA.
Albrecht
M A
MA
Friel
D D
DD
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000493:pharmacokinetics*; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D002998:Clonazepam / Q000031:analogs & derivatives / Q000494:pharmacology; D004594:Electrophysiology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008928:Mitochondria / Q000378:metabolism*; D009474:Neurons / Q000737:chemistry* / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D011892:Rana catesbeiana; D019831:Sodium-Calcium Exchanger / Q000378:metabolism; D013268:Stimulation, Chemical; D013564:Sympathetic Nervous System / Q000166:cytology; D013841:Thiazepines / Q000494:pharmacology; D014475:Uncoupling Agents / Q000494:pharmacology
D019831:Sodium-Calcium Exchanger; D013841:Thiazepines; D014475:Uncoupling Agents; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D002998:Clonazepam; C079032:CGP 37157; D011188:Potassium; D002118:Calcium