Regulation of cardiac mitochondrial calcium by average extramitochondrial calcium.
A system to perifuse isolated rat heart mitochondria was designed to study the relationship between mitochondrial matrix free Ca2+ and extramitochondrial free Ca2+ under conditions in which the latter concentration could oscillate over a range typical of that expected in vivo. We tested the hypothesis that the level of intramitochondrial Ca2+ responds to the average extramitochondrial Ca2+ in the heart. Mitochondria were immobilized within an optical chamber for measurement of endogenous NAD(P)H and fura 2 fluorescence. NAD(P)H increased significantly on provision of substrates and decreased reversibly in the presence of ADP, indicating maintenance intact coupled respiration by this preparation. Matrix free Ca2+ was measured using fura 2-loaded mitochondria and, in parallel experiments, media free Ca2+ was measured with fura 2 in the absence of mitochondria. Oscillation of extramitochondrial Ca2+ from < 0.1 microM to approximately 2 microM at frequencies of 0.5, 1.0, and 1.25 cycles/s produced steady-state levels of matrix Ca2+ that were independent of frequency but proportional to the average media free Ca2+ concentration. Matrix Ca2+ increased to a steady state on an increase in the extramitochondrial average Ca2+ concentration with a half-time (t1/2) of approximately 2 min at 22 degrees C. Oscillation of mitochondrial Ca2+ was not observed under any conditions tested. The data are taken to indicate that in vivo, the concentration of mitochondrial matrix free Ca2+ is a steady state that is proportional to the average extramitochondrial Ca2+ concentration and that changes in the latter represent a mechanism of signal transduction from the cytosol to the mitochondrial matrix.
Leisey
J R
JR
Department of Cellular and Molecular Physiology, Milton S. Hershey Medical Center, Pennsylvania State University, Hershey 17033.
Grotyohann
L W
LW
Scott
D A
DA
Scaduto
R C
RC
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000502:physiology*; D003470:Culture Media / Q000737:chemistry; D005109:Extracellular Matrix / Q000378:metabolism; D005456:Fluorescent Dyes; D016257:Fura-2; D008856:Microscopy, Fluorescence; D008929:Mitochondria, Heart / Q000378:metabolism*; D009249:NADP / Q000378:metabolism; D010477:Perfusion / Q000379:methods
D003470:Culture Media; D005456:Fluorescent Dyes; D009249:NADP; D002118:Calcium; D016257:Fura-2