title: Calcium activation of heart mitochondrial oxidative phosphorylation: rapid kinetics of mVO2, NADH, AND light scattering.
abstract: Parallel activation of heart mitochondria NADH and ATP production by Ca(2+) has been shown to involve the Ca(2+)-sensitive dehydrogenases and the F(0)F(1)-ATPase. In the current study we hypothesize that the response time of Ca(2+)-activated ATP production is rapid enough to support step changes in myocardial workload ( approximately 100 ms). To test this hypothesis, the rapid kinetics of Ca(2+) activation of mV(O(2)), [NADH], and light scattering were evaluated in isolated porcine heart mitochondria at 37 degrees C using a variety of optical techniques. The addition of Ca(2+) was associated with an initial response time (IRT) of mV(O(2)) that was dose-dependent with a minimum IRT of 0.27 +/- 0.02 s (n = 41) at 535 nm Ca(2+). The IRTs for NADH fluorescence and light scattering in response to Ca(2+) additions were similar to mV(O(2)). The Ca(2+) IRT for mV(O(2)) was significantly shorter than 1.6 mm ADP (2.36 +/- 0.47 s; p < or = 0.001, n = 13), 2.2 mm P(i) (2.32 +/- 0.29, p < or = 0.001, n = 13), or 10 mm creatine (15.6.+/-1.18 s, p < or = 0.001, n = 18) under similar experimental conditions. Calcium effects were inhibited with 8 microm ruthenium red (2.4 +/- 0.31 s; p < or = 0.001, n = 16) and reversed with EGTA (1.6 +/- 0.44; p < or = 0.01, n = 6). Estimates of Ca(2+) uptake into mitochondria using optical Ca(2+) indicators trapped in the matrix revealed a sufficiently rapid uptake to cause the metabolic effects observed. These data are consistent with the notion that extramitochondrial Ca(2+) can modify ATP production, via an increase in matrix Ca(2+) content, rapidly enough to support cardiac work transitions in vivo.
authors.affiliation: Laboratory of Cardiac Energetics, NHLBI, National Institutes of Health, Bethesda, Maryland 20892-1061, USA. territop@zeus.nhbli.nih.gov
authors.forename: P R
authors.initials: PR
authors.lastname: Territo
authors.forename: S A
authors.initials: SA
authors.lastname: French
authors.forename: M C
authors.initials: MC
authors.lastname: Dunleavy
authors.forename: F J
authors.initials: FJ
authors.lastname: Evans
authors.forename: R S
authors.initials: RS
authors.lastname: Balaban
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology; D020013:Calcium Signaling; D003600:Cytosol / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D007700:Kinetics; D008027:Light; D008929:Mitochondria, Heart / Q000378:metabolism* / Q000648:ultrastructure; D009206:Myocardium / Q000648:ultrastructure; D009243:NAD / Q000378:metabolism*; D010085:Oxidative Phosphorylation; D010101:Oxygen Consumption; D012542:Scattering, Radiation; D013552:Swine
chemical_list: D009243:NAD; D002118:Calcium