Calcium activation of heart mitochondrial oxidative phosphorylation -: Rapid kinetics of m(V) over dot O2, NADH, and light scattering

Parallel activation of heart mitochondria NADH and ATP production by Ca2+ has been shown to involve the Ca2+-sensitive dehydrogenases and the F0F1-ATPase, In the current study we hypothesize that the response time of Ca2+-activated ATP production is rapid enough to support step changes in myocardial workload (similar to 100 ms). To test this hypothesis, the rapid kinetics of Ca2+ activation of m(V)over dot (O2) [NADH], and light scattering were evaluated in isolated porcine heart mitochondria at 37 degreesC using a variety of optical techniques. The addition of Ca2+ was associated with an initial response time (IRT) of m(V)over dot (O2), that was dose-dependent with a minimum IRT of 0.27 +/- 0.02 a (n = 41) at 535 mM Ca2+. The IRTs for NADH fluorescence and light scattering in response to Ca2+ additions were similar to m(V)over dot (O2). The Ca2+ IRT for m(V)over dot(O2) was significantly shorter than 1.6 mM ADP (2.36 +/- 0.47 a; p less than or equal to 0.001, n = 13), 2.2 mM P-i (2.32 +/- 0.29,p less than or equal to 0.001, n = 13), or 10 mM creatine (15.6. +/- 1.18 s,p less than or equal to 0.001, n = 18) under similar experimental conditions. Calcium effects were inhibited with 8 muM ruthenium red (2.4 +/- 0.31 s;p less than or equal to 0.001, n = 16) and reversed with EG;TA (1.6 +/- 0.44;p less than or equal to 0.01, n = 6), Estimates of Ca2+ uptake into mitochondria using optical Ca2+ 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 Ca2+ can modify ATP production, via an increase in matrix Ca2+ content, rapidly enough to support cardiac work transitions in vivo.