Ca21 activation of heart mitochondrial oxidative phosphorylation: role of the F0/F1-ATPase

Territo, Paul R., Vamsi K. Mootha, Stephanie A. French, and Robert S. Balaban. Ca21 activation of heart mitochondrial oxidative phosphorylation: role of the F0/F1ATPase. Am. J. Physiol. Cell Physiol. 278: C423–C435, 2000.—Ca21 has been postulated as a cytosolic second messenger in the regulation of cardiac oxidative phosphorylation. This hypothesis draws support from the well-known effects of Ca21 on muscle activity, which is stimulated in parallel with the Ca21-sensitive dehydrogenases (CaDH). The effects of Ca21 on oxidative phosphorylation were further investigated in isolated porcine heart mitochondria at the level of metabolic driving force (NADH or Dc) and ATP production rates (flow). The resulting force-flow (F-F) relationships permitted the analysis of Ca21 effects on several putative control points within oxidative phosphorylation, simultaneously. The F-F relationships resulting from additions of carbon substrates alone provided a model of pure CaDH activation. Comparing this curve with variable Ca21 concentration ([Ca21]) effects revealed an approximate twofold higher ATP production rate than could be explained by a simple increase in NADH or Dc via CaDH activation. The half-maximal effect of Ca21 at state 3 was 157 nM and was completely inhibited by ruthenium red (1 μM), indicating matrix dependence of the Ca21 effect. Arsenate was used as a probe to differentiate between F0/F1-ATPase and adenylate translocase activity by a futile recycling of ADP-arsenate within the matrix, catalyzed by the F0/F1-ATPase. Ca21 increased the ADP arsenylation rate more than twofold, suggesting a direct effect on the F0/F1ATPase. These results suggest that Ca21 activates cardiac aerobic respiration at the level of both the CaDH and F0/F1-ATPase. This type of parallel control of both intermediary metabolism and ATP synthesis may provide a mechanism of altering ATP production rates with minimal changes in the high-energy intermediates as observed in vivo.