Dependence of cardiac mitochondrial pyruvate dehydrogenase activity on intramitochondrial free Ca2+ concentration

Abstract

(1) The free Ca2l concentration of the matrix of rat heart mitochondria ([Ca2`]m) was determined from the fluorescence of internalized indo-1. The value of the Kd of indo-I-Ca2" in the mitochondrial matrix was determined to be 95 nm, on the basis of equilibration of [Ca2"]m with the extramitochondrial free Ca2l ([Ca2"].) in the presence of rotenone, nigericin, valinomycin and Br-A23187. (2) [Ca2"]m responded to energization/de-energization protocols, the inhibition of Ca2"-uptake by Ruthenium Red and the potentiation of Ca2+-efflux by Na+ in a manner which was consistent with the known kinetic properties of the mitochondrial Ca2+-transport processes. INTRODUCTIONCa2l ions serve not only to couple excitation to contraction in heart muscle (see Katz, 1970), thereby creating an energy demand, but also to activate the process of oxidative phosphorylation, thereby ensuring an enhanced energy supply. The latter process involves the activation by Ca2l ions of pyruvate dehydrogenase phosphatase (Denton et al., 1972;Pettit et al., 1972), NAD+-linked isocitrate dehydrogenase (Denton et al., 1978) and 2-oxoglutarate dehydrogenase (McCormack & Denton, 1979;Lawlis & Roche, 1980). Each of these dehydrogenases catalyses a non-equilibrium reaction, and activation may tend to maintain elevated mitochondrial NADH/NAD+ ratios during periods of high work-load, thus maximizing the redox driving force for oxidative phosphorylation and flux through that process (see Koretsky & Balaban, 1987). These relations have been reviewed by Hansford (1980Hansford ( , 1985. Each of these dehydrogenase systems is present within the permeability barrier of the mitochondrial inner membrane, leading (Sheu & Fozzard, 1982;McCormack & England, 1983), would elicit enhanced dehydrogenase activity, and enhanced energy transduction by oxidative phosphorylation. Evidence in favour of this proposal has been recently reviewed (Denton & McCormack, 1985;Hansford, 1985).Although there is good agreement on the relationship between the fraction of pyruvate dehydrogenase existing in the active dephosphorylated form (PDHA; see reviews by Reed, 1981;Wieland, 1983) in isolated cardiac mitochondria and the concentration of free ionized Ca2" ([Ca2+]O) in the suspending medium (Hansford & Cohen, 1978;Hansford, 1981) al., 1982;Hansford & Castro, 1982), and the insertion of the metallochromic indicator Arsenazo III into the mitochondria by a permeabilization/resealing protocol (Hayat & Crompton, 1987). The precision of the 'nullpoint' technique is limited by the small absorbance changes seen with the extramitochondrial metallochromic indicator when mitochondrial Ca2" loads low enough to be of relevance to dehydrogenase regulation are investigated, whereas the permeability/resealing protocol may, theoretically at least, perturb the matrix composition, especially with respect to metal ions and low-molecular-mass cofactors. R. Moreno-Sainchez and R. G. Hansford (Tsien et al., 1982;Grynkiewicz et al., 1985) have been applied to the study of [Ca2"]m in suspensions of isolat...

Absence of Malonyl Coenzyme A Decarboxylase in Mice Increases Cardiac Glucose Oxidation and Protects the Heart From Ischemic Injury

“…Indeed, inhibition of pyruvate oxidation in the heart can readily occur independently of PDK phosphorylation of PDC. 40,41 We have also previously shown that glucose oxidation rates in the mouse heart can be dramatically altered independently of PDK phosphorylation and inhibition of PDC and that flux of pyruvate through PDC is regulated by fatty acid oxidation reaction products. 42 In the case of hearts from the mcd Ϫ/Ϫ mice, these fatty acid oxidation reaction products would be dramatically reduced after ischemia relative to wild-type hearts, likely relieving the inhibition of PDC.…”

The control of brain mitochondrial energization by cytosolic calcium: The mitochondrial gas pedal

“…• Ca 2þ Activation of OXPHOS: This hypothesis is based on the findings that not only the extramitochondrial ATPases, but also mitochondrial dehydrogenases, such as pyruvate dehydrogenase (PDH) (26), NADH-isocitrate dehydrogenase (ICDH) (27), and a-ketoglutarate dehydrogenase (a-KGDH) (28), can be activated by increased [Ca 2þ ] (Fig. 1).…”

Altered Ca2+Signaling and Mitochondrial Deficiencies in Hippocampal Neurons of Trisomy 16 Mice: A Model of Down’s Syndrome

“…؉ ratio in diploid and Ts16 neurons Increases in [Ca 2ϩ ] i may lead to intramitochondrial Ca 2ϩ accumulation, which in turn may increase respiration via activation of different intramitochondrial enzymes of the citrate cycle, namely pyruvate dehydrogenase, NAD ϩ -isocitrate dehydrogenase, and ␣-ketoglutarate dehydrogenase (Moreno-Sánchez and Hansford, 1988;Richter and Kass, 1991). Increased activity of the citrate cycle results in an increase in the NADH/NAD ϩ ratio (Duchen et al, 1993).…”