Ca2+-induced accumulation of pyrophosphate in mitochondria during acetate metabolism

Abstract

The mechanism of pyrophosphate (PPi) accumulation in rat liver during acetate metabolism was investigated. Perfusion of the liver with acetate in the presence of noradrenaline and glucagon induced marked accumulation of PPi (2 mumol/g of liver, 200 times that of control). In contrast, perfusion with glutamine, which generates PPi only in the cytosol, caused little accumulation of PPi, even in the presence of the two hormones. The site of PPi accumulation was shown to be the mitochondria by the finding that isolated mitochondria from the liver perfused with acetate and the hormones contained 50 nmol of PPi/mg of protein. The addition of an uncoupler to mitochondria with accumulated PPi caused gradual decrease in their PPi content, with concomitant release of a stoichiometric amount of Ca2+. Similar accumulation of PPi was observed when isolated mitochondria were incubated with acetate and Ca2+. These results show that an increase in cytosolic Ca2+ caused by the co-administration of the two hormones induced uptake of the ion into mitochondria, and that PPi accumulated in mitochondria only when it was generated in the organelles with an elevated concentration of Ca2+. High mitochondrial concentrations of Ca2+ are considered to inhibit inorganic pyrophosphatase through the formation of a stable complex, CaPPi-. Mitochondria with accumulated PPi had normal respiratory activities, and their adenine nucleotide concentrations were increased 2-fold rather than being decreased, the increases also being considered to be caused by their high concentration of Ca2+.

Pyrophosphate metabolism in the perfused heart and isolated heart mitochondria and its role in regulation of mitochondrial function by calcium

“…Unlike the situation in liver (Davidson and Halestrap, 1988;Yamada et al, 1988;Inoue et al, 1989), no significant increases in tissue [PPJ] are observed in response to any of the treatments.…”

“…Treatment of the perfused liver (Yamada et al, 1988;Inoue et al, 1989) and isolated hepatocytes (Davidson and Halestrap, 1988) with hormones that raise intracellular [Ca2"], or exposure of isolated mitochondria to physiological concentrations of Ca2l (Davidson and Halestrap, 1987), leads to a substantial increase in mitochondrial-matrix [PPJ]. This occurs as the result of the inhibition of mitochondrial pyrophosphatase by Ca2+, an effect mediated by the formation of CaPPi, which is a very potent competitive inhibitor of the enzyme with respect to MgPPi (Davidson and Halestrap, 1989;Baykov et al, 1989a).…”

Isotonic crystalloid solutions: a structured review of the literature

“…Ringer's acetate solutions may create metabolic alterations. Inoue and colleagues 59 explored acetate metabolism using a liver rat model and showed that Ringer's acetate was associated with pyrophosphate accumulation inside the mitochondria, a phenomenon that could potentially lead to mitochondrial dysfunction. In the past, Ringer's acetate was used routinely in haemodialysis units, but these limitations and studies suggesting a vasodilatory and cardio-depressant effect of acetate 60 -64 have restricted its use.…”