Hormonal regulation of mitochondrial function. Description of a system capable of mimicking several effects of glucagon.

Isolated rat liver mitochondria were incubated at 0 degrees C in a medium consisting of 225 mM sucrose, 10 mM KCl, 1 mM EDTA, 10 mM KH2PO4, 5 mM MgCl2 and 10 mM Tris-HCl, pH 7.4 (buffer 1) for 10 min, centrifuged and resuspended in 0.3 M sucrose. This treatment resulted in a stimulation of mitochondrial functions, mimicking several of the effects that follow glucagon treatment of the intact rat or isolated hepatocytes. Both phosphate and potassium are required for this effect; the addition of magnesium serves to enhance it. Mitochondrial respiration is essential for the development of the activated state as the stimulation is blocked by increasing concentrations of rotenone in the incubation. The intramitochondrial ATP/ADP ratio is increased, but when this increase was prevented by including low levels of rotenone or oligomycin in buffer 1, the stimulation of mitochondrial function was not diminished, thus demonstrating that an increased ATP/ADP ratio is not essential for activation. The rate of citrulline formation was unaffected by buffer 1 treatment unless glutamate was also included in the medium, indicating that control of this mitochondrial function differs from other functions studied.