CAMP AND CA2-RAT HEPATOCYTES TO ADRENALINE( INVOLVEMENT IN THE MITOCHONDRIAL RESPONSE OF CULTURED FETAL)

The effect of adrenaline on the control of respiratory activity of mit ochondria from fetal hepatocytes in primary culture was studied. In th e absence of adrenaline, the respiratory control ratio (RCR) of mitoch ondria increased during the first 3 days of culture due to a decrease in the rate of state 4 respiration. The presence of adrenaline in the incubation medium further increased the mitochondrial RCR through a de crease in the rate of respiration in state 4 and to an increase in the respiration rate in state 3. The effect of adrenaline was mimicked by dibutyryl-cAMP, forskolin, and isobutyl methyl xanthine. All these co mpounds increased cAMP concentrations, suggesting that cAMP may be inv olved in the effect of adrenaline. The increase in intracellular free Ca2+ concentrations caused by phenylephrine, vasopressin, or thapsigar gin was also accompanied by an increase in the RCR, suggesting that bo th phenomena are associated. Dibutyryl-cAMP also increased free Ca2+ c oncentrations, suggesting that the effects of cAMP may be mediated by free Ca2+ concentrations. Adrenaline, dibutyryl-cAMP, phenylephrine, v asopressin, and thapsigargin promoted adenine nucleotide accumulation in mitochondria; this may be an intermediate step in the activation of mitochondrial respiratory function. These results suggest that the st imulatory effect of adrenaline on mitochondrial maturation in cultured fetal rat hepatocytes may be exerted through a mechanism in which bot h cAMP and Ca2+ act as second messengers. It is concluded that the eff ect of adrenaline on mitochondrial maturation is exerted by both alpha - and beta-adrenergic mechanisms and is mediated by the increase in ad enine nucleotide contents of mitochondria. (C) 1997 Academic Press.