| Abstract: | The effects of ADP, carboxyatractyloside (CAT) and the local anaesthetic nupercaine on the energy-dependent Ca2+ uptake by rat liver mitochondria oxidizing succinate in the presence of oligomycin were compared, using incubation media of 320 mosM and 120 mosM tonicities. In hypotonic media the mitochondrial Ca2+ capacity was increased by 50%, and the mitochondria were more stable to the damaging effects of Ca + Pi. In the presence of ADP the Ca2+ capacities of mitochondria increased both in normotonic and hypotonic media; however, the absolute amounts of calcium consumed were levelled off. CAT abolished the effect of ADP on the mitochondrial Ca2+ uptake and equalized the Ca2+ capacities of rat liver mitochondria in the both media. The local anaesthetic nupercaine also increased the Ca2+ capacity of mitochondria. The effects of nupercaine and ADP were additive. CAT abolished the effect of ADP but not that of nupercaine. Measurements of the intramitochondrial contents of adenine nucleotides showed that in 120 mosM media there was a significant increase in the intramitochondrial content of ATP and the total pool of adenine nucleotides. It was concluded that in hypotonic media the mitochondrial adenine nucleotide carrier exists predominantly in the m-conformation thus facilitating the energization of mitochondria. |
