ABSTRACT
Rotenone-sensitive, uncoupler-insensitive, NADH-dependent respiration was demonstrated in osmotically inactive fragments of the mitochondrial inner-membrane obtained following high amplitude (spontaneous) swelling. This NADH-dependent respiration as well as mitochondrial ATPase activity was stimulated by ligands which are known to be transported by specific transporters/mechanisms. The ligands capable of this anomalous respiratory control included several intermediates of the citric acid cycle, besides non-metabolizable ligands including lactate, cations such as K+ and Ca2+. The interaction between NADH-dependent respiration and these ligands, as manifested by stimulation of respiration, was strongly ionic strength-dependent. The thermodynamic relationship between respiratory control and stimulation of transport ATPase by the relevant transportable ligands could also be demonstrated in the conventional (rat liver) microsomes. These experimental results offer a novel experimental base for search into an intra-membranous mechanism of energy transduction.
Subject(s)
Animals , Biological Transport, Active , Mitochondria, Liver/metabolism , Mitochondrial Swelling , NAD/metabolism , Osmosis , Oxygen Consumption , Phosphorylation , Rats , Rats, Inbred StrainsABSTRACT
Metabolically induced high amplitude swelling of rat liver mitochondria has been found to result in the formation of a heterogeneous population of mitochondrial membranes consisting of right side-out particles with occluded fumarase activity and inside-out particles/fragments capable of NADH-dependent respiration. This rotenone-sensitive, uncoupler-insensitive, NADH-dependent respiration was specifically and instantaneously stimulated by several ligands such as glutamate and malate (which can be metabolized) and, interestingly, even lactate (which could not be metabolized by the swollen mitochondria). These observations suggest that high amplitude swelling results in a novel type of control of respiration in these fragments.