Characterization of mitochondrial membrane fragments resulting from spontaneous swelling: novel stimulation of NADH-dependent respiration by carboxylic acids.

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.