Functional studies on in situ-like mitochondria isolated in the presence of polyvinyl pyrrolidone.

ABSTRACT

Mitochondria isolated and maintained in sucrose mannitol medium show a large intermembrane space and a condensed matrix unlike the appearance of in situ mitochondria. Mitochondria resembling in situ organelles are obtained when the isolation medium is supplemented with certain macromolecules such as polyvinyl pyrrolidone. We found that the in situ appearance was acquired also by the conventionally isolated mitochondria when they were exposed to 2% polyvinyl pyrrolidone supplemented medium. Paradoxically, however, these in situ looking mitochondria proved functionally inferior in that their brief incubation without substrates led to a marked loss of their ability to respire with subsequently added substrates such as pyruvate, acylcarnitines or glutamate. The oxidation of succinate was, however, not so affected. This phenomenon was shared by heart and skeletal muscle mitochondria of different animal species but not by rat liver mitochondria. The inhibition of respiration could not be related to the failure to oxidize NADH, to the tieing up of mitochondrial free CoASH, or to the increased matrix space of mitochondria that was observed in the presence of polyvinyl pyrrolidone. The polyvinyl pyrrolidone-exposed mitochondria regained their respiratory ability on being freed from polyvinyl pyrrolidone. The same phenomenon was seen also when the medium contained 2% albumin or 20% Ficoll.