The permeability of isolated rat-liver mitochondria at 0° to the metabolites pyruvate, succinate, citrate, phosphate, adenosine 5′-phosphate and adenosine triphosphate

Abstract

The distribution of solutes between isolated rat-liver mitochondria and the suspension medium at 0[degree] was studied by centrifuging and analyzing the sedimented pellet and supernatant fluid. The distribution of the Na salts of pyruvate, succinate, citrate, phosphate, adenosine 5[image]-phosphate and adenosine triphosphate were measured over a wide range of external concentration. The volume of extraparticulate fluid in the pellet was estimated, and the distribution of sucrose was also measured. With mM salt in the medium, marked uptakes of succinate, citrate and phosphate by the mitochondria were observed. The increases in concentration of these anions in the mitochondria were 4 to 10 times the concentrations in the medium. About 2/3 of the mitochondrial water was accessible to sucrose, and the space accessible to pyruvate, succinate and citrate was of the same order. The mitochondria were rather more accessible to phosphate than they were to sucrose. They were much less accessible to adenosine 5[image]-phosphate and to adenosine triphosphate, the permeability to the latter being 1/4 of that to sucrose. With each salt, the penetration of Na was somewhat greater than the penetration of the anion. Part of the difference may be due to the loss of endogenous K from the mitochondria. The changes in water content of the mitochondria when they were suspended in solutions of the sodium adenosine phosphates were not consistent with osmotic considerations based on the measured distribution of solutes.