ION TRANSPORT BY HEART MITOCHONDRIA .11. SPONTANEOUS AND INDUCED PERMEABILITY OF HEART MITOCHONDRIA TO CATIONS

1. 1. Isolated heart mitochondria show low permeability to most cations in the absence of a source of energy and of inducers of ion transport. Mitochondria are rapidly penetrated by NH4+ and to a lesser degree by Na+ under these conditions, however. In the presence of a source of energy, all cations tested appear to enter the mitochondrion by an energy-linked process. The extensive penetration of the mitochondrion by cations which results in osmotic swelling is dependent on the presence of a permeant anion. These studies suggest that the mitochondrial mechanism for cation uptake shows relatively little specificity as to cation. 2. 2. Gramicidin, an inducer of Na+ and K+ transport, increases the rate of swelling in isotonic Na+ or K+ acetate in the absence of an energy source. Addition of an uncoupler of oxidative phosphorylation lowers by two orders of magnitude the concentration of gramicidin which brings about this increased permeability. Gramicidin also releases the endogenous K+ of mitochondria suspended in K+-free media in the absence of a source of energy. These observations are compatible with the suggestion of a number of authors that gramicidin increases the permeability of the mitochondrial membrane to Na+ and K+. 3. 3. In contrast to gramicidin, Zn++ appears to have little effect on the permeability of the mitochondrion to cations in the absence of an energy source. However, once bound by an energy-linked reaction in the presence of phosphate, Zn++ causes an increase in passive permeability to K+, Na+, and Cl-. Mitochondria treated with Zn++ under these conditions remain impermeable to sucrose. © 1968.