Ion transport by heart and skeletal muscle mitochondria

¹ Department of Physiology, Yale University School of Medicine, New Haven, Connecticut

Isolated mitochondria from rat heart and skeletal muscle were able to maintain concentration gradients of sodium and potassium which were greater at low concentrations of either ion in the incubating medium than at high concentrations. Although the gradient of sodium was not significantly altered by addition of ATP and oxidizable substrate to the incubating medium, the mitochondria were able to accumulate increased amounts of potassium by these additions. When the mitochondria were aged by keeping them in suspension at 0–2° for 4 or 12 days, the potassium gradient was markedly decreased. 70–80% of the mitochondrial sodium exchanged with Na²² in the suspending medium in less than 1 minute and more than 90% of K⁴² had exchanged with mitochondrial potassium at the end of 5 minutes of incubation. Although addition of ATP and substrate to the suspending medium had no effect on the turnover of sodium, it appeared to render some of the potassium nonexchangeable. However by the end of 1 hour approximately 90% of the potassium had exchanged.

Note:
With the Technical Assistance of Fredrick W. Klein