Action of gramicidin on mitochondria: II. Ion-dependent mitochondrial volume changes energized by substrate oxidation

Abstract

Respiration-energized mitochondrial volume changes which are dependent on the presence of gramicidin and ions share the following features in common with the adenosine 5′-triphosphate (ATP)-energized process: (a) Under the conditions used Na + is less effective than Li + or K + in satisfying the permeant cation requirements and inhibits volume changes in the presence of K + but not in the presence of Li +; (b) addition of 2,4-dinitrophenol, phthalate, or hydrazine results in inhibition of mitochondrial volume changes. The following significant differences between respiration-and ATP-energized mitochondrial volume changes were found: (a) Sulfate and l-malate, which readily satisfy permeant anion requirements for ATP-energized volume changes, lead only to slow sustained swelling when the process is energized by respiration; (b) Addition of p-hydroxymercuribenzoate (PHMB), which induces damped harmonic oscillatory mitochondrial volume changes in the ATP-energized system, inhibits the respiration energized process. Comparison of the ATP- and respiration-energized systems leads us to propose that both processes share in common portions of the energy conservation pathway. The differential effects of PHMB on the ATP- and respiration-energized process may be based on the reaction of PHMB with a sulfhydryl group which is essential for the respiration-energized process but not required for the ATP-energized process.