High K(m) of oxidative phosphorylation for ADP in skinned muscle fibers: where does it stem from?

Mitochondria in saponin-skinned cardiac fiber bundles were reported to have an order of magnitude lower apparent affinity to ADP than isolated mitochondria. Although ADP was measured outside the bundles, it was thought that the low affinity was not caused by diffusion gradients because of relatively short diffusion distances. Here we test the hypothesis that considerable ADP diffusion gradients exist and can be diminished by increasing the intrafiber ADP production rate.