Mitochondrial oxidative phosphorylation in saponin-skinned human muscle fibers is stimulated by caffeine.

The addition of 15 mM caffeine to saponin-skinned human muscle fibers from M. vastus lateralis caused in the presence of 2 mM ATP an approx. 2-fold stimulation of respiration with glutamate+malate. This effect can be abolished by either the addition of the Ca2+ chelator EGTA, the inhibitor of Ca2+ transport Ruthenium red and the inhibitor of the myosin ATPase vanadate. The caffeine concentration dependency of respiration of fibers coincided with the caffeine-caused stimulation of myosin ATPase activity. The activation of oxidative phosphorylation in saponin-skinned human muscle fibers by caffeine can be explained by a stimulation of myosin ATPase caused by Ca2+ release from sarcoplasmic reticulum.