Mode of action of prilocaine on sarcoplasmic reticulum in skinned skeletal muscle fibers.

Single fibers were isolated from the semitendinosus muscle of a frog and the skinned fibers were prepared by the removal of the sarcolemma. In the range of several millimolar concentrations, prilocaine caused a contracture of the single fibers in both polarized and depolarized states. It also induced Ca++ release from the sarcoplasmic reticulum and depressed Ca++ uptake by the sarcoplasmic reticulum. Prilocaine increased the release of Ca++ with increasing concentration, but, unlike caffeine, prilocaine could not enhance the Ca++-induced Ca++ release mechanism of the sarcoplasmic reticulum. Like a depolarization-induced Ca++ release, the prilocaine-induced Ca++ release was not inhibited by Mg++, whereas it was inhibited by sucrose. The Ca++ release induced with prilocaine occurred only immediately after the application; thereafter the Ca++ release mechanism seemed to be inactivated by the prolonged presence of the drug. A similar inactivation in the mechanism of prilocaine-induced Ca++ release also occurred when the extent of depolarization of the sarcoplasmic reticulum membrane increased. These results suggest that the mode of action of prilocaine on the sarcoplasmic reticulum could be a depolarization-like action.