Electrically stimulated isolated extensor digitorum longus (EDL) muscles were used to assess the effect of probenecid on force development. For this, 8-wk-old OF1 male mice were anesthetized by isoflurane inhalation and killed by cervical dislocation, and EDL muscles were removed. Force measurements were performed using the 1205A Isolated Muscle System from Aurora Scientific. The EDL muscle was mounted in the experimental chamber in the presence of air-bubbled Ringer solution (see Solutions) maintained at 25°C. The muscle was stretched to the optimum length for the production of maximum isometric twitch force triggered by a supra-maximum 0.2-ms-long electrical stimulation. From this time point, the muscle was repeatedly stimulated by a series of five such electrical stimulations applied at 0.1 Hz, every 5 min, throughout the experiment. Force measurements were performed in response to 60 Hz supramaximum tetanic trains of stimulations of 0.5 s total duration, applied every 15 min. Following the first tetanic response, the Ringer solution was exchanged for the DMSO-containing Ringer with or without probenecid. Force values were normalized by the weight of the muscle.