Purine salvage to adenine nucleotides in different skeletal muscle fiber types

Rates of purine salvage of adenine and hypoxanthine into the adenine nucleo tide (AdN) pool of the different skeletal muscle phenotype sections of the rat were measured using an isolated perfused hindlimb preparation. Tissue a denine and hypoxanthine concentrations and specific activities were control led over a broad range of purine concentrations, ranging from 3 to 100 time s normal, by employing an isolated rat hindlimb preparation perfused at a h igh flow rate. Incorporation of [H-3] adenine or [H-3] hypoxanthine into th e AdN pool was not meaningfully influenced by tissue purine concentration o ver the range evaluated (similar to0.10-1.6 mmol/g). Purine salvage rates w ere greater (P < 0.05) for adenine than for hypoxanthine (35-55 and 20-30 n mol.h(-1).g(-1), respectively) and moderately different (P < 0.05) among fi ber types. The low-oxidative fast-twitch white muscle section exhibited rel atively low rates of purine salvage that were similar to 65% of rates in th e high-oxidative fast-twitch red section of the gastrocnemius. The soleus m uscle, characterized by slow-twitch red fibers, exhibited a high rate of ad enine salvage but a low rate of hypoxanthine salvage. Addition of ribose to the perfusion medium increased salvage of adenine (up to 3- to 6-fold, P < 0.001) and hypoxanthine (up to 6- to 8-fold, P < 0.001), depending on fibe r type, over a range of concentrations up to 10 mM. This is consistent with tissue 5-phosphoribosyl-1-pyrophosphate being rate limiting for purine sal vage. Purine salvage is favored over de novo synthesis, inasmuch as deliver y of adenine to the muscle decreased (P < 0.005) de novo synthesis of AdN. Providing ribose did not alter this preference of purine salvage pathway ov er de novo synthesis of AdN. In the absence of ribose supplementation, puri ne salvage rates are relatively low, especially compared with the AdN pool size in skeletal muscle.