Jeffrey J. Brault and Ronald L. Terjung.
Physiology. College of Medicine Biomedical Sciences, College of Veterinary Medicine, and Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO 65211
The rates of purine salvage of adenine and hypoxanthine into the adenine nucleotide (AdN) pool of the different skeletal muscle phenotype sections of the rat were measured using an isolated perfused hindlimb preparation. Tissue adenine and hypoxanthine concentrations and specific activities were controlled over a broad range of purine concentrations, ranging from 3-100 fold normal, by employing an isolated rat hindlimb preparation perfused at a high flow rate. Incorporation of H-adenine or 3H-hypoxanthine into the AdN pool was not meaningfully influenced by tissue purine concentration over the range evaluated (-0.10 to 1.6 µmol/g). Purine salvage rates were greater (p<0.05) for adenine (35-55 nmol/h/g), compared to hypoxanthine (20-30 nmol/h/g), and moderately different (p<0.05) among fiber types. The low oxidative fasttwitch white muscle section exhibited relatively low rates of purine salvage that were -65% of the rates in the high-oxidative fast twitch red section of the gastrocnemius. The soleus muscle, characterized by slowtwitch red fibers, exhibited a high rate of adenine salvage, but a low rate of hypoxanthine salvage. Addition of ribose to the perfusion medium increased salvage of adenine (up to 3-6 fold; p<0.00 1) and hypoxanthine (up to 6-8 fold; p<0.001), depending upon the fiber type, over a range of concentrations up to 10 mM. This is consistent with tissue 5-phosphoribosyl-1-pyrophosphate being rate limiting for purine salvage. Purine salvage is favored over de novo synthesis, as delivery of adenine to the muscle decreased (p<O.OOS) de novo synthesis of AdN. Providing ribose did not alter this preference of purine salvage pathway over de novo synthesis of adenine nucleotides. In the absence of ribose supplementation purine salvage rates are relatively low, especially compared the AdN pool size in skeletal muscle.