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Department of Physiology, College of Medicine, Department of Biomedical Sciences, College of Veterinary Medicine, and Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri 65211
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 to 100 times normal, by employing an
isolated rat hindlimb preparation perfused at a high flow rate.
Incorporation of [3H]adenine or
[3H]hypoxanthine into the AdN pool was not meaningfully
influenced by tissue purine concentration over the range evaluated
(~0.10-1.6 µmol/g). Purine salvage rates were greater
(P < 0.05) for adenine than for hypoxanthine
(35-55 and 20-30
nmol · h
1 · g
1,
respectively) and moderately different (P < 0.05)
among fiber types. The low-oxidative fast-twitch white muscle section
exhibited relatively low rates of purine salvage that were ~65% of
rates in the high-oxidative fast-twitch red section of the
gastrocnemius. The soleus muscle, characterized by slow-twitch 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- to 6-fold, P < 0.001) and hypoxanthine (up to 6- to 8-fold, P < 0.001), depending on 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, inasmuch as delivery 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 over de novo synthesis of AdN. In the absence of ribose
supplementation, purine salvage rates are relatively low, especially
compared with the AdN pool size in skeletal muscle.
adenine; hypoxanthine; ribose
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