Adenine nucleotide degradation in slow-twitch red muscle

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Abstract
The catabolism of adenine nucleotides (AdN) in rat soleus muscle (predominantly slow twitch) is very different from that in fast-twitch muscle. AMP deaminase is highly inhibited during brief (3 min) intense (120 tetani/min) in situ stimulation, resulting in little inosine 5'-monophosphate (IMP) accumulation (0.21 mumol/g). Even with ligation of the femoral artery during the same brief intense contraction conditions there is surprisingly little increase in IMP (0.37 mumol/g), although AdN depletion is evident (-1.30 mumol/g). We have tested the hypothesis that accumulation of purine nucleosides and bases accounts for the AdN depletion by measuring purine degradation products using high-performance liquid chromatography. There was no stoichiometric accumulation of purine degradation products to account for the observed AdN depletion even though metabolite recovery was essentially quantitative. We hypothesis that under these conditions AdN are converted to a form different from purine nucleoside and base degradation products. In contrast to the inhibition of AMP deamination seen during brief ischemia, slow-twitch muscle depletes a substantial fraction (28%) of muscle AdN (1.75 mumol/g) that can be accounted for stoichiometrically as purine degradation products during an extended 10-min ischemic period of mild (12 tetani/min) contraction conditions. IMP accumulation (1 mumol/g) is most prominent with inosine, accounting for 23% (0.4 mumol/g) of the depleted AdN, showing that slow-twitch red muscle is capable of both AMP deamination and the subsequent production of purine nucleosides during an extended period of ischemic contractions. The present results indicate that AdN metabolism in the soleus muscle is complex, yielding expected degradation products or a loss of total purines, depending on contraction conditions.(ABSTRACT TRUNCATED AT 250 WORDS)