Abstract
To elucidate purine degradation in contracting skeletal muscle, we analyzed changes in concentrations of adenine nucleotides, IMP, inosine, and hypoxanthine in rat extensor digitorum longus (EDL, fast - twitch) and soleus (slow - twitch) muscles stimulated simultaneously via the sciatic nerve ( 5 Hz,25V,10min).
In EDL muscle, ATP concentration decreased progressively during stimulation. As ATP declined, not only IMP (from 0.09 ±0.01 to 1.72 ±0.32 μmol/g wet wt, mean ±SE), but inosine (from 0.016 ±0.003 to 0.164 ±0.019 μmol/g) and hypoxanthine (from 0.014 ±0.002 to 0.040 ±0.004 μmol/g) concentrations increased significantly. ADP and AMP concentrations remained almost unchanged. Adenylosuccinate increased very little during stimulation. Ten minutes after the end of stimulation (recovery period), IMP, inosine and hypoxanthine returned to their basal concentrations, but ATP was still lower than the basal value. In soleus muscle, there were no appreciable changes in these metabolite concentrations.
The present findings indicate 1) strenuous contraction caused greater purine catabolism in fast - twitch muscle than in slow - twitch muscle and 2) inosine formation was strongly correlated with the IMP accumulation. We concluded that a small quantity of intramuscular IMP, which is the degradation product of adenine nucleotide, could get out of the purine nucleotide cycle by being converted to nucleoside and oxypurine under the condition of strenuous contraction.
