Tissue adenosine content in active soleus and gracilis muscles of cats

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Abstract
Vascularly isolated cat soleus and gracilis muscles were stimulated to contract isometrically and were then frozen in situ. Adenosine, inosine and hypoxanthine (nucleosides) and lactate were measured in neutralized perchloric acid extracts of muscle. During contraction, nucleoside content increased in soleus muscle but changed little in gracilis muscle. Adenosine content did not correlate with vascular conductance or O2 consumption in either soleus or gracilis muscle. Adenosine content did correlate with lactate content in soleus but not gracilis muscle. The activity of AMP deaminase was highest in cat gracilis muscle and lowest in dog cardiac muscle. The activity of 5''-nucleotidase was lowest in cat gracilis muscle and highest in dog cardiac muscle. Cat soleus and dog gracilis muscles had intermediate activities of both enzymes. A role for adenosine in mediating prolonged active hyperemia in fast-twitch gracilis muscle of cats and such a role in slow-twitch soleus muscle of cats was not supported. Differences in the activities of AMP deaminase and 5''-nucleotidase provide a qualitative, biochemical explanation for apparent differences in net adenosine production among muscles composed of different fiber types and between skeletal and cardiac muscle.

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