[Localization of adenylate cyclase in red and white skeletal muscle: a cytochemical study]

An attempt was made to demonstrate adenylate cyclase (ATP pyrophosphate-lyase (cyclizing) EC 4.6.1.1) activity in white and red skeletal muscle (M. psoas and M. soleus) of guinea pigs cytochemically by the lead precipitation technique. 5'-Adenylylimidodiphosphate served as substrate. The free lead ion concentration in the incubation medium was kept below the value that is toxic to the enzyme. An electron dense reaction product, presumably lead imidodiphosphate, was deposited in the soleus muscle (red muscle fibers) at all parts of the plasma membrane and in the psoas muscle (white muscle fibers) chiefly at the membranes of the sarcoplasmic reticulum. The reaction at the latter site was enhanced by adrenaline; the enhancement was prevented by propranolol. These findings are in good agreement with results that have been obtained by other authors in experiments on subcellular fractions of the two types of muscle.