The role of carbonic anhydrase in the recovery of skeletal muscle from anoxia

To investigate the role of carbonic anhydrase in the recovery of skeletal muscle from anoxia, pH and cell phosphates were measured by 31P-nuclear magnetic resonance in superfused newborn rabbit myotubes and cultured mouse soleus cells (H-2Kb-ts a58) after ∼2–3.5 h without superfusion. In control studies, pH and phosphocreatine fell and Pi rose during anoxia and recovered within <10 min after reperfusion began. A carbonic anhydrase inhibitor, acetazolamide, and dimethylamiloride, an inhibitor of the Na+/H+ antiporter NHE1, delayed the recoveries of pH, phosphocreatine, and Pi for >10 min, but the rate of recovery, once initiated, was unchanged. In the presence of the inhibitors, after reperfusion started, the pH did not rise immediately, despite a large inwardly directed HCO3− gradient, suggesting that HCO3− movement was unimportant in acid elimination. Lactate, measured by its methyl protons, rose during anoxia and did not fall after 1 h of reperfusion and could not have eliminated protons by cotransport. We conclude that NHE1 is the major exporter of protons by skeletal muscle in recovery from a period of anoxia and that it is essential for functioning carbonic anhydrase to be attached to NHE1 to activate it. The mechanism of late recovery of pH could be the mobilization of another proton transporter or removal of the inhibition of the Na+/H+ antiporter. Inhibition of carbonic anhydrase in skeletal muscle retards acid removal and modifies muscle metabolism significantly after anoxia.