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

¹Department of Radiology, ²School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania; ³Zentrum Physiology, Medizinische Hochschule Hannover, Hannover, Germany; and Departments of ⁴Physiology and ⁵Cell and Developmental Biology, University of Pennsylvania, Philadelphia, Pennsylvania

Submitted 22 December 2004 ; accepted in final form 29 March 2005

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-2K^b-ts a58) after 2–3.5 h without superfusion. In control studies, pH and phosphocreatine fell and P_i 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 P_i 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.

skeletal muscle cells; pH; NMR; acetazolamide; dimethylamiloride

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