Effect of carbonic anhydrase III inhibition on substrate utilization and fatigue in rat soleus

Carbonic anhydrase III (CA III; EC 4.2.1.1) is the most abundant cytosolic enzyme in type I skeletal muscle fibers. We have previously shown that inhibiting the CA III activity of type I muscle can influence fatigability. Our goal was to test the hypothesis that the influence on fatigability of CA III inhibition is linked to an increased utilization of carbohydrates. Rat soleus muscles were incubated in vitro in a physiological solution with or without CA inhibitor (methazolamide, 1 mM) and submitted to a fatigue protocol. When the bathing solution contained glucose, the muscles incubated with methazolamide maintained a higher level of tension production than control muscles for the first 55-60 min of the test compared with 35-40 min when glucose was not added. Measurement of muscle glycogen content revealed that muscles incubated with CA inhibitor were utilizing their glycogen at a higher rate than control muscles over the first 45 min of the fatigue protocol. When glycolysis was inhibited with sodium iodoacetate, fatigability was not influenced by the addition of a CA inhibitor. These results further support the existence of a link between CA III activity and energy metabolism in type I skeletal muscle fibers.