Velocity of CO2 exchange in muscle and liver.

Abstract

Until about ten years ago it had been generally believed (82, 108) that carbonic anhydrase is not present in muscle tissue. Although it is acknowl­ edged that exercising skeletal muscle is organ with one of the highest rates of CO2 production and tissue Pco2, it was questioned whether fast kinetics of the CO2 reactions would be useful for the elimination of CO2• Roughton (108) argued that carbonic anhydrase in such a tissue would be an enemy to the organism rather than a friend because it would favour the conversion of CO2, which diffuses quickly and permeates cell membranes easily (41), to HC03 -, a form of CO2 whose diffusivity is somewhat smaller and whose permeability across the muscle cell membrane is extremely low (131). During the last decade not only have several forms of carbonic anhydrase been found in skeletal muscle, but it is also clear that the presence of carbonic anhydrase is in fact useful for the elimination of CO2 from muscle tissue. It has been shown by Gros et al (43) that very little carbamate is formed by the muscle proteins. The hydration-dehydration reaction thus appears to be the only reaction of CO2 that is important in muscle. This review will therefore entirely concentrate on the enzyme that determines its velocity, namely carbonic anhydrase.