Journal of Applied Physiology, Vol 49, Issue 4 589-600, Copyright © 1980 by American Physiological Society
Carbonic anhydrase activity of rabbit lungs
R. M. Effros, L. Shapiro and P. Silverman
Pulmonary carbonic anhydrase (CA) activity was studied in rabbit lungs
perfused with solutions containing no CA. Measurements were made of the
amount of 14CO2 appearing in the expired gas following injections of
H14CO3(-), 14CO2, or a 20:1 mixture of each into the pulmonary artery. The
fraction of the injected label in the expired gas was only 17% greater for
14CO2 than for the mixture, suggesting that equilibration between H14CO3(-)
and 14CO2 was nearly complete during the capillary transit time. Inhibition
of pulmonary CA decreased excretion of H14CO3(-) and the mixture by 40 and
49% and increased the excretion of 14CO2 by 96%. Addition of CA to the
perfusate had no effect. Thus, CO2 exchange is not significantly limited by
pulmonary CA if inhibitors are absent. Tissue binding of [3H]acetazolamide
injected into the pulmonary artery was diminished by 50% when acetazolamide
concentrations reached 0.13 x 10(-6) M. Each liter of extravascular lung
water contained 1.25 x 10(-6) mol of receptors for acetazolamide that were
accessible to plasma during a single circulation. Binding of
[3H]acetazolamide was also observed in lungs of anesthetized rabbits,
suggesting that pulmonary CA is accessible to plasma in vivo as well as in
situ.
