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Total CA activity in isolated perfused guinea pig lung by 18O-exchange method
S Nioka1, R P Henry, R E Forster
1Department of Physiology, School of Medicine, University of Pennsylvania, Philadelphia 19104-6085.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|November 1, 1988
Summary
This study measured carbonic anhydrase (CA) activity in guinea pig lungs. Results show lung CA significantly speeds up CO2 reactions, with only 10% accessible to pulmonary capillary plasma.
Area of Science:
- Biochemistry
- Physiology
- Enzymology
Background:
- Carbonic anhydrase (CA) is crucial for CO2 transport in the lungs.
- Understanding CA activity and accessibility is vital for respiratory physiology.
Purpose of the Study:
- To quantify carbonic anhydrase (CA) activity in isolated perfused guinea pig lungs.
- To determine the fraction of lung CA accessible to pulmonary capillary plasma.
Main Methods:
- Measured 18O exchange rate between alveolar CO2 and lung water.
- Utilized three sulfonamide CA inhibitors with varying membrane permeabilities (ethoxzolamide, acetazolamide, benzolamide).
- Assessed enzyme inhibition over time to infer accessibility to perfusate.
Main Results:
- Lung CA activity accelerates CO2 reactions by two orders of magnitude.
- Ethoxzolamide, acetazolamide, and benzolamide showed differential inhibition based on permeability.
- Approximately 10% of total lung CA activity was found to be available to pulmonary capillary plasma.
Conclusions:
- Lung CA activity is sufficient to catalyze rapid CO2 hydration/dehydration.
- The permeability of CA inhibitors correlates with their observed inhibition of lung enzyme activity.
- Pulmonary capillary plasma has access to a small fraction of the total lung CA.