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Evidence for active H+ secretion by rat alveolar epithelial cells
R L Lubman1, S I Danto, E D Crandall
1Will Rogers Institute Pulmonary Research Program, Cornell University Medical College, New York, New York 10021.
The American Journal of Physiology
|December 1, 1989
Summary
Researchers identified a proton-pump (H(+)-ATPase) in rat lung cells, crucial for regulating intracellular pH and lung fluid balance. This finding advances our understanding of alveolar cell function.
Area of Science:
- Cell Biology
- Respiratory Physiology
- Biochemistry
Background:
- Alveolar pneumocytes play a vital role in lung function.
- Regulation of intracellular pH (pHi) is critical for cellular homeostasis.
- The role of plasma membrane proton pumps in alveolar cells was previously unclear.
Purpose of the Study:
- To identify and characterize a plasma membrane proton-translocating adenosinetriphosphatase (H(+)-ATPase) in rat alveolar pneumocytes.
- To investigate the contribution of this H(+)-ATPase to intracellular pH regulation and recovery from acidification.
- To determine the interplay between H(+)-ATPase and Na(+)-H+ antiport in maintaining steady-state pHi.
Main Methods:
- Primary culture of rat alveolar pneumocytes.
- Measurement of intracellular pH (pHi) using the fluorescent probe 2',7'-biscarboxyethyl-5,6-carboxyfluorescein.
- Acute intracellular acidification via NH3 prepulse.
- Assay of pHi recovery in the presence of amiloride (Na(+)-H+ antiport inhibitor) and N-ethylmaleimide (NEM, H(+)-ATPase inhibitor).
- Experiments conducted in Na(+)-containing/free buffers and with metabolic inhibition (KCN).
Main Results:
- A plasma membrane H(+)-ATPase was identified in rat alveolar pneumocytes.
- Inhibition of H(+)-ATPase (using NEM) significantly reduced pHi recovery from acidification.
- Combined inhibition of H(+)-ATPase and Na(+)-H+ antiport (using NEM and amiloride) almost completely abolished pHi recovery.
- Steady-state pHi was maintained by an active H(+)-ATPase and inactive Na(+)-H+ antiport at physiological pH.
- The H(+)-ATPase activity was dependent on Na+ and inhibited by KCN.
Conclusions:
- Rat alveolar epithelial cells possess a functional plasma membrane H(+)-ATPase.
- This H(+)-ATPase plays a significant role in regulating steady-state pHi and recovery from intracellular acidification.
- The identified H(+)-ATPase may contribute to modulating extracellular alveolar fluid pH, impacting lung physiology.