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Am J Physiol Lung Cell Mol Physiol 273: L427-L436, 1997;
1040-0605/97 $5.00
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AJP - Lung Cellular and Molecular Physiology, Vol 273, Issue 2 427-L436, Copyright © 1997 by American Physiological Society

ARTICLES

Ionic regulation of proton chemical (pH) and electrical gradients in lung lamellar bodies

S. J. Wadsworth, A. R. Spitzer and A. Chander
Department of Pediatrics, Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.

This study investigated the pH (chemical) and electrical gradients in lamellar bodies, the acidic surfactant-secreting organelles of lung epithelial type II cells, by following the uptake of a weak fluorescent base, quinacrine, and a membrane potential-sensitive dye, bis-(3-phenyl-5-oxoisoxazol-4-yl)pentamethine oxonol (oxonol V). In isolated lung lamellar bodies, the ATP-dependent uptake of both agents could be inhibited by bafilomycin A1, a reportedly specific inhibitor of vacuolar-type H(+)-ATPase (V-ATPase) and could be dissipated by a protonophore, carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone, suggesting that the V-ATPase generates an electropositive interior. A closely linked uptake of Cl- neutralizes the positive electrical potential and increases the proton pump activity. The uptake of quinacrine, but not oxonol V, was decreased by Na+. This effect of Na+ could be prevented by dimethylamiloride, suggesting the presence of electroneutral Na+/H+ exchanger in lamellar body membranes. The initial rates of quinacrine and oxonol V uptake were increased by bumetanide, but only in the presence of Na+, K+, and Cl-, suggesting that the lamellar bodies also contain an outwardly directed electroneutral Na(+)-K(+)-2Cl- cotransporter. Thus three ion transporters, H(+)-translocating V-ATPase, Na+/H+ exchanger, and Na(+)-K(+)-2Cl- cotransporter, appear to determine the chemical and electrical gradients across the lamellar body membrane.


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