Ionic regulation of proton chemical (pH) and electrical gradients in lung lamellar bodies.
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.
Wadsworth
S J
SJ
Department of Pediatrics, Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
Spitzer
A R
AR
Chander
A
A
D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism; D002712:Chlorides / Q000494:pharmacology; D004594:Electrophysiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005456:Fluorescent Dyes; D006863:Hydrogen-Ion Concentration; D007477:Ions; D007555:Isoxazoles / Q000037:antagonists & inhibitors / Q000493:pharmacokinetics; D008168:Lung / Q000378:metabolism / Q000502:physiology*; D018942:Macrolides; D008297:Male; D011188:Potassium / Q000494:pharmacology; D011522:Protons; D011796:Quinacrine / Q000037:antagonists & inhibitors / Q000493:pharmacokinetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000494:pharmacology; D028021:Sodium-Potassium-Chloride Symporters
D000900:Anti-Bacterial Agents; D002352:Carrier Proteins; D002712:Chlorides; D004791:Enzyme Inhibitors; D005456:Fluorescent Dyes; D007477:Ions; D007555:Isoxazoles; D018942:Macrolides; D011522:Protons; D028021:Sodium-Potassium-Chloride Symporters; C013633:oxonol V; C040929:bafilomycin A1; D012964:Sodium; D011796:Quinacrine; D011188:Potassium