Plasmalemmal H+ extruders in mammalian alveolar macrophages.
The distribution of plasmalemmal V-type H+-pumps (V-ATPase) among mammalian macrophages (mvarphi) is uncertain and, hence, the functional significance of mvarphi plasmalemmal V-ATPase is unclear. This study investigated the role of V-ATPase in the regulation of intracellular pH (pH(i)) by resident alveolar mvarphi from sheep, pigs, dogs and rabbits. The fluorescent probe 2',7'-biscarboxyethyl-5,6-carboxyfluorescein was used to monitor baseline pH(i) and the rate of pH(i) recovery (dpH(i)/dt) from intracellular acid-loads (NH(4)Cl prepulse). Baseline pH(i) was 7.1-7.2. In sheep, pig and dog studies, 10 microM bafilomycin A(1) (a selective V-ATPase inhibitor) caused a rapid fall in baseline pH(i) (0.15-0.20 units); baseline values were unaffected by 0.1 mM amiloride (a Na+ transport inhibitor). V-ATPase activity (bafilomycin-sensitive component of dpH(i)/dt) was solely responsible for pH(i) recovery from intracellular acid-loads at acid-loaded pH(i) values >6.8-6.9. Na+/H+ exchange (amiloride-sensitive component of dpH(i)/dt) was detected only at acid-loaded pH(i) values <6.8. The activity of both H+ extruders increased at lower pH(i) values, albeit the Na+/H+ exchanger was more pH-sensitive than was V-ATPase. In rabbit studies, 10 microM bafilomycin A(1) and 1 mM N-ethylmaleimide (a non-specific H+-pump inhibitor) produced similar falls in baseline mvarphi pH(i), but had significantly larger effects than did the selective V-ATPase inhibitor concanamycin A (<or=15 microM). The findings suggest that plasmalemmal V-ATPase activity plays a major role in pH(i) regulation by alveolar mvarphi of sheep, pigs, dogs and rabbits.
Heming
Thomas A
TA
Pulmonary and Critical Care Medicine, Department of Internal Medicine, University of Texas Health Science Center, Houston, TX 77225-0708, USA. Thomas.Heming@uth.tmc.edu
Bidani
Akhil
A
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D003208:Concanavalin A / Q000494:pharmacology; D004285:Dogs; D018942:Macrolides; D016676:Macrophages, Alveolar / Q000187:drug effects / Q000378:metabolism*; D011817:Rabbits; D012756:Sheep; D013552:Swine; D025262:Vacuolar Proton-Translocating ATPases / Q000378:metabolism*
D000900:Anti-Bacterial Agents; D018942:Macrolides; D003208:Concanavalin A; D000584:Amiloride; C040929:bafilomycin A1; D025262:Vacuolar Proton-Translocating ATPases