EFFECTS OF MYRISTATE PHORBOL ESTER ON V-ATPASE ACTIVITY AND NA+-H+ EXCHANGE IN ALVEOLAR MACROPHAGES

The roles of protein kinase C (PKC) in regulation of the plasmalemmal vacuolar-type H+-ATPase (V-ATPase) and Na+-H+ exchanger (NHE) of rabbit alveolar macrophages (m phi) were investigated using phorbol 12-myristate 13-acetate (PMA). At an extracellular pH (pH(o)) of 7.4 (nominal absence of CO2-HCO3-), PMA caused a dose-dependent increase in the rate of cellular H+ extrusion with little change in intracellular pH (pH(i)). PMA caused a prolonged cytosolic acidification at pH(o) less than or equal to 6.8. PMA-induced changes in pH(i) were sensitive to bafilomycin A(1), but were insensitive to amiloride. Studies of pH(i) recovery following intracellular acid challenge showed that both V-ATPase and the NHE were up-regulated by PMA. An inactive analog, 4 alpha-phorbol, had no detectable effects on pH; homeostasis. These data indicate that (a) PKC is involved in regulation of V-ATPase and the NHE of resident alveolar m phi and (b) V-ATPase is the predominant mechanism for pH(i) homeostasis in unstimulated and PMA-activated m phi.