Effects of myristate phorbol ester on V‐ATPase activity and Na + ‐H + exchange in alveolar macrophages

The roles of protein kinase G (PKC) in regulation of the plasmalemmal vacuolar‐type H + ‐ATPase (V‐ATPase) and Na + ‐H + exchanger (NHE) of rabbit alveolar macro phages (m φ) were investigated using phorbol 12‐myristate 13‐acetate (PMA). At an extracellular pH (pH o ) of 7.4 (nominal absence of CO2‐HCO ‐ 3 ), 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 < 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 α ‐phorbol, had no detectable effects on pH i homeostasis. These data indicate that (a) PKC is involved in regulation of V‐ATPase and the NHE of resident alveolar m φ and (b) V‐ATPase is the predominant mechanism for pH i homeostasis in unstimulated and PMA‐activated m φ. J. Leukoc. Biol. 57: 600–608; 1995.