Action of weak bases on phagosomes of cultured macrophages. Suppression by ammonium ions of an early increase in phagosomal pH

Abstract A transient increase in pH of newly-formed phagosomes in cultured macrophages, which occurs immediately after phagocytosis, is suppressed after pre-exposure of the cells to ammonium ions (as NH 4 Cl), but not to chloroquine. The increase in intravacuolar pH proceeds normally after removal of ammonium ions from the extracellular medium. This difference between the two weak bases contrasts with their similarity in many cellular effects. Our observations emphasize the significance of the earliest events accompanying phagocytosis.