Effects of concanavalin A on Na+-dependent and Na+-independent mechanisms for H+ extrusion in alveolar macrophages

Abstract

Alveolar macrophages (mφ) possess two parallel mechanisms for plasmalemmal H+ extrusion: a V-type H+ pump (V-ATPase) and a Na+/H+ exchanger (NHE). To investigate the coordinated functioning of these H+ extruders for mφ intracellular pH (pH(i)) regulation, we investigated the effects of the plant lectin concanavalin A (ConA) on resident alveolar mφ from rabbits. ConA (l μM, 30-min pretreatment) activated the mφ for phagocytosis of opsonized Escherichia coli. ConA activation did not affect the baseline pH(i) of mφ or the initial rate of pH(i) recovery (dpH(i)/dt) from an intracellular acid load (acid-loaded pH(i) nadir = 6.9). However, the contributions of Na+-independent H+ transport (i.e. V-ATPase activity) and Na+-dependent H+ transport (i.e. NHE activity) to dpH(i)/dt were altered significantly. The lectin stimulated Na+/H+ exchange and inhibited V- ATPase activity. In control mφ, V-ATPase-mediated H+ extrusion was responsible for >80% of dpH(i)/dt. Conversely, in ConA-treated mφ, Na+/H+ exchange was responsible for ~65% of dpH(i)/dt, and V-ATPase activity was responsible for only 35% of dpH(i)/dt. These results underscore the complex mechanisms and signaling pathways that coordinate the activities of cellular acid-base transporters in mφ pH(i) regulation.