Acidification activity of human neutrophils. Tertiary granules as a site of ATP-dependent acidification

The acidification activity of human neutrophils, known to occur extracellularly and intraphagolysosomally, was studied in intact and in fractionated cells. The subcellular location of the acidification activity was investigated by rate zonal sedimentation of post-nuclear supernatants from resting cells on continuous sucrose gradients. The acidification measurements indicated a dominance of activity in gelatinase-rich tertiary granules. On the other hand, ATPase activities were located in plasma membrane and in the membranes of the cytoplasmic granules (specific, azurophilic, and tertiary). All of these activities were diminished by the inhibitors dicyclohexylcarbodiimide and diisothiocyanostilbene disulfonic acid; however, studies with other inhibitors, especially N-ethylmaleimide and duramycin, suggested ATPase enzymatic differences depending on location. The results taken together provide direct and strong indication of involvement of a proton pump ATPase in acidification inside neutrophils. Furthermore, the dominant location of acidification activity in tertiary granules that very readily degranulate presumably has significant implications for the importance of low pH in cidal events and the inflammatory process.