Effects of Na+/H+ antiport and intracellular pH in the regulation of HL-60 cell apoptosis.

The roles of Na+/H+ antiport and intracellular pH in apoptosis of HL-60 cells were investigated here. We found that dimethyl amiloride, a specific Na+/H+ antiport inhibitor, induced intracellular acidification but not apoptosis; while sodium ionophore, monensin caused intracellular alkalinization as well as apoptosis in HL-60 cells. Br-A23187 and thapsigargin could induce a various degree of intracellular alkalinization through the stimulation of Na+/H+ antiport. Dimethyl amiloride blocked the intracellular alkalinization and inhibited apoptosis induced by Br-A23187 and thapsigargin. PMA also stimulated Na+/H+ antiport and induced intracellular alkalinization which was completely blocked by dimethyl amiloride and partially attenuated by PKC inhibitors. PMA could inhibit apoptosis in HL-60 cells. PMA-induced suppression of apoptosis was, however, not interfered by dimethyl amiloride, but could be abolished by PKC inhibitors. These results indicate that pHi alkalinization and/or the stimulation of Na+/H+ antiport, instead of intracellular acidification, are contributory to the induction of apoptosis. PMA-induced inhibition of apoptosis is not necessarily associated with intracellular alkalinization, but primarily due to activation of PKC. We suggest that stimulation of Na+/H+ antiport and pHi alkalinization act as facilitating factors in the induction of apoptosis.