Mutual relationship among cytosolic pH, Na+ and Ca2+ ions in the degranulation of rat leukemic basophils.

Reagents which affect the cytosolic concentrations of protons and sodium ions markedly affect the degranulation process of mast cells. The proton-sodium exchanging ionophore, monensin, is found to cause noncytolytic dose dependent serotonin release from the rat leukemic basophils (line RBL-2H3). Its half maximal dose of ca. 2 microM leads to secretion of ca. 20% of these cells' serotonin content. Monensin induced serotonin secretion increases with external pH and decreases upon lowering external sodium ion concentrations, yet is independent on external calcium. Monitoring cytosolic pH and free Ca2+ concentrations with BCECF and quin2, respectively, shows that a rise in pHi and [Ca2+]i is caused by the ionophore. Amiloride, the blocker of cellular Na+/H+ antiporter, is found to be an effective inhibitor of antigen or monensin induced serotonin release. However, it does not by itself cause secretion. In contrast, ouabain, which inhibits the cellular Na+/K+ ATPase, does induce secretion. Cellular levels of pH, Na+ and Ca2+ ions are evidently linked and involve a manifold of activities. Though exchanging protons for sodium seems to be effective in causing mediator release, the present results do not provide sufficient support for proton/sodium ions having a second messenger role in the immunologically induced mediator release.