Calcium-pH crosstalks in rat mast cells: cytosolic alkalinization, but notintracellular calcium release, is a sufficient signal for degranulation

1 The aim of this work was to study the relationship between intracellular alkalinization, calcium fluxes and histamine release in rat mast cells. Int racellular alkalinization was induced by nigericin, a monovalent cation ion ophore, and by NH4Cl (ammonium chloride). Calcium cytosolic and intracellul ar pH were measured by fluorescence digital imaging using Fura-2-AM and BCE CF-AM. 2 In rat mast cells, nigericin and NH,CI induce a dose-dependent intracellu lar alkalinization, a dose-dependent increase in intracellular calcium leve ls by releasing calcium from intracellular pools, and an activation of capa citative calcium influx. 3 The increase in both intracellular calcium and pH activates exocytosis (h istamine release) in the absence of external calcium. Under the same condit ions, thapsigargin does not activate exocytosis, the main difference being that thapsigargin does not alkalinize the cytosol. 4 After alkalinization, histamine release is intracellular-calcium dependen t. With 2.5 mM EGTA and thapsigargin the cell response decreases by 62%. 5 The cytosolic alkalinization, in addition to the calcium increase it is e nough signal to elicit the exocytotic process in rat mast cells.