DIFFERENTIAL RELEASE OF HISTAMINE AND PROSTAGLANDIN D-2 IN RAT PERITONEAL MAST-CELLS - ROLES OF CYTOSOLIC CALCIUM AND PROTEIN-TYROSINE KINASES

We studied how the release of histamine and prostaglandin D-2 (PGD(2)) were connected in stimulated rat peritoneal mast cells, and to what extent these processes were controlled by the cytosolic Ca2+ concentration, [Ca2+](i), and protein tyrosine kinases. In the presence of 1 mM CaCl2, the G-protein activating compound 48/80 (10 mu g/ml) evoked a transient rise in [Ca2+](i) and a relatively high secretion of histamine, but only a low release of PGD(2). In contrast, 5 mu M thapsigargin (an inhibitor of endomembrane Ca2+-ATPases) and 5 mu M ionomycin evoked high and prolonged rises in [Ca2+](i), and stimulated the cells to release relatively small amounts of histamine and high amounts of PGD(2). Stimulation of the cells with CaCl2 and 10 mu M ATP(4-) gave only minor quantities of histamine and PGD(2), despite of the micromolar level of [Ca2+](i) reached. When CaCl2 was replaced by EGTA, rises in [Ca2+](i) as well as release of histamine and PGD(2) were reduced with each agonist, but the preference of agonists to release more histamine or PGD(2) remained unchanged. In mast cells with depleted Ca2+ stores, the addition of CaCl2 stimulated the store-regulated Ca2+ entry resulting in a prolonged rise in [Ca2+](i). However, simultaneous addition of compound 48/80 and CaCl2 was required for release of histamine and PGD,. In cells with full stores, PGD(2) release evoked by compound 48/80 was greatly reduced by genistein and methyl-2,5-dihydroxycinnamate, two structurally unrelated inhibitors of protein tyrosine kinases, whereas histamine secretion was not influenced by these inhibitors. Similarly, with thapsigargin or ionomycin as agonist, PGD(2) release was more sensitive to the tyrosine kinase inhibitors than histamine secretion. We conclude that in activated rat peritoneal mast cells: (i) the influx of extracellular Ca2+ potentiates agonist-evoked rises in [Ca2+](i) as well as histamine secretion and PGD, release (ii) the amplitude of the [Ca2+](i) rise does not determine the preferential effect of agonists to release more histamine or more PGD(2); ()the relatively high PGD(2) release evoked by thapsigargin and ionomycin is probably due to (iii) their potency to evoke a prolonged rise in [Ca2+](i) and to activate protein tyrosine kinases.