Essential synergy between Ca2+ and guanine nucleotides in exocytotic secretion from permeabilized rat mast cells.

Abstract

Rat mast cells, pretreated with metabolic inhibitors and permeabilized by streptolysin-O, secrete histamine when provided with Ca2+ (buffered in the micromolar range) and nucleoside triphosphates. We have surveyed the ability of various exogenous nucleotides to support or inhibit secretion. The preferred rank order in support of secretion is ITP > XTP > GTP >> ATP. Pyrimidine nucleotides (UTP and CTP) are without effect. Nucleoside diphosphates included alongside Ca2+ plus ITP inhibit secretion in the order 2''-deoxyGDP > GDP > o-GDP > ADP .simeq. 2''deoxyADP .simeq. IDP. Secretion from the metabolically inhibited and permeabilized cells can also be induced by stable analogues of GTP (GTP-.gamma.-S > GppNHp > GppCH2p) which synergize with Ca2+ to trigger secretion in the absence of phosphorylating nucleotides. ATP enhances the effective affinity for Ca2+ and GTP analogues in the exocytotic process but does not alter the maximum extent of secretion. The results suggest that the presence of Ca2+ combined with activation of events controlled by a GTP regulatory protein provide a sufficient stimulus to exocytotic secretion from mast cells.