Release of serotonin from RBL-2H3 cells by the Escherichia coli peptide toxin STb.

Heat-stable enterotoxin b (STb) of Escherichia coli is a 48-amino acid basic, disulfide-bonded peptide that causes intestinal secretion in experimental animal models. Recent evidence suggests that the in vivo mechanism of STb action involves release of 5-hydroxytryptamine (5-HT) and production of prostaglandin E2 (PGE2). Here we show STb-mediated release of 5-HT from rat basophilic leukemic cells (RBL-2H3), a mast cell line model used extensively to study 5-HT release. Increasing concentrations of biologically active STb resulted in a dose-dependent release of 5-HT from RBL-2H3 cells. In contrast to these results, reduced and alkylated STb had no effect on 5-HT release. Release of 5-HT from RBL-2H3 cells was independent of extracellular calcium ions and did not involve changes in the intracellular concentration of free Ca2+. In addition, pertussis toxin treatment completely blocked 5-HT release, indicating a role for a pertussis toxin-sensitive G-protein in the mechanism of 5-HT release from this cell type.