Prostanoid receptor with a novel pharmacological profile in human erythroleukemia cells

The purpose of this study was to characterize the prostanoid receptors coupled to intracellular calcium in human erythroleukemia (HEL) cells, a cell line with platelet/megakaryocytic characteristics. Both prostaglandin E-1 (PGE(1)) and iloprost increased cyclic AMP (cAMP) in HEL cells, but modulated [Ca2+](i) by different mechanisms. Iloprost (10(-9) to 10(-6) M) had no effect on basal [Ca2+](i), but greatly potentiated the increase in [Ca2+](i) produced by thrombin. This effect was mimicked by cholera toxin and other G(s)-coupled receptors, and involved calcium influx since iloprost had no effect on [Ca2+](i) in cells incubated in Ca2+-free buffer. Furthermore, iloprost did not increase the generation of baseline or thrombin induced inositol phosphates at these concentrations. In contrast, PGE(1) (10(-7) to 10(-5) M), but not iloprost, increased basal [Ca2+](i) through a pertussis toxin-sensitive mechanism that involved stimulation of inositol phosphate generation and mobilization of intracellular calcium. The order of potencies of other prostaglandins that increased [Ca2+](i) was not consistent with known IF, EP, DP, FP, or TP receptors. 11-Deoxy-16, 16-dimethyl PGE(2) was the most potent of the analogs tested (EC50 = 28 nM). In summary, at least two prostaglandin receptors are functionally coupled to intracellular calcium in HEL cells: a putative IP receptor coupled to G(s) proteins that increases cAMP and enhances calcium influx, and a novel prostanoid receptor that evokes calcium mobilization through stimulation of phospholipase C by a pertussis toxin-sensitive pathway. (C) 1997 Elsevier Science Inc.