Prostanoid receptor with a novel pharmacological profile in human erythroleukemia cells

Abstract

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 [Ca 2+], by different mechanisms. Iloprost (10 −9 to 10 −6 M) had no effect on basal [Ca 2+] i, but greatly potentiated the increase in [Ca 2+], 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 [Ca 2+] i in cells incubated in Ca 2+ -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 [Ca 2+] 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 [Ca 2+] i was not consistent with known IP, EP, DP, FP, or TP receptors. 11-Deoxy-16,16-dimethyl PGE 2 was the most potent of the analogs tested (EC 50 = 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.