Receptor-mediated increases in cytosolic Ca2+ in the human erythroleukaemia cell line involve pertussis toxin-sensitive and -insensitive pathways.
The pluripotent human erythroleukaemia cell line, HEL, possesses erythrocytic, megakaryocytic and macrophage-like properties. With respect to signal transduction, HEL cells have been used as a model system for platelets, but little attention has been paid to their phagocytic properties. We studied the effects of various receptor agonists on the intracellular free Ca2+ concentration ([Ca2+]i) in HEL cells. Thrombin, platelet-activating factor (PAF), ATP, UTP, prostaglandins E1 and E2 (PGE1 and PGE2), the PGE2 analogue sulprostone and the stable PGI2 analogues iloprost and cicaprost increased [Ca2+]i. ADP was less effective than ATP, and UDP was unable to increase [Ca2+]i. The increases in [Ca2+]i induced by thrombin, PAF, ATP, UTP, iloprost and cicaprost were pertussis toxin-insensitive, whereas the increases induced by PGE2 and sulprostone were completely inhibited by the toxin. The increase in [Ca2+]i induced by PGE1 was partially inhibited by pertussis toxin. PGE2 did not desensitize the increase in [Ca2+]i induced by iloprost, and vice versa. PGE1 desensitized the response to PGE2 and iloprost but not vice versa. Adrenaline potentiated the iloprost- but not the PGE2-induced rise in [Ca2+]i. The phorbol ester phorbol 12-myristate 13-acetate completely blocked the rise in [Ca2+]i induced by ATP and PGE1, whereas the increases induced by thrombin and PAF were only partially inhibited. Agonists increased [Ca2+]i through release from internal stores and sustained Ca2+ influx. Thrombin stimulated Mn2+ influx, which was blocked by Ni2+. Diltiazem, isradipine, gramicidin and 1-(beta-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenethyl)-1H-imidazole hydrochloride (SK&F 96365) did not affect agonist-induced rises in [Ca2+]i. HEL cells contained substantial amounts of beta-glucuronidase which, however, could not be released, and they did not aggregate or generate superoxide. Our data suggest that: (1) HEL cells possess nucleotide receptors with properties similar to those of phagocytes; (2) they possess receptors for PGE2 and PGI2, and PGE1 is an agonist at both receptors; (3) agonist-induced increases in [Ca2+]i are mediated through pertussis toxin-sensitive as well as -insensitive signal transduction pathways; and (4) agonists increase [Ca2+]i by mobilization from internal stores and influx from the extracellular space through cation channels with properties similar to those of phagocytes and platelets.
Schwaner
I
I
Institut für Pharmakologie, Freie Universität Berlin, Germany.
Seifert
R
R
Schultz
G
G
D000255:Adenosine Triphosphate / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism*; D011464:Epoprostenol / Q000378:metabolism; D006801:Humans; D004915:Leukemia, Erythroblastic, Acute; D037342:Pertussis Toxin; D010972:Platelet Activating Factor / Q000378:metabolism; D011458:Prostaglandins E / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000378:metabolism; D015398:Signal Transduction; D013917:Thrombin / Q000378:metabolism; D014407:Tumor Cells, Cultured; D014544:Uridine Triphosphate / Q000378:metabolism; D010566:Virulence Factors, Bordetella / Q000494:pharmacology*
D010972:Platelet Activating Factor; D011458:Prostaglandins E; D011956:Receptors, Cell Surface; D010566:Virulence Factors, Bordetella; D000255:Adenosine Triphosphate; D011464:Epoprostenol; D037342:Pertussis Toxin; D013917:Thrombin; D002118:Calcium; D014544:Uridine Triphosphate