title: The role of cytosolic free calcium in the generation of inositol 1,4,5-trisphosphate and inositol 1,3,4-trisphosphate in HL-60 cells. Differential effects of chemotactic peptide receptor stimulation at distinct Ca2+ levels.
abstract: The generation of the two inositol trisphosphate (IP3) isomers, 1,4,5-IP3 and 1,3,4-IP3, and its relation to changes in the cytosolic free calcium concentration, [Ca2+]i, in response to the chemotactic peptide fMet-Leu-Phe was studied in the human promyelocytic cell line HL-60, induced to differentiate with dimethyl sulfoxide. Stimulation by fMet-Leu-Phe within seconds transiently elevates 1,4,5-IP3 to peak values averaging 8-fold basal levels, and leads to a concomitant rise in [Ca2+]i and to degranulation. These responses are followed by a slower and more sustained rise in 1,3,4-IP3. Alterations in [Ca2+]i modulate differentially the generation of the two IP3 isomers. At [Ca2+]i lower than 30 nM, no IP3 is generated upon fMet-Leu-Phe stimulation. Working at normal resting [Ca2+]i, but preventing the fMet-Leu-Phe induced transient rise in [Ca2+]i (by prior depletion of intracellular Ca2+ stores and working in calcium-free medium) the fMet-Leu-Phe stimulation of 1,3,4-IP3 levels is attenuated, whereas the response of 1,4,5-IP3 is not significantly altered. Maintained elevation of [Ca2+]i to micromolar levels with the Ca2+ ionophore ionomycin generates enhanced 1,3,4-IP3 levels in the absence of fMet-Leu-Phe, whereas the fMet-Leu-Phe stimulation of 1,4,5-IP3 generation is markedly inhibited. Pertussis toxin selectively abolishes the fMet-Leu-Phe-induced IP3 production, whereas ionomycin stimulation of 1,3,4-IP3 generation is unaffected. These findings indicate that in intact cells: receptor-triggered phosphatidylinositol bisphosphate phosphodiesterase activation has a minimal Ca2+ requirement, but does not depend on a previous or concomitant rise in [Ca2+]i; Ca2+ elevations above micromolar levels decrease the fMet-Leu-Phe-induced generation of 1,4,5-IP3; and 1,3,4-IP3 generation is not directly linked to receptor activation and appears to result both from increased [Ca2+]i and 1,4,5-IP3 levels.
mesh_terms: D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D002851:Chromatography, High Pressure Liquid; D003600:Cytosol / Q000378:metabolism; D004987:Ethers / Q000494:pharmacology; D005089:Exocytosis / Q000187:drug effects; D006596:Hexosaminidases / Q000378:metabolism; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate; D007295:Inositol Phosphates / Q000096:biosynthesis*; D015759:Ionomycin; D015470:Leukemia, Myeloid, Acute / Q000378:metabolism*; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D037342:Pertussis Toxin; D044042:Receptors, Formyl Peptide; D011971:Receptors, Immunologic / Q000378:metabolism*; D013403:Sugar Phosphates / Q000096:biosynthesis*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D004987:Ethers; D007295:Inositol Phosphates; D044042:Receptors, Formyl Peptide; D011971:Receptors, Immunologic; D013403:Sugar Phosphates; D010566:Virulence Factors, Bordetella; D015759:Ionomycin; D009240:N-Formylmethionine Leucyl-Phenylalanine; D015544:Inositol 1,4,5-Trisphosphate; D037342:Pertussis Toxin; D006596:Hexosaminidases; D002118:Calcium