Leukotriene D4-induced increases in cytosolic calcium in THP-1 cells: dependence on extracellular calcium and inhibition with selective leukotriene D4 receptor antagonists.
Agonist-induced changes in intracellular calcium ion concentration ([Ca++]i) were examined in human monocytic leukemia THP-1 cells loaded with fura 2/acetoxymethyl ester (fura 2/AM). Leukotriene (LT)D4 induced a concentration-dependent biphasic response consisting of a transient phase (up to 5-fold peak increase) followed by a sustained phase, showing characteristics of a receptor-operated calcium channel. Homologous desensitization to LTD4 was observed. The responses to LTD4 were reduced by 80 to 90% in calcium-free buffer. The responses to LTD4 in a calcium-free buffer were dependent upon the duration of prior exposure of the cells to a calcium-free environment. The response at 30 or 60 min after exposure to calcium-free buffer was greater than that at earlier time points (time-dependent sensitization). Similar responses were obtained with THP-1 cells exposed to EDTA-containing buffer. It is speculated that such time-dependent sensitization is a result of changes at the receptor level. The responses to LTD4 were blocked by two specific LTD4 antagonists, MK-0571 and ICI-204,219, in a concentration-dependent manner. When given after addition of LTD4, MK-0571 or ICI-204,219 reversed the sustained phase of the LTD4-induced response, suggesting that maintenance of the response requires persistent activation of the LTD4 receptor. ICI-204,219 was 5 to 10 times more potent than MK-0571 (IC50 values of 1.1 and 9.3 nM, respectively), in agreement with results from radioligand binding studies reported separately.
Department of Pharmacology, Merck Frosst Centre for Therapeutic Research, Kirkland, Quebec, Canada.
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CC
Chan
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Ecclestone
D W
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Nicholson
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Metters
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Pon
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Rodger
D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D006801:Humans; D007211:Indoles; D007951:Leukemia, Myeloid / Q000378:metabolism*; D020024:Leukotriene Antagonists; D017998:Leukotriene D4 / Q000494:pharmacology*; D008565:Membrane Proteins; D048448:Phenylcarbamates; D011422:Propionates / Q000494:pharmacology; D011804:Quinolines / Q000494:pharmacology; D018077:Receptors, Leukotriene / Q000502:physiology*; D013449:Sulfonamides; D014105:Tosyl Compounds / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D007211:Indoles; D020024:Leukotriene Antagonists; D008565:Membrane Proteins; D048448:Phenylcarbamates; D011422:Propionates; D011804:Quinolines; D018077:Receptors, Leukotriene; D013449:Sulfonamides; D014105:Tosyl Compounds; C059141:verlukast; D017998:Leukotriene D4; C412375:cysteinyl leukotriene receptor 2; C083169:leukotriene D4 receptor; D002118:Calcium; C062735:zafirlukast