COMPARATIVE EFFECTS OF CYTOCHROME-P-450 INHIBITORS ON CA-2+ AND MN-2+ ENTRY INDUCED BY AGONISTS OR BY EMPTYING THE CA-2+ STORES OF HUMAN NEUTROPHILS

The effects of cytochrome P-450 inhibitors of different chemical structures, including several imidazole antimycotics, SYF525A, 5,8,11,14-eicosatetraynoic acid (ETYA), gossypol and nordihydroguaiaretic acid (NDGA), were tested on the entry of Ca2+ and Mn2+ induced either by emptying the intracellular Ca2+ stores with thapsigargin or by stimulation with platelet activating factor (PAF). Most of the drugs inhibited thapsigargin-induced Ca3+ and Mn2+ entry with the same affinity, with the striking exceptions of econazole and miconazole, which were 5- and 2-fold more potent to inhibit the thapsigargin-induced Mn2+ entry than to inhibit Ca2+ entry, respectively. Additionally, high doses of every drug (3-10-times the K(i)) activated a pathway permeable to Mn2+ and Ni2+ but not to Ca2+. These findings indicate that Mn2+ entry data should be interpreted with caution and always be cross-checked with Ca2+ uptake measurements. Most of the drugs inhibited PAF-induced Mn2+ uptake with an affinity similar to that found for thapsigargin-induced Mn2+ uptake. PAF- and thapsigargin-induced Ca2+ uptake were also inhibited similarly by NDGA, SKF525A and gossypol, but PAF-induced Ca2+-uptake was inhibited about 5-fold more strongly by econazole and ETYA and two-fold more strongly by miconazole and clotrimazole. These findings suggest that the Ca2+/Mn2+ entry pathway opened by agonists in human neutrophils is the same that activates on emptying the Ca2+ stores and that cytochrome P450 activity may be involved en the activation of the channels.