MK-886, a leukotriene biosynthesis inhibitor, as an activator of Ca(2+) mobilization in Madin-Darby canine kidney (MDCK) cells.

The effect of 3-¿1-(p-chlorobenzyl)-5-(isopropyl)-3-tert-butylthioindol-2-yl-2, 2-dimethylpropanoic acid (MK-886), a leukotriene biosynthesis inhibitor, on Ca(2+) mobilization in Madin- Darby canine kidney cells has been examined by fluorimetry using fura-2 as a Ca(2+) indicator. MK-886 at 0.5 to 25 microM concentration dependently increased ¿Ca(2+)(i). The ¿Ca(2+)(i) increase comprised an immediate initial rise and a slowly decaying phase. Ca(2+) removal inhibited the Ca(2+) signals by reducing both the initial rise and the decay phase, suggesting that MK-886 activated Ca(2+) influx and Ca(2+) release. In Ca(2+)-free medium, 10 microM MK-886 still increased ¿Ca(2+)(i) after pretreatment with carbonylcyanide m-chlorophenylhydrazone (CCCP; 2 microM), a mitochondrial uncoupler, and thapsigargin (1 microM), an endoplasmic reticulum Ca(2+) pump inhibitor. Conversely, pretreatment with MK-886 abolished CCCP- and thapsigargin-induced Ca(2+) release. This suggests that 10 microM MK-886 released Ca(2+) from the endoplasmic reticulum, mitochondria, and other stores. The addition of 3 mM Ca(2+) increased ¿Ca(2+)(i) after pretreatment with 10 microM MK-886 for 700 s in Ca(2+)-free medium, indicating that MK-886 induced capacitative Ca(2+) entry. This capacitative Ca(2+) entry was partly inhibited by SKF96365 (50 microM), by econazole (25 microM), and by inhibiting phospholipase A(2) with aristolochic acid (40 microM) but not by inhibiting phospholipase D with 0.1 mM propranolol. MK-886 (10 microM)-induced Ca(2+) release was not altered by inhibiting phospholipase C with U73122 (2 microM) but was inhibited by 50% by suppressing phospholipase D and phospholipase A(2) with propranolol (0.1 mM) and aristolochic acid (40 microM), respectively.