MK-886, a leukotriene biosynthesis inhibitor, as an activator of Ca²⁺ mobilization in Madin-Darby canine kidney (MDCK) cells

The effect of 3-[1-(p-chlorobenzyl)-5-(isopropyl)-3-tert-butyl- thioindol-2-yl]-2, 2-dimethylpropanoic acid (MK-886), a leukotriene biosynthesis inhibitor, on Ca²⁺ mobilization in Madin-Darby canine kidney cells has been examined by fluorimetry using fura-2 as a Ca²⁺ indicator. MK-886 at 0.5 to 25 μM concentration dependently increased [Ca²⁺](i). The [Ca²⁺](i) increase comprised an immediate initial rise and a slowly decaying phase. Ca²⁺ removal inhibited the Ca²⁺ signals by reducing both the initial rise and the decay phase, suggesting that MK-886 activated Ca²⁺ influx and Ca²⁺ release. In Ca²⁺-free medium, 10 μM MK-886 still increased [Ca²⁺](i) after pretreatment with carbonylcyanide m- chlorophenylhydrazone (CCCP; 2 μM), a mitochondrial uncoupler, and thapsigargin (1 μM), an endoplasmic reticulum Ca²⁺ pump inhibitor. Conversely, pretreatment with MK-886 abolished CCCP- and thapsigargin-induced Ca²⁺ release. This suggests that 10 μM MK-886 released Ca²⁺ from the endoplasmic reticulum, mitochondria, and other stores. The addition of 3 mM Ca²⁺ increased [Ca²⁺](i) after pretreatment with 10 μM MK-886 for 700 s in Ca²⁺-free medium, indicating that MK-886 induced capacitative Ca²⁺ entry. This capacitative Ca²⁺ entry was partly inhibited by SKF96365 (50 μM), by econazole (25 μM), and by inhibiting phospholipase A₂ with aristolochic acid (40 μM) but not by inhibiting phospholipase D with 0.1 mM propranolol. MK-886 (10 μM)-induced Ca²⁺ release was not altered by inhibiting phospholipase C with U73122 (2 μM) but was inhibited by 50% by suppressing phospholipase D and phospholipase A₂ with propranolol (0.1 mM) and aristolochic acid (40 μM), respectively.