Effect of m-3M3FBS on Ca²⁺ movement in Madin-Darby canine renal tubular cells

The effect of 2,4,6-trimethyl-N-(meta-3-trifluoromethyl-phenyl)- benzenesulfonamide (m-3M3FBS), a presumed phospholipase C (PLC) activator, on cytosolic free Ca²⁺ concentrations ([Ca²⁺]_i) in Madin-Darby canine kidney (MDCK) cells is unclear. This study explored whether m-3M3FBS changed basal [Ca²⁺]_i levels in suspended MDCK cells using fura-2 as a Ca²⁺-sensitive fluorescent dye. M-3M3FBS at concentrations between 0.1 and 20 1/4M increased [Ca²⁺]_i in a concentration-dependent manner. The Ca²⁺ signal was decreased by removing extracellular Ca²⁺. M-3M3FBS-induced Ca²⁺ influx was inhibited by the store-operated Ca²⁺ channel blockers nifedipine, econazole, and SK&F96365, and by the phospholipase A2 inhibitor aristolochic acid. In Ca²⁺-free medium, 20-1/4M m-3M3FBS pretreatment abolished the [Ca²⁺]_i rise induced by the endoplasmic reticulum Ca²⁺ pump inhibitors thapsigargin (TG) and cyclopiazonic acid (CPA). Conversely, pretreatment with TG or CPA partly reduced m-3M3FBS-induced [Ca²⁺]_i rise. The inhibition of PLC with U73122 did not alter m-3M3FBS-induced [Ca²⁺]_i rise. Collectively, in MDCK cells, m-3M3FBS induced [Ca²⁺]_i rises by causing PLC-independent Ca²⁺ release from the endoplasmic reticulum and Ca²⁺ influx via store-operated Ca²⁺ channels and other unidentified Ca²⁺ channels.