Bradykinin‐induced phosphoinositide hydrolysis and Ca 2+ mobilization in canine cultured tracheal epithelial cells

Experiments were designed to differentiate the mechanisms and subtype of kinin receptors mediating the changes in intracellular Ca 2+ concentration ([Ca 2+ ] i ) induced by bradykinin (BK) in canine cultured tracheal epithelial cells (TECs). BK and Lys‐BK caused an initial transient peak of [Ca 2+ ] i in a concentration‐dependent manner, with half‐maximal stimulation (pEC 50 ) obtained at 7.70 and 7.23, respectively. Kinin B 2 antagonists Hoe 140 (10 n M ) and [D‐Arg 0 , Hyp 3 , Thi 5,8 , D‐Phe 7 ]‐BK (1 μ M ) had high affinity in antagonizing BK‐induced Ca 2+ response with pK B values of 8.90 and 6.99, respectively. Pretreatment of TECs with pertussis toxin (100 ng ml −1 ) or cholera toxin (10 μg ml −1 ) for 24 h did not affect the BK‐induced IP accumulation and [Ca 2+ ] i changes in TECs. Removal of Ca 2+ by the addition of EGTA or application of Ca 2+ ‐channel blockers, verapamil, diltiazem, and Ni 2+ , inhibited the BK‐induced IP accumulation and Ca 2+ mobilization, indicating that Ca 2+ influx was required for the BK‐induced responses. Addition of thapsigargin (TG), which is known to deplete intracellular Ca 2+ stores, transiently increased [Ca 2+ ] i in Ca 2+ ‐free buffer and subsequently induced Ca 2+ influx when Ca 2+ was re‐added to this buffer. Pretreatment of TECs with TG completely abolished BK‐induced initial transient [Ca 2+ ] i , but had slight effect on BK‐induced Ca 2+ influx. Pretreatment of TECs with SKF96365 and U73122 inhibited the BK‐induced Ca 2+ influx and Ca 2+ release, consistent with the inhibition of receptor‐gated Ca 2+ ‐channels and phospholipase C in TECs, respectively. These results demonstrate that BK directly stimulates kinin B 2 receptors and subsequently phospholipase C‐mediated IP accumulation and Ca 2+ mobilization via a pertussis toxin‐insensitive G protein in canine TECs. These results also suggest that BK‐induced Ca 2+ influx into the cells is not due to depletion of these Ca 2+ stores, as prior depletion of these pools by TG has no effect on the BK‐induced Ca 2+ influx that is dependent on extracellular Ca 2+ in TECs.British Journal of Pharmacology (1999) 126 , 1341–1350; doi: 10.1038/sj.bjp.0702431