1. Experiments were designed to differentiate the mechanisms and subtype of kinin receptors mediating the changes in intracellular Ca2+ concentration ([Ca2+](i)) induced by bradykinin (BK) in canine cultured tracheal epithelial cells (TECs). 2. BK and Lys-BK caused an initial transient peak of [Ca2+](i) in a concentration-dependent manner, with half-maximal stimulation (pEC50) obtained at 7.70 and 7.23, respectively. 3. Kinin B2 antagonists Hoe 140 (10 nM) and [D-Arg0, Hyp3, Thi5.8, D-Phe7]-BK (1 μM) had high affinity in antagonizing BK-induced Ca2+ response with pK(B) values of 8.90 and 6.99, respectively. 4. 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 [Ca2+](i) changes in TECs. 5. Removal of Ca2+ by the addition of EGTA or application of Ca2+-channel blockers, verapamil, diltiazem, and Ni2+, inhibited the BK-induced IP accumulation and Ca2+ mobilization, indicating that Ca2+ influx was required for the BK-induced responses. 6. Addition of thapsigargin (TG), which is known to deplete intracellular Ca2+ stores, transiently increased [Ca2+](i) in Ca2+-free buffer and subsequently induced Ca2+ influx when Ca2+ was re-added to this buffer. Pretreatment of TECs with TG completely abolished BK-induced initial transient [Ca2+](i), but had slight effect on BK-induced Ca2+ influx. 7. Pretreatment of TECs with SKF96365 and U73122 inhibited the BK-induced Ca2+ influx and Ca2+ release, consistent with the inhibition of receptor-gated Ca2+-channels and phospholipase C in TECs, respectively. 8. These results demonstrate that BK directly stimulates kinin B2 receptors and subsequently phospholipase C-mediated IP accumulation and Ca2+ mobilization via a pertussis toxin-insensitive G protein in canine TECs. These results also suggest that BK-induced Ca2+ influx into the cells is not due to depletion of these Ca2+ stores, as prior depletion of these pools by TG has no effect on the BK-induced Ca2+ influx that is dependent on extracellular Ca2+ in TECs.
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