Bradykinin (BK) and solute transport in the medullary thick ascending limb (mTAL) of the rat

We have previously reported that BK, acting via a basolateral membrane B2 receptor, transiently increases intracellular calcium and inhibits NaCI transport in the in vitro microperfijsed mTAL of the rat (Eur. J. Pharmacol. 1995, In Press). The present study utilized in vitro microperiusion to determine the intracellular signaling pathway(s) underlying this effect. The BK-mediated reduction in Cl" transport was prevented by preincubation with the intracellular calcium chelator B APT A (1 μuM) indicating that this response is dependent on the rise in cvtosolic calcium. Incubation with the protein kinase G inhibitor H-89 (10μM) did not alter the BK response, suggesting that the inhibition of Cl^- transport is not mediated via increases in cyclic GMP. In contrast, the reduction of Cl^- transport typically seen with BK (93.1 ±8.6 to 54.1 ±9.4 pEq/mm/min; p< 0.005; n=6) was completely blocked by pretreatment with the cytochrome P450 monooxygenase inhibitor 17ODYA (10nM) (118.3 ±26.3 to 112.0 ±22.5, n=5), but not by the cyclooxygenase/lipoxygenase inhibitor meclofenamate. These data suggest that the BK-mediated inhibition of Cl' transport in the mTAL of the rat is due to a calcium-dependent increase in cytochrome P450dependent arachidonic acid metabolism.