P450 ARACHIDONATE METABOLITES MEDIATE BRADYKININ-DEPENDENT INHIBITIONOF NACL TRANSPORT IN THE RAT THICK ASCENDING LIMB

Recent studies from this laboratory demonstrated that bradykinin trans iently elevates intracellular Ca2+ and inhibits Cl- reabsorption in th e in vitro microperfused medullary thick ascending limb (mTAL) of the rat. The present study was designed to identify the intracellular sign aling mechanism(sf that mediate this response. Preincubation with the intracellular calcium chelator BAPTA (10(-5) M) completely eliminated the bradykinin-dependent increase in intracellular Ca2+ and the suppre ssion of Cl- transport. Preincubation with the cGMP-dependent protein kinase inhibitor H-89 (10(-5) M) had no effect on the transport respon se to bradykinin. In contrast, 17-octadecynoic acid(17-ODYA; 10(-5) M) , a suicide-substrate inhibitor of renal cytochrome P450 omega-hydroxy lase, completely blocked the transport response to bradykinin, while t he cyclooxygenase inhibitor sodium meclofenamate (10(-5) M) had no eff ect. Finally, addition of the cytochrome P450 omega-hydroxylase metabo lite 20-hydroxyeicosatetraenoic acid (20-HETE; 10(-8) M) to the bathin g medium significantly inhibited Cl- transport in the mTAL (Delta -39 +/- 6.0%; p < 0.05), while the epoxygenase metabolite 5,6-epoxyeicosat rienoic acid (5,6-EET; 10(-8) M) had no effect. These data suggest tha t the bradykinin-dependent inhibition of Cl- transport in the mTAL of the rat is mediated by cytochrome P450 dependent metabolite(s) of arac hidonic acid.