NITRIC OXIDE-20-HYDROXYEICOSATETRAENOIC ACID INTERACTION IN THE REGULATION OF K+ CHANNEL ACTIVITY AND VASCULAR TONE IN RENAL ARTERIOLES

The present study examined whether inhibition of P4504A enzyme activit y and the formation of 20-HETE contributes to the activation of K+ cha nnels and vasodilator effects of nitric oxide (NO) in renal arterioles . Addition of an NO donor to the P4504A2 enzyme that produces 20-HETE increased visible light absorbance at 440 nm indicating that NO binds to heme in this enzyme. NO donors also dose-dependently inhibited the formation of 20-HETE in microsomes prepared from renal arterioles. In patch-clamp experiments, NO donors increased the open-state probabilit y of a voltage-sensitive, large-conductance (195+/-9 pS) K+ channel re corded with cell-attached patches on renal arteriolar smooth muscle ce lls. Blockade of guanylyl cyclase with [1H-[1,2,4]Oxadiazolo[4,3-a] qu inoxalin-1-one] (ODQ, 10 mu mol/L), or cGMP-dependent kinase with myl- 8-methyl-2,3,9,10-tetrahydro-8-11-epoxy-1H,8H, rizadibenzo-(a,g)-cy-cl oocta-(c,d,e)-trinden-1-one (KT-5823) (1 mu mol/L) did not alter the e ffects of NO on this channel. In contrast, inhibition of the formation of 20-HETE with 17-octadecynoic acid (1 mu mol/L) activated this chan nel and masked the response to NO. Preventing the NO-induced reduction in intracellular 20-HETE levels also blocked the effects of NO on thi s channel. Sodium nitroprusside (SNP) increased the diaHETEr of renal interlobular arteries preconstricted with phenylephrine to 80+/-4% of control. Blockade of guanylyl cyclase with ODQ (10 mu mol/L) attenuate d the response to SNP by 26+/-2%; however, fixing 20-HETE levels at 10 0 nmol/L reduced the response by 67+/-8%. Blockade of both pathways el iminated the response to SNP. These results indicate that inhibition o f the formation of 20-HETE contributes to the activation of K+ channel s and the vasodilator effects of NO in the renal microcirculation.