Nitric Oxide-20–Hydroxyeicosatetraenoic Acid Interaction in the Regulation of K + Channel Activity and Vascular Tone in Renal Arterioles

Abstract

Abstract —The present study examined whether inhibition of P4504A enzyme activity and the formation of 20-HETE contributes to the activation of K + channels 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 probability of a voltage-sensitive, large-conductance (195±9 pS) K + channel recorded with cell-attached patches on renal arteriolar smooth muscle cells. Blockade of guanylyl cyclase with [1H-[1,2,4]Oxadiazolo[4,3-a] quinoxalin-1-one] (ODQ, 10 μmol/L), or cGMP-dependent kinase with 8 R ,9 S ,11 S -(−)-9-methoxycarbamyl-8-methyl-2,3,9,10-tetrahydro-8,11-epoxy-1 H ,8 H ,11 H -2,7 b ,11 a -trizadibenzo-( a , g )-cy-cloocta-( c , d , e )-trinden-1-one (KT-5823) (1 μmol/L) did not alter the effects of NO on this channel. In contrast, inhibition of the formation of 20-HETE with 17-octadecynoic acid (1 μmol/L) activated this channel and masked the response to NO. Preventing the NO-induced reduction in intracellular 20-HETE levels also blocked the effects of NO on this channel. Sodium nitroprusside (SNP) increased the diameter of renal interlobular arteries preconstricted with phenylephrine to 80±4% of control. Blockade of guanylyl cyclase with ODQ (10 μmol/L) attenuated the response to SNP by 26±2%; however, fixing 20-HETE levels at 100 nmol/L reduced the response by 67±8%. Blockade of both pathways eliminated the response to SNP. These results indicate that inhibition of the formation of 20-HETE contributes to the activation of K + channels and the vasodilator effects of NO in the renal microcirculation.