Angiotensin II-NAD(P)H oxidase-stimulated superoxide modifies tubulovascular nitric oxide cross-talk in renal outer medulla

Abstract

The source of superoxide (O2.-) production and cell-to-cell interactions of O2.- and nitric oxide (NO) in response to angiotensin II (AngII) were studied by fluorescence microscopic techniques to image rat renal outer medullary microtissue strips. Changes in intracellular O2.- were determined by dihydroethidium-ethidium ratios, and NO was determined with 4,5-diaminofluorescein diacetate. AngII (1 μmol/L) significantly increased O2.- in the isolated, medullary thick ascending limb (mTAL). These responses were inhibited by the superoxide dismutase mimetic 4-hydroxytetramethylpiperidine-1-oxyl (TEMPOL) and by the NAD(P)H oxidase inhibitors diphenylene iodonium and apocynin. AngII did not increase O 2.- in either pericytes of isolated, intact vasa recta (VR) or pericytes of VR with a disrupted endothelium, even when surrounded by mTAL. However, AngII did increase O2.- when the tissue strips were preincubated with the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (carboxy-PTIO), indicating that cross-talk of O2.- from mTAL to the VR occurred but was normally inhibited by NO. Also, tissue O 2.- reduction by TEMPOL increased the diffusion of NO from mTAL to the pericytes, indicating that cross-talk of NO from the mTAL to the VR is also inhibited by O2.-. We conclude that AngII stimulates O2.- production in mTAL via the NAD(P)H oxidase pathway and that interactions of O2.- and NO ultimately determine the effectiveness of in situ free-radical cross-talk between the mTAL and the VR.