title: Endogenous flow-induced nitric oxide reduces superoxide-stimulated Na/H exchange activity via PKG in thick ascending limbs.
abstract: Luminal flow stimulates endogenous nitric oxide (NO) and superoxide (O2 (-)) production by renal thick ascending limbs (TALs). The delicate balance between these two factors regulates Na transport in TALs; NO enhances natriuresis, whereas O2 (-) augments Na absorption. Endogenous, flow-stimulated O2 (-) enhances Na/H exchange (NHE). Flow-stimulated NO reduces flow-induced O2 (-), a process mediated by cGMP-dependent protein kinase (PKG). However, whether flow-stimulated, endogenously-produced NO diminishes O2 (-)-stimulated NHE activity and the signaling pathway involved are unknown. We hypothesized that flow-induced NO reduces the stimulation of NHE activity caused by flow-induced O2 (-) via PKG in TALs. Intracellular pH recovery after an acid load was measured as an indicator of NHE activity in isolated, perfused rat TALs. l-Arginine, the NO synthase substrate, decreased NHE activity by 34 ± 5% (n = 5; P < 0.04). The O2 (-) scavenger tempol decreased NHE activity by 46 ± 8% (n = 6; P < 0.004) in the absence of NO. In the presence of l-arginine, the inhibitory effect of tempol on NHE activity was reduced to -19 ± 6% (n = 6; P < 0.03). The soluble guanylate cyclase inhibitor LY-83583 blocked the effect of l-arginine thus restoring tempol's effect on NHE activity to -42 ± 4% (n = 6; P < 0.0005). The PKG inhibitor KT-5823 also inhibited l-arginine's effect on tempol-reduced NHE activity (-43 ± 5%; n = 5; P < 0.03). We conclude that flow-induced NO reduces the stimulatory effect of endogenous, flow-induced O2 (-) on NHE activity in TALs via an increase in cGMP and PKG activation.
authors.affiliation: Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, Ohio nancy.hong@case.edu.
authors.forename: Nancy J
authors.initials: NJ
authors.lastname: Hong
authors.affiliation: Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, Ohio.
authors.forename: Jeffrey L
authors.initials: JL
authors.lastname: Garvin
mesh_terms: D000634:Aminoquinolines; D000818:Animals; D001120:Arginine; D002227:Carbazoles; D017869:Cyclic GMP-Dependent Protein Kinases / Q000378:metabolism*; D003497:Cyclic N-Oxides; D006863:Hydrogen-Ion Concentration; D008138:Loop of Henle / Q000378:metabolism*; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism*; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*; D013113:Spin Labels; D013481:Superoxides / Q000378:metabolism*
chemical_list: D000634:Aminoquinolines; D002227:Carbazoles; D003497:Cyclic N-Oxides; D017923:Sodium-Hydrogen Exchangers; D013113:Spin Labels; D013481:Superoxides; C073601:KT 5823; D009569:Nitric Oxide; C041715:6-anilino-5,8-quinolinedione; D001120:Arginine; D017869:Cyclic GMP-Dependent Protein Kinases; C001803:tempol
keywords: luminal flow; protein kinases; reactive oxygen species; sodium/hydrogen exchange