Superoxide enhances tubuloglomerular feedback by constricting the afferent arteriole.
BACKGROUND
Superoxide (O(2) (-)) has been shown to augment tubuloglomerular feedback (TGF) both in vivo and in vitro by scavenging nitric oxide (NO) in the macula densa (MD). We hypothesized that in addition to this mechanism O(2) (-) potentiates TGF by acting directly on the afferent arteriole (Af-Art).


METHODS
Microdissected Af-Arts and adherent tubular segments containing the MD were simultaneously microperfused in vitro, maintaining Af-Art pressure at 60 mm Hg. TGF response was determined by measuring changes in Af-Art diameter while increasing NaCl in the MD perfusate from 11/10 to 81/80 mmol/L Na/Cl.


RESULTS
To determine whether O(2) (-) acts at the MD in the absence of MD NO, we inhibited MD nNOS with 7-nitroindazole (7-NI) and added Tempol to the lumen. When 7-NI was added to the MD lumen, it increased TGF from 2.3 +/- 0.2 to 4.2 +/- 0.2 microm (P < 0.01). When Tempol was added to the MD lumen in the presence of 7-NI, it had no effect on TGF. To investigate whether O(2) (-) has any effect via the Af-Art in the absence of MD NO, we inhibited MD nNOS with 7-NI and added Tempol to the bath to scavenge O(2) (-) in the Af-Art. Adding Tempol to the bath with 7-NI in the MD lumen reduced TGF from 3.9 +/- 0.3 to 2.8 +/- 0.5 microm (P < 0.05 vs. 7-NI). To see if this effect was due to O(2) (-) scavenging NO production by the endothelium, we repeated the experiment in Af-Arts with damaged endothelium and found that adding Tempol to the bath lowered TGF from 3.4 +/- 0.9 to 1.2 +/- 0.6 microm (P < 0.01). When catalase was added to the bath together with Tempol, TGF response was not modified.


CONCLUSIONS
We concluded that it is O(2) (-) rather than H(2)O(2) that enhances TGF response, both directly by constricting the Af-Art and indirectly by scavenging NO in the MD.
Liu
Ruisheng
R
Division of Hypertension and Vascular Research, Henry Ford Hospital, Detroit, Michigan, USA.
Ren
YiLin
Y
Garvin
Jeffrey L
JL
Carretero
Oscar A
OA
D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D001160:Arterioles / Q000502:physiology*; D003165:Complement System Proteins / Q000494:pharmacology; D003497:Cyclic N-Oxides / Q000494:pharmacology; D004730:Endothelium, Vascular / Q000187:drug effects / Q000503:physiopathology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D025461:Feedback, Physiological / Q000502:physiology*; D016166:Free Radical Scavengers / Q000494:pharmacology; D007191:Indazoles / Q000494:pharmacology; D007678:Kidney Glomerulus / Q000502:physiology*; D007684:Kidney Tubules / Q000502:physiology*; D008297:Male; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism; D052248:Nitric Oxide Synthase Type I; D011817:Rabbits; D012079:Renal Circulation; D013113:Spin Labels; D013481:Superoxides / Q000378:metabolism*; D015291:Transforming Growth Factors / Q000378:metabolism; D014661:Vasoconstriction / Q000502:physiology*; D014662:Vasoconstrictor Agents / Q000378:metabolism*
D000906:Antibodies; D003497:Cyclic N-Oxides; D004791:Enzyme Inhibitors; D016166:Free Radical Scavengers; D007191:Indazoles; D013113:Spin Labels; D014662:Vasoconstrictor Agents; D013481:Superoxides; D015291:Transforming Growth Factors; D003165:Complement System Proteins; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I; C001803:tempol; C080122:7-nitroindazole