title: Autocrine effects of nitric oxide on HCO(3)(-) transport by rat thick ascending limb.
abstract: BACKGROUND
  In vivo and in vitro studies have shown that nitric oxide (NO) is an important modulator of transport processes along the nephron. The thick ascending limb (TAL) plays a significant role in the urine-concentrating mechanism and in the maintenance of acid/base balance.
  
  
  METHODS
  TALs from male Sprague-Dawley rats were isolated and perfused, and net bicarbonate flux (J(HCO3)(-) was determined.
  
  
  RESULTS
  In perfused TALs, 0.5 mmol/L L-arginine (L-Arg), the substrate for NO synthase, significantly lowered J(HCO3)(-) from 35.4 +/- 4.6 to 23.2 +/- 2.9 pmol. mm(-1). min(-1), a decrease of 36.9 +/- 11.6% (P < 0.025). D-Arg (0.5 mmol/L) had no effect on J(HCO3)(-) (N = 7). In the presence of 5 mmol/L L-NAME, an NO synthase (NOS) inhibitor, the addition of L-Arg did not affect TAL J(HCO3)(-) (43.4 +/- 4.4 vs. 44.6 +/- 5.0 pmol. mm(-1). min(-1)). L-NAME alone (5 mmol/L) did not affect TAL J(HCO3)(-). After removing L-Arg from the bath, J(HCO3)(-) increased from 26.2 +/- 3.9 to 34.8 +/- 3.2 pmol. mm(-1). min(-1) (P < 0.01), indicating no cytotoxicity of NO. We next investigated the effect of cGMP analogues on TAL J(HCO3)(-). 8-Br-cGMP (50 micromol/L) and db-cGMP (50 micromol/L) significantly decreased J(HCO3)(-) by 26.3 +/- 9.1% and 35.1 +/- 11.6%, respectively. In the presence of cGMP (50 micromol/L), the addition of L-Arg had no effect on J(HCO3)(-). In the presence of KT-5823 (2 mircromol/L), a protein kinase G inhibitor, the addition of L-Arg did not change TAL J(HCO3)(-) (N = 5).
  
  
  CONCLUSIONS
  We conclude that (1) endogenously produced NO inhibits TAL J(HCO3)(-) in an autocrine manner, (2) cGMP mediates all the effects of NO, and (3) this effect is mediated by protein kinase G activation.
authors.affiliation: Hypertension and Vascular Research Division, Henry Ford Hospital, Detroit, Michigan 48202, USA.
authors.forename: P A
authors.initials: PA
authors.lastname: Ortiz
authors.forename: J L
authors.initials: JL
authors.lastname: Garvin
mesh_terms: D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D001120:Arginine / Q000494:pharmacology; D019898:Autocrine Communication; D001639:Bicarbonates / Q000378:metabolism*; D001692:Biological Transport / Q000502:physiology; D002227:Carbazoles; D006152:Cyclic GMP / Q000031:analogs & derivatives / Q000502:physiology; D017869:Cyclic GMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066298:In Vitro Techniques; D007211:Indoles; D008138:Loop of Henle / Q000378:metabolism*; D008297:Male; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D000470:Alkaloids; D001639:Bicarbonates; D002227:Carbazoles; D004791:Enzyme Inhibitors; D007211:Indoles; C073601:KT 5823; D009569:Nitric Oxide; D001120:Arginine; D017869:Cyclic GMP-Dependent Protein Kinases; D006152:Cyclic GMP; D019331:NG-Nitroarginine Methyl Ester