Autocrine effects of nitric oxide on HCO(3)(-) transport by rat thick ascending limb.
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.
Ortiz
P A
PA
Hypertension and Vascular Research Division, Henry Ford Hospital, Detroit, Michigan 48202, USA.
Garvin
J L
JL
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
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