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Nitric Oxide (NO) Regulates Paracellular Resistance in Isolated, Perfused Rat Thick Ascending Limbs through cGMP
Author(s) -
Monzon Casandra M,
Garvin Jeffrey L
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.967.9
Subject(s) - paracellular transport , nitric oxide , chemistry , arginine , nitric oxide synthase , endocrinology , permeability (electromagnetism) , medicine , biology , biochemistry , membrane , amino acid
Thick ascending limbs reabsorb30% of the filtered Na. About 50% traverses the paracellular pathway. We showed that exogenously‐added nitric oxide reduces the Na/Cl permeability ratio(PNa/PCl) of the paracellular pathway via cGMP/PKG, but the effects on absolute per meabilities are unknown. We hypothesized that endogenously‐produced NO decreases paracellular PNa in thick ascending limbs. To test this we measured the effect of L‐arginine (0.5 mM; NO synthase substrate) and cGMP (0.5 mM; NO's second messenger) on PNa and PCl calculated from PNa/PCl and transepithelial resistance. PNa/PCl was 2.0 ± 0.2 in the control period and 1.6± 0.1 after L‐arginine treatment (p<0.05). Transepithelial resistance (Rt) was 7722 ± 1554 ohm‐cm in the control period and 6318 ± 1757 ohm‐cm after L‐arginine (p<0.05). Calculated PNa and PCl were 0.361 ± 0.049 μm/sec and 0.181 ± 0.025μm/sec, respectively, in the control period. After L‐arginine they were 0.621 ± 0.158μm/sec and 0.388± 0.099 μm/sec, respectively. In the presence of the NOS inhibitor L‐NAME (5mM), L‐arginine had no significant effect on paracellular resistance (L‐NAME alone: 7924 ± 1964 ohm‐cm; vs L‐NAME + L‐arginine: 8463 ± 1725ohm‐cm). Next we tested the effect of cGMP. PNa/PCl was 2.6 ± 0.6 in the control period and 1.6 ± 0.2 after cGMP treatment (p<0.06). Rt in the control period was 7592 ± 1470 ohm‐cm and 4796 ± 847 ohm‐cm after cGMP (p<0.035). PNa and PCl were 0.390 ± 0.071 μm/sec and 0.150± 0.028 μm/sec, respectively, for the control period, and 0.550± 0.170 μm/sec and 0.340 ± 0.110 μm/sec, respectively, after db‐cGMP. We conclude that contrary to our hypothesis NO increased both PNa and PCl, and thus decreased transepithelial resistance. NO's effects are likely mediated by cGMP. The increases in PNa and PCl most likely contribute to elevated NaCl flux from bath to lumen along the thick ascending limb due to their electrochemical gradients in vivo and thus reduce net NaCl reabsorption. Support or Funding Information HL‐28982