Nitric oxide-inhibited chloride transport in cortical thick ascending limbs is reversed by 8-iso-prostaglandin-F2 alpha

Background: Sodium chloride (NaCl) reabsorption in the cortical thick ascending limb (cTAL) is regulated by opposing effects. Nitric oxide (NO) inhibits NaCl reabsorption while 8-iso-prostaglandin-F2 alpha (8-iso-PGF2 alpha) stimulates it. Their interaction has not been evalu-ated in the cTAL. Because 8-iso-PGF2 alpha has considerable stability while NO is a free radical with a short half-life, we hypothesized that, in the cTAL, the inhibition of NaCl absorption will be reversed by 8-iso-PGF2 alpha.Methods: Chloride absorption (JCl) was measured in isolated perfused cTALs and whether the activation of protein kinase A (PKA) is required for this interaction. Since cyclic adenosine monophosphate (cAMP) is a major messenger for the 8-iso-PGF2 alpha signaling cas-cade, and NO inhibits JCl by decreasing cAMP bioavailability, we measured 8-iso-PGF2 alpha-stimulated cAMP in the presence of sodium nitroprusside (SNP).Results: The NO donor, SNP (10-6 M), decreased JCl by 41%, while luminal 8-iso-PGF2 alpha (100 mu M) increased JCl to 315 +/- 46 pmol/ min/mm (p < 0.003), reversing the effects of the NO donor. SNP inhibited JCl, 8-iso-PGF2 alpha failed to increase JCl in the presence of H89. Basal cAMP was 56 +/- 13 fmol/min/mm, in the presence of SNP 57 +/- 6 fmol/min/mm, and 8-iso-PGF2 alpha increased it to 92 +/- 2 fmol/min/mm (p < 0.04).Conclusion: We concluded that 1) NO-induced inhibition of JCl in the cTAL can be reversed by 8-iso-PGF2 alpha, 2) 8-iso-PGF2 alpha and NO in-teraction requires PKA to control JCl, and 3) in the presence of NO, 8-iso-PGF2 alpha continues to stimulate JCl because NO cannot reverse 8-iso-PGF2 alpha-stimulated cAMP level.