Nitric oxide-inhibited chloride transport in cortical thick ascending limbs is reversed by 8-iso-prostaglandin-F2α

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-F2α (8-iso-PGF2α) stimulates it. Their interaction has not been evaluated in the cTAL. Because 8-iso-PGF2α 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-PGF2α. METHODS: Chloride absorption (J(Cl)) 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-PGF2α signaling cascade, and NO inhibits J(Cl) by decreasing cAMP bioavailability, we measured 8-iso-PGF2α–stimulated cAMP in the presence of sodium nitroprusside (SNP). RESULTS: The NO donor, SNP (10(–6) M), decreased J(Cl) by 41%, while luminal 8-iso-PGF2α (100 μM) increased J(Cl) to 315 ± 46 pmol/min/mm (p < 0.003), reversing the effects of the NO donor. SNP inhibited J(Cl), 8-iso-PGF2α failed to increase J(Cl) 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-PGF2α increased it to 92 ± 2 fmol/min/mm (p < 0.04). CONCLUSION: We concluded that 1) NO-induced inhibition of J(Cl) in the cTAL can be reversed by 8-iso-PGF2α, 2) 8-iso-PGF2α and NO interaction requires PKA to control J(Cl), and 3) in the presence of NO, 8-iso-PGF2α continues to stimulate J(Cl) because NO cannot reverse 8-iso-PGF2α-stimulated cAMP level.