8-iso-prostaglandin-F2α stimulates chloride transport in thick ascending limbs: Role of cAMP and protein kinase A

Abstract

Salt reabsorption by the loop of Henle controls NaCl handling and blood pressure regulation. Increased oxidative stress stimulates NaCl transport in one specific segment of the loop of Henle called the thick ascending limb (TAL). The isoprostane 8-iso-prostaglandin-F2á (8-iso-PGF2á) is one of the most abundant nonenzymatic lipid oxidation products and has been implicated in the development of hypertension. However, it is not known whether 8-iso-PGF2á regulates transport or the mechanisms involved. Because protein kinase A (PKA) stimulates NaCl transport in several nephron segments, we hypothesized that 8-iso-PGF2á increases NaCl transport in the cortical TAL (cTAL) via a PKA-dependent mechanism. We examined the effect of luminal 8-iso-PGF2á on NaCl transport by measuring chloride absorption (J Cl) in isolated microperfused cTALs. Adding 8-iso-PGF2á to the lumen increased JCl by 54% (from 288.7 ± 30.6 to 446.5 ± 44.3 pmol·min-1·mm-1; P < 0.01), while adding it to the bath enhanced JCl by 35% (from 236.3 ± 35.3 to 319.2 ± 39.8 pmol·min-1·mm -1; P < 0.05). This stimulation was blocked by Na-K-2Cl cotransporter inhibition. Next, we tested the role of cAMP. Basal cAMP in the cTAL was 18.6 ± 1.6 fmol·min-1·mm-1, and 8-iso-PGF2á raised it to 35.1 ± 1.4 fmol·min -1·mm-1, an increase of 94% (P < 0.01). Because cAMP stimulates PKA, we measured JCl using the PKA-selective inhibitor H89. In the presence of H89 (10 ìM), 8-iso-PGF2á failed to increase transport regardless of whether it was added to the lumen (216.1 ± 16.7 vs. 209.7 ± 23.8 pmol·min -1·mm-1; NS) or the bath (150.4 ± 32.9 vs. 127.1 ± 28.6 pmol·min-1·mm-1; NS). We concluded that 8-iso-PGF2á stimulates cAMP and increases Cl transport in cTALs via a PKA-dependent mechanism.