Electrolyte and fluid secretion by cultured human inner medullary collecting duct cells

Abstract

Inner medullary collecting ducts (IMCD) are the final nephron segments through which urine flows. To investigate epithelial ion transport in human IMCD, we established primary cell cultures from initial (hIMCDi) and terminal (hIMCDt) inner medullary regions of human kidneys. AVP, PGE2, and forskolin increased cAMP in both hIMCDiand hIMCDtcells. The effects of AVP and PGE2were greatest in hIMCDi; however, forskolin increased cAMP to the same extent in hIMCDiand hIMCDt. Basal short-circuit current ( ISC) of hIMCDimonolayers was 1.4 ± 0.5 μA/cm2and was inhibited by benzamil, a Na+channel blocker. 8-Bromo-cAMP, AVP, PGE2, and forskolin increased ISC; the current was reduced by blocking PKA, apical Cl−channels, basolateral NKCC1 (a Na+-K+-2Cl−cotransporter), and basolateral Cl−/HCO[Formula: see text]exchangers. In fluid transport studies, hIMCDimonolayers absorbed fluid in the basal state and forskolin reversed net fluid transport to secretion. In hIMCDtmonolayers, basal current was not different from zero and cAMP had no effect on ISC. We conclude that AVP and PGE2stimulate cAMP-dependent Cl−secretion by hIMCDicells, but not hIMCDtcells, in vitro. We suggest that salt secretion at specialized sites along human collecting ducts may be important in the formation of the final urine.</jats:p