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

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 hIMCDi and hIMCDt cells. The effects of AVP and PGE2 were greatest in hIMCDi; however, forskolin increased cAMP to the same extent in hIMCDi and hIMCDt. Basal short-circuit current (I SC) of hIMCDi monolayers was 1.4 ± 0.5 μA/cm2 and was inhibited by benzamil, a Na+ channel blocker. 8-Bromo-cAMP, AVP, PGE2, and forskolin increased I SC; the current was reduced by blocking PKA, apical Cl− channels, basolateral NKCC1 (a Na+-K+-2Cl−cotransporter), and basolateral Cl−/HCO 3 − exchangers. In fluid transport studies, hIMCDi monolayers absorbed fluid in the basal state and forskolin reversed net fluid transport to secretion. In hIMCDt monolayers, basal current was not different from zero and cA...