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1 Kidney Institute and Departments of 2 Biochemistry and Molecular Biology, 3 Medicine, and 4 Urology, University of Kansas Medical Center, Kansas City, Kansas 66160
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
(ISC) 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 ISC; the current was
reduced by blocking PKA, apical Cl
channels, basolateral
NKCC1 (a Na+-K+-2Cl
cotransporter), and basolateral Cl
/HCO
secretion by
hIMCDi cells, but not hIMCDt cells, in vitro.
We suggest that salt secretion at specialized sites along human
collecting ducts may be important in the formation of the final urine.
kidney; chloride transport; salt secretion
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