Hyperosmolality inhibits sodium absorption and chloride secretion in mIMCD-K2 cells.

Previously we demonstrated that a cell line derived from mouse inner medullary collecting duct (mIMCD-K2) absorbs Na+ and secretes Cl- by electrogenic mechanisms and that arginine vasopressin (AVP) stimulates Cl- secretion. The objective of the present study was to determine whether hyperosmolality, both acute (minutes) and chronic (weeks), affects electrogenic Na+ absorption IscNa and electrogenic Cl- secretion IscCl across the IMCD. To this end, we measured IscNa and IscCl across monolayers of mIMCD-K2 cells mounted in Ussing-type chambers. Osmolality was increased from 290 to 590 mosmol/kgH2O by adding 200 mosmol/kgH2O of NaCl and 100 mosmol/kgH2O of urea or 300 mosmol/kgH2O of sucrose to the bathing solutions. Acute and chronic hyperosmolality reduced basal IscNa and IscCl and the AVP-stimulated rise in IscCl. These findings indicate that osmolality is an important determinant of IscNa and IscCl across IMCD cells and that the osmolality of the interstitial fluid should be considered when evaluating the effects of hormones and other factors on Na+ and Cl- transport by the IMCD.