ELECTROGENIC SODIUM-ABSORPTION AND CHLORIDE SECRETION BY AN INNER MEDULLARY COLLECTING DUCT CELL-LINE (MIMCD-K2)

The initial segment of the inner medullary collecting duct (IMCD(i)) absorbs Na+ by an electrogenic mechanism and plays an important role in regulating the composition and-volume of the urine. The purpose of the present study was to establish a permanent cell line derived from the IMCD(i), which has the ion transport properties of the IMCD(i) in vivo. To this end, we isolated IMCD cells from the IMCD(i) of a mouse, Tg(SV40E) Bri 7, transgenic for the early region of SV40 (large T antigen) and established a permanent cell line, mIMCD-K2, by clonal dilution. mIMCD-K2 cells retain many differentiated characteristics of the IMCD(i), including amiloride-sensitive electrogenic Na+ absorption stimulated by nanomolar concentrations of aldosterone. Aldosterone (1.5 x 10(-6) M) increased Na+ absorption from 0.2 +/- 0.1 to 4.6 +/- 1.7 mu A/cm(2). In addition, the cells secrete Cl- by an electrogenic mechanism at a rate of 0.5 +/- 0.1 mu A/cm(2). We propose that IMCD(i) cells either absorb or secrete NaCl depending on NaCl homeostasis. The mIMCD-K2 cell line should be useful for studying the cellular mechanisms responsible for electrogenic Na+ and Cl- transport in the IMCD(i).