VASOPRESSIN AND CAMP STIMULATE ELECTROGENIC CHLORIDE SECRETION IN AN IMCD CELL-LINE

Previously, we demonstrated that the mIMCD-K2 cell line, derived from the inner medullary collecting duct (IMCD) of a transgenic mouse, secretes Cl- by an electrogenic mechanism [N. L. Kizer, B. Lewis, and B. A. Stanton. Am. J. Physiol. 268 (Renal Fluid Electrolyte Physiol. 37): F347-F355, 1995]. The objective of the present study was to characterize the cellular mechanisms of electrogenic Cl- secretion (I-sc(Cl)) and to determine whether arginine vasopressin (AVP) and adenosine 3',5'-cyclic monophosphate (cAMP) stimulate I-sc(Cl). To this end, we measured I-sc(Cl) across monolayers of mIMCD-K2 cells mounted in Ussing-type chambers. AVP increased I-sc(Cl) with a Michaelis constant (K-m) of 2.1 +/- 0.7 x 10(-12) M. 1-Desamino-8-D-AVP, a specific V-2 receptor agonist, increased I-sc(CL) from 3.3 +/ 0.4 to 17.4 +/- 1.3 mu A/cm(2). 8-(4-Chlorophenylthio)-cAMP, a cell-permeant analogue of cAMP, a second messenger of AVP, increased I-sc(Cl) from 1.4 +/- 0.3 to 15.2 +/- 1.2 mu A/cm(2). Furosemide and bumetanide, inhibitors of Na+-2Cl(-)-K+ cotransport, and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), an inhibitor of Cl-/ HCO, exchange, reduced I-sc(Cl) when added to the basolateral solution. Our data suggest that AVP, via V-2 receptors, and the second messenger cAMP stimulate I-sc(Cl) and that Cl- secretion by mIMCD-K2 cells involves uptake of Cl- across the basolateral membrane by Na+-2Cl(-)-K+ cotransport and Cl-/HCO3- exchange and diffusion out of the cells across the apical membrane by cystic fibrosis transmembrane conductance regulator Cl- channels.