ANION SECRETION DRIVES FLUID SECRETION BY MONOLAYERS OF CULTURED HUMAN POLYCYSTIC CELLS

We have investigated the hypothesis that active anion transport drives fluid secretion by the cystic epithelium in autosomal dominant polycy stic kidney disease (ADPKD). We prepared monolayers of a primary cultu re derived from cystic tissue removed from ADPKD patients. The monolay ers were grown on permeant supports, and fluid secretion was initiated by forskolin. The results were compared with those obtained with mono layers of Madin-Darby canine kidney (MDCK) cells, known to secrete Cl- . In the absence of the agonist, ADPKD monolayers absorbed fluid (0.20 +/- 0.02 mu l . cm surface area(-2). h(-1)). Forskolin reversed this to secretion (0.60 +/- 0.03 mu l . cm(-2). h(-1)). Control MDCK monola yers did not transport fluid in either direction, but forskolin induce d secretion (0.48 +/- 0.03 mu l . cm(-2). h(-1)). The electrical prope rties of the monolayers were monitored in Ussing chambers. Forskolin i ncreased the transepithelial potential difference (V-te) of ADPKD mono layers (-0.9 +/- 0.1 to -1.1 +/- 0.1 mV) and the short-circuit current (I-sc) (6.6 +/- 0.7 to 9.2 +/- 0.8 mu A/cm(2)). The transepithelial r esistance (R(te)) fell (156 +/- 9 to 138 +/- 10 Omega . cm(2)). Simila r results were obtained with MDCK monolayers. The polarity of V-te and the direction of the I-sc are compatible with the hypothesis that act ive secretion of anion drives fluid secretion. Basolateral application of the Na-K-2Cl cotransporter, bumetanide, reduced forskolin-stimulat ed fluid secretion by ADPKD monolayers (0.56 +/- 0.05 to 0.28 +/- 0.03 ), depolarized V-te, and inhibited I-sc without affecting R(te). Apica l application of the Cl- channel blocker, diphenylamine-2-carboxylate, also inhibited fluid secretion by ADPKD monolayers (0.65 +/- 0.03 to 0.27 +/- 0.02 mu l . cm(-2). h(-1)). It also depolarized V-te and decr eased I-sc. The two inhibitors exerted similar effects on MDCK monolay ers. These results substantiate the hypothesis that active transepithe lial transport of anion may drive fluid secretion into ADPKD cysts.