In vitro fluid secretion by epithelium from polycystic kidneys

Abstract

The size of the kidneys in patients with autosomal dominant polycystic kidney disease (ADPKD) is due in large measure to the accumulation of secreted fluid within thin-walled epithelial sacs. We measured the net transepithelial movement of liquid in response to forskolin in isolated, intact cysts excised from the surface of human ADPKD kidneys and in cultured, polarized monolayers of epithelial cells derived from ADPKD cysts. 10 excised cysts bathed symmetrically in control culture medium secreted fluid at a rate of 0.19±0.03 μl/cm2 per hour after stimulation with forskolin (10 μM). Ouabain (100 μM) addition to the cavity fluid did not change the rate of fluid secretion of 10 forskolin-treated cysts, but addition of the glycoside to the external bathing medium fluid of nine cysts decreased secretion to - 0.004±0.05 μl/cm2 per hour. 24 monolayers absorbed fluid (range -0.029 to -0.412 μl/cm2 per hour); by contrast, fluid was secreted (range 0.074 to 1.242 μl/cm2 per hour) after stimulation with forskolin (10 μM). Ouabain (0.1 μM) in the basolateral but not in the apical medium inhibited fluid secretion. Forskolin increased the intracellular cyclic AMP content of ADPKD and MDCK monolayers by 236 and 196%, respectively. Six ADPKD monolayers had stable lumen negative transepithelial electrical potential differences (PD(te)) of -1.4±0.3 mV, positive short circuit currents (SCC) of 11.9±2.1 μAmp/cm2 and a tissue resistance (R(te)) of 116±14 ohm · cm2. Forskolin increased SCC to 15.5±1.9 μAmp/cm2 (P < 0.005) and decreased R(te) to 95±13 ohm · cm2 (P < 0.05); PD(te) remained stable at -1.4±0.3 mV. Ouabain (10 μM) had no effect when added to the apical medium, but in the basolateral medium decreased SCC to 1.7±0.3 μAmp/cm2 and PD(te) to - 0.2±0.1 mV. We conclude that ADPKD cells in surface cysts have the potential to absorb or to secrete solutes and fluid. cAMP-mediated fluid secretion from the basolateral medium into the lumen of surface ADPKD cysts may be driven by anion transport.