Abstract
Transepithelial fluid secretion is an important process in the progressive enlargement of certain types of renal cysts. Arginine vasopressin (AVP) increases the rate of cyst formation and expansion in an in vitro model of renal cysts that uses Madin-Darby canine kidney (MDCK) cells grown in a gelled matrix of Type 1 collagen. In this study, it was determined if AVP promoted net fluid secretion by MDCK cells. The rate of volumetric fluid secretion was determined from the net movement of water across epithelial layers of MDCK cells grown on permeable, collagen-coated membranes. AVP in the basolateral medium (but not in apical medium) at concentrations exceeding 10(-9) M caused sustained basolateral to apical transepithelial fluid secretion (approximately 0.6 microL/cm2/h). 1-Desamino-8-D-AVP, a V2 receptor agonist, had a similar effect. The secreted fluid was hyperosmotic compared with the bath (5.7 to 9.7 mosM). Chloride was consistently secreted, but the absolute level in the secreted fluid was variable. Intracellular cAMP content was increased 187% by a 2-h exposure to AVP and 10(-4) M methylisobutylxanthine. Net fluid secretion was augmented by methylisobutylxanthine and theophylline and was inhibited by ouabain, bumetanide, and a sodium-dependent Cl-/HCO3- exchange inhibitor (L-645,695) but was not altered by clonidine, guanabenz, or indomethacin. AVP-induced fluid secretion was not accompanied by a change in transepithelial hydraulic conductivity. It is suggested that AVP stimulates fluid secretion of MDCK epithelial monolayers by activating V2 receptor-mediated adenylate cyclase. The regulation of net fluid secretion by AVP would appear to depend on modulation of solute transport, rather than on water permeability.
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