cAMP-dependent fluid secretion in rat inner medullary collecting ducts

We used an unambiguous in vitro method to determine if inner medullary collecting ducts (IMCD) have intrinsic capacities to absorb and secrete solutes and fluid in an isotonic medium. IMCD1, IMCD2, and IMCD3 were dissected from kidneys of young Sprague-Dawley rats. 8-Bromo-3′,5′-cyclic monophosphate (8-BrcAMP) stimulated lumen formation and progressive dilation in all IMCD subsegments; lumen formation was greatest in IMCD1.Benzamil potentiated the rate of lumen expansion in response to 8-BrcAMP. Fluid entered tubule lumens by transcellular secretion rather than simple translocation of intracellular fluid. Secreted lumen solutes were osmometrically active. Inhibition of protein kinase A with H-89 and Rp diastereomer of adenosine 3′,5′-cyclic monophosphorothioate blocked fluid secretion. The rate of lumen expansion was reduced by the selective addition of ouabain, barium, diphenyl-2-carboxylate, bumetanide, glybenclamide, or DIDS, or reduction of extracellular Cl−. We conclude that IMCD absorb and secrete e...