Vasopressin-enhanced urea transport by rat inner medullary collecting duct cells in culture

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Abstract
The distal inner medullary collecting duct (IMCD) is critical in the urinary concentrating process, in part because it is the site of vasopressin (AVP)-regulated permeability to urea. The purpose of these experiments was to develop a cell culture model of the IMCD on permeable structure and to characterize the responsiveness to AVP. Rat IMCD cells were grown to confluence on collagen-coated Millipore filters glued onto plastic rings. To assess the time required to achieve confluence, the transepithelial resistance was measured periodically and was found to be stable after 2 weeks, at a maximal value of 595 .+-. 22 .OMEGA. cm2. In separate monolayers the effect of AVP on inulin and urea permeability was determined. While inulin permeability was unchanged after AVP, urea permeability increased from 6.0 .+-. 0.4 to peak values of 16.0 .+-. 3.8 (10 nM), 23.1 .+-. 3.9 (1 .mu.M) and 28.1 .+-. 4.9 (10 .mu.M) .times. 10-6 cm s-1 (n = 24). In 10 other monolayers, after the addition of 1 mM 8-Br-cAMP, urea permeability increased from 5.1 .+-. 0.3 to 8.1 .+-. 1.6 .times. 10-6 cm s-1 and, after 8-Br-cAMP + 3-isobutyl-1-methylxanthine, to 12.2 .+-. 0.7 .times. 10-6 cm s-1. We conclude that rat IMCD cells grown in culture exhibit the characteristics of a ''tight'' epithelium. Inulin and urea permeability are not different in the absence of AVP, consistent with high resistance junctional complexes, Furthermore, IMCD cells retain the capacity of AVP-regulated urea permeability, a characteristic feature of this nephron segment in vivo.