Urea flux across MDCK-mUT-A2 monolayers is acutely sensitive to AVP, cAMP, and [Ca2+]i

In this study, we engineered a Madin-Darby canine kidney (MDCK) type I cell line to stably express the mouse urea transporter UT-A2. Monolayers of MDCK-mUT-A2 cells had a basal phloretin-inhibitable urea permeability of 8.4x10(-6)+/-0.3 cm/s. Treatment of MDCK-mUT-A2 monolayers with AVP led to a rapid dose-dependent increase in trans-monolayer phloretin-inhibitable urea flux. The temporal pattern of response was markedly different from that observed for MDCK cells expressing rat UT-A1. Exposure of MDCK-mUT-A2 cells to either 10 microM forskolin or 250 microM 8-bromo cAMP also increased urea flux rate. Inclusion of the PKA inhibitor H89 (10 microM) had no effect on the forskolin-stimulated increase in urea flux across MDCK-mUT-A2 monolayers. Treatment with either 10 microM CPA or 1 mM ATP also caused an increase in UT-A2-mediated urea flux, although these responses where transient compared with those induced by AVP or elevated cAMP. Taken together, these results show for the first time that UT-A2 is acutely sensitive to AVP, cAMP, or increased intracellular calcium.