Phosphorylation of both UT-A1 and UT-A3 is blocked by an inhibitor of PKA. (A) Rat IMCD samples were treated with either vehicle, the PKA inhibitor H89, or the MEK inhibitor U0126 for 10 minutes, followed by incubation with dDAVP for 20 minutes, followed by immunoblotting with antibodies to AQP2 Ser(p)-256, UT-A1 and UT-A3 Ser(p)-84, UT-A1 Ser(p)-486, total UT-A1 and UT-A3, and pERK. (B to F) Quantification of band densities from these immunoblots as well as other trials (n = 3; *P < 0.05 versus vehicle; ***P < 0.001 versus vehicle).