Fig. 4.

PKA phosphorylation at sites S486 and S499 is needed for urea transport activity in Xenopus oocytes. Oocytes were injected with indicated cRNA or a mixture of cRNAs as described in methods. A: before urea flux was measured, oocytes were incubated in the absence (open bars) or presence (filled bars) of 500 μM 8-(4-chlorophenylthio)-adenosine-3′,5′-cyclic monophosphate (CPT-cAMP), 500 μM 3-isobutyl-1-methylxanthine (IBMX), and 50 μM forskolin for 2 h. Each bar shows the mean ± SE obtained from 6 individual oocytes from 3 different experiments. *P < 0.05. B: representative Western blot analysis shows equal expression of wild-type UT-A1 and each of the UT-A1 mutant proteins generated by oocytes.