This has been done multiple times using western blotting using antibodies recognizing either all AQP2 or only phosphorylated fractions of the total pool. Differential centrifugation can be used to separate AQP2 in the plasma-membrane from AQP2 in intracellular vesicles. Immuno-electron microscopy can also be used to quantify AQP2, and even fluorescence microscopy can be done in a quantitative way using again antibodies.

Just a few references:

(1) Ecelbarger, C. A.; Terris, J.; Frindt, G.; Echevarria, M.; Marples, D.; Nielsen, S.; Knepper, M. A. Aquaporin-3 Water Channel Localization and Regulation in Rat Kidney. Am J Physiol 1995, 269, F663–F672.

(1) DiGiovanni, S. R.; Nielsen, S.; Christensen, E. I.; Knepper, M. A. Regulation of Collecting Duct Water Channel Expression by Vasopressin in Brattleboro Rat. Proc Natl Acad Sci USA 1994, 91, 8984–8988.

(1) Kamsteeg, E. J.; Heijnen, I.; van Os, C. H.; Deen, P. M. The Subcellular Localization of an Aquaporin-2 Tetramer Depends on the Stoichiometry of Phosphorylated and Nonphosphorylated Monomers. J Cell Biol 2000, 151, 919–930.

(1) Nielsen, S.; Chou, C. L.; Marples, D.; Christensen, E. I.; Kishore, B. K.; Knepper, M. A. Vasopressin Increases Water Permeability of Kidney Collecting Duct by Inducing Translocation of Aquaporin-CD Water Channels to Plasma Membrane. Proc Natl Acad Sci USA 1995, 92, 1013–1017.

Thank you very much!  The literature has been very helpful!

Cheer

PA