K. Fushimi is the first author of the 1993 study that cloned and functionally tested the kidney water channel now known as aquaporin-2. The team localized it to the collecting duct and expressed its sequence in Xenopus oocytes, connecting a candidate membrane protein to measured water transport.[ref]
Cloning and expression of apical membrane water channel of rat kidney collecting tubule by K. Fushimi and others. byline and abstract, localization and functional expression
A 1997 first-authored study tested how that channel reaches the cell membrane. The investigators replaced serine256 with alanine and compared the resulting protein with the normal sequence in cultured cells. A stopped-flow light-scattering assay measured osmotic water permeability, while surface labeling assessed membrane localization. cAMP stimulation increased permeability by about for the normal construct but only about for the altered construct in the reported experiments.[ref]
Phosphorylation of serine 256 is required for cAMP-dependent regulatory exocytosis of the aquaporin-2 water channel by K. Fushimi and others. abstract, S256A comparison and measured cAMP responses
The comparison links phosphorylation at a defined amino-acid position to regulated exocytosis and membrane water transport. It also separates two questions: can a protein transport water, and can a cell adjust how much of that protein is present at its surface?
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