| Research Abstract |
1) Cloning of water channels (AQPs)
We cloned the following AQPs ; AQP7 from rat testis that has permeability to glycerol and urea in addition to water, AQP8 from rat testis that is water-selective, AQP9 from human leukocyte that has permeability to urea in addition to water, and AQP9L, a homologue of AQP9, from rat liver.
2) Determination of AQP structure
a. We identified mercury-sensitive cystein in human AQP3 and showed evidence suggesting that water, glycerol, and urea share a common pore.
b. AQP family is divided into two groups ; MIP group that is water-selective and glpF group that is permeable to small molecules. Only the latter group possesses two portions which are composed of about 15 amino acid. We examined the significance of these portions and found the portions are not associated with channel selectivity.
c. AQP2 and MIP are highly homologous (58% amino acid homology), whereas the water permeability of AQP2 is much higher than that of MIP. We constructed chimera proteins of AQP2 and MIP and determined several amino acids in transmembrane helix5 is responsible for the high water permeability of AQP.
3. Intracellular mechanisms and signal transduction related to urinary concentration
a. A short or a long time exposure to high osmolality decreased the activity of Na-K-ATPase in rat inner medullary collecting duct cells. We found that the mechanism of Na-K-ATPase inhibition was different in the short and long time exposure.
b. We investigated signal transduction pathways in LLC-PK1 and mesangial cells and obtained several new findings.
4. Pathogenesis of nephrogenic diabetes insipidus (NDI)
a. We characterized T125M and G175R, AOP2 mutants found in autosomal recessive NDI, and found the decrease of the water channel function of these mutants.
b. We characterized 809del 7, and AQP2 mutant found in autosomal dominant NDI, and found that this mutation causes the inhibition of transcription or the defect of protein trafficking.
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