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Am J Physiol Renal Physiol 277: F734-F741, 1999;
0363-6127/99 $5.00
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Vol. 277, Issue 5, F734-F741, November 1999

Functional analysis of aquaporin-2 mutants associated with nephrogenic diabetes insipidus by yeast expression

Itsuki Shinbo1,2, Kiyohide Fushimi1,3, Michihiro Kasahara4, Kazushi Yamauchi1, Sei Sasaki1, and Fumiaki Marumo1

1 Second Department of Internal Medicine, 2 Department of Physiology, and 3 Department of Medical Informatics, Tokyo Medical and Dental University School of Medicine, and 4 Laboratory of Biophysics, School of Medicine, Teikyo University, Tokyo 113-8519, Japan

Mutations of aquaporin-2 (AQP2) vasopressin water channel cause nephrogenic diabetes insipidus (NDI). It has been suggested that impaired routing of AQP2 mutants to the plasma membrane causes the disease; however, no determinations have been made of mutation-induced alterations of AQP2 channel water permeability. To address this issue, a series of AQP2 mutants were expressed in yeast, and the osmotic water permeability (Pf) of the isolated vesicles was measured. Wild-type and mutant AQP2 were expressed equally well in vesicles. Pf of the vesicles containing wild-type AQP2 was 22 times greater than that of the control, which was sensitive to mercury and weakly dependent on the temperature. Pf measurements and mercury inhibition examinations suggested that mutants L22V and P262L are fully functional, whereas mutants N68S, R187C, and S216P are partially functional. In contrast, mutants N123D, T125M, T126M, A147T, and C181W had very low water permeability. Our results suggest that the structure between the third and fifth hydrophilic loops is critical for the functional integrity of the AQP2 water channel and that disruption of AQP2 water permeability by mutations may cause NDI.

water channel; vasopressin


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