Vasopressin-regulated water permeability of the kidney collecting duct is a key component of the urine concentration machinery. Recently, a cDNA for AQP-CD, the vasopressin-regulated water channel, initially reported as WCH- CD has been isolated (K. Fushimi, S. Uchida, Y. Hara, Y. Hirata, F. Marumo, and S. Sasaki, Nature Lond. 361:549-552, 1993). AQP-CD was expressed in oocyte membrane using a Xenopus expression vector, and functional characteristics of AQP-CD were examined. Osmotic water permeability (P(f)) of oocytes expressing AQP-CD was 138 ± 19 μm/s (mean ± SE), 12 times greater than the control (11 ± 3 μm/s), 90% inhibited by 0.3 mM HgCl2, and weakly temperature dependent (energy of activation for P(f) was 4.0 kcal/mol). Urea influx measured from 15-min [14C]urea uptake by oocytes injected with AQP- CD/expression vector 1 cRNA was 86 ± 17% of the control. Two-electrode voltage-clamp experiments revealed insignificant ion conductance of AQP-CD. Immunoblots of membranes from rat kidney medulla and oocytes expressing AQP- CD using anti-AQP-CD COOH-terminal antibody showed a 29-kDa protein and 35- to 50-kDa high-molecular-mass forms. Immunohistochemistry showed apical and subapical localization of AQP-CD in the collecting duct principal cells. Our results indicated that AQP-CD is a 29-kDa protein, a selective water channel, distinct from a urea channel, and localized to the membranes of vasopressin- sensitive components in kidney collecting duct principal cells.
|ジャーナル||American Journal of Physiology - Renal Fluid and Electrolyte Physiology|
|出版ステータス||Published - 1994|
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