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Published ahead of print on January 12, 2005
J Am Soc Nephrol 16: 600-607, 2005
© 2005 American Society of Nephrology
doi: 10.1681/ASN.2004030241
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Cell and Transport Physiology

Modulation of Hypertonicity-Induced Aquaporin-1 by Sodium Chloride, Urea, Betaine, and Heat Shock in Murine Renal Medullary Cells

Fuminori Umenishi*,{dagger}, Shigemi Yoshihara{ddagger}, Takefumi Narikiyo* and Robert W. Schrier*

* Department of Medicine and {dagger} Department of Physiology and Biophysics, University of Colorado Health Sciences Center, Denver, Colorado; and {ddagger} Department of Pediatrics, Dokkyo University School of Medicine, Tochigi, Japan

Address correspondence to: Dr. Fuminori Umenishi, Division of Renal Diseases and Hypertension, Department of Medicine, University of Colorado Health Sciences Center, 4200 East Ninth Avenue, Box C281, Denver, CO 80262. Phone: 303-315-6715; Fax: 303-315-4852; E-mail: fuminori.umenishi{at}uchsc.edu

Aquaporin-1 (AQP1) expression is induced by hypertonicity in renal medullary cells. The purpose of the present study was to elucidate the role of sodium chloride (NaCl), urea, betaine, and heat shock on hypertonicity-induced AQP1 expression in cultured murine renal medullary-K2 (mIMCD-K2) cells. AQP1 expression was maximally induced under mild hypertonic medium supplemented with 100 mM NaCl (N100), whereas severe hypertonic medium supplemented with 150 mM NaCl (N150) caused little AQP1 induction. The reduction of AQP1 expression in N150 was associated with reduced cell viability. When cells were exposed continuously to N100, hypertonicity-induced AQP1 expression was elevated, whereas the return to isotonic medium reduced AQP1 expression in a time-dependent manner. The half-life of AQP1 protein in isotonic conditions was approximately 4 h, whereas hypertonicity markedly increased its half-life. These results indicate that hypertonicity plays an important role in AQP1 induction, stability, and degradation. On the contrary, urea inhibited hypertonicity-induced AQP1 expression in a dose-dependent manner. The addition of organic osmolyte betaine in N150 enhanced hypertonicity-induced AQP1 expression, whereas it decreased AQP1 expression in N100. This suggests that the excessive accumulation of betaine may counteract hypertonic stress and thus attenuate hypertonicity-induced AQP1 expression. Heat shock treatment promoted hypertonicity-induced AQP1 and heat shock protein 70 (HSP70) expression in both N100 and N150, suggesting an effect on the stability of hypertonicity-induced AQP1 expression. Taken together, NaCl, urea, betaine, and heat shock that regulate hypertonicity-induced AQP1 expression are potentially important factors in urinary concentration and contribute to the steady-state level of AQP1 expression.


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