AJP - Cell Physiology, Vol 263, Issue 6 C1225-C1233, Copyright © 1992 by American Physiological Society
Localization of the CHIP28 water channel in rat kidney
I. Sabolic, G. Valenti, J. M. Verbavatz, A. N. Van Hoek, A. S. Verkman, D. A. Ausiello and D. Brown
Renal Unit, Massachusetts General Hospital, Boston.
CHIP28 is an integral membrane protein that has been identified as the
erythrocyte water channel and that is also expressed in the kidney.
Antibodies against erythrocyte CHIP28 were used to localize this protein
along the rat urinary tubule. By Western blotting, CHIP28 was detected in
kidney plasma membrane and endosome fractions. With the use of
immunocytochemistry, CHIP28 was located in brush-border and basolateral
plasma membranes of the proximal tubule. The initial S1 segment was weakly
stained, but the S2 and S3 segments were heavily labeled. Subapical
vesicles were also positive. Apical and basolateral membranes of the long
thin descending limb were strongly labeled, but ascending thin and thick
limbs of Henle and distal convoluted tubules were negative. Some vasa recta
profiles in the medulla were positive. CHIP28 is, therefore, present in
membranes with a high constitutive water permeability, where it probably
acts as a transmembrane water-conducting channel. Finally, a weak staining
of apical and basolateral membranes of cortical collecting duct principal
cells was detectable, suggesting a potential relationship of CHIP28 to the
vasopressin-sensitive water channel.
