Tohoku J. Exp. Med., 2002, 197 (2)

Ultrastructural Localization of Aquaporin 4 and a1-Syntrophin
in the Vascular Feet of Brain Astrocytes

MASAHIKO INOUE, YOSHIHIRO WAKAYAMA, JIAN WU LIU, MAKOTO MURAHASHI,
SEIJI SHIBUYA and HIROAKI ONIKI¹

Department of Neurology, and ¹Electron Microscope Laboratory,
Showa University Fujigaoka Hospital, Yokohama 227-8501

Aquaporin 4 (AQP4) is a recently discovered membrane bound water-selective channel and has been described at the light microscopic level to be predominantly expressed in the astrocytes of the brain, especially at the perivascular astrocyte endfoot processes. a1-Syntrophin, a member of dystrophin-associated protein, has also been reported at the light microscopic to be expressed level in the same site of astrocytes as AQP4 and interacts with other molecules through its PDZ domain. AQP4 expression has been reported to be absent at the sarcolemma and the perivascular astrocyte endfoot processes of a1-syntrophin knockout mice. Based on these observations, the molecular association between AQP4 and a1-syntrophin could be speculated. To test this hypothesis, we investigated the ultrasturctural localization of AQP4 and a1-syntrophin in the brain astrocytes by using double immunogold labeled electron microscopy. The results showed that AQP4 and a1-syntrophin colocalized frequently at the astrocyte membrane, especially at the perivascular astrocyte endfoot processes and suggested the presence of linkage between AQP4 and a1-syntrophin at the astrocyte plasma membrane.

Keywords —— aquaporin 4; a1-syntrophin; double immunogold electron microscopy; colocalization; astrocyte endfoot

© 2002 Tohoku University Medical Press

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Tohoku J. Exp. Med., 2002, 197, 87-93

Address for reprints: Yoshihiro Wakayama, M.D., Ph.D., Department of Neurology, Showa University Fujigaoka Hospital, 1-30 Fujigaoka, Aoba-ku, Yokohama 227-8501, Japan.

e-mail: inoue834@dc.mbn.or.jp