LOCALIZATION OF A G-PROTEIN G(I2) IN THE CILIA OF RAT EPENDYMA, OVIDUCT AND TRACHEA

In previous studies, the localization of a pertussis toxin-sensitive G protein was demonstrated in ependymal cilia, but the identification o f the subtype of G protein was inconsistent. To clarify this issue, we studied the localization of G(o) alpha, G(i1)alpha, G(i3)alpha and G( i2)alpha in the ciliated ependymal cells and in the cilia of some othe r tissues of rats using specific antibodies. The cilia of the ependyma l cells that line the ventricular cavity of the brain were intensely i mmunoreactive for G(i2)alpha, but not for G(o) alpha, G(i1)alpha or G( i3)alpha. Immunoblot analysis demonstrated higher levels of G(i2)alpha in the ependymal cilia-rich pellet than in the motor area of the pari etal cortex. At the ultrastructural level, the immunoreactivity specif ic for G(i2)alpha was found predominantly in the cilia, but rarely in the microvilli or the basal bodies of ependymal cells. In cross-sectio ns, the immunoreactivity specific for G(i2)alpha was observed only in cell membranes, in particular, in the inner electron-dense leaflet of the trilaminar structure. In addition to that in the ependymal cilia, such specific localization of G(i2)alpha was observed in the motile ci lia in other tissues, including the oviduct and trachea. By contrast, the stereocilia in the ductus deferens were not immunopositive for G(i 2)alpha. These findings suggest that G(i2) might play an important rol e in the signal transduction in ciliary membrane-associated function(s ) of the ependymal cells, oviduct and trachea.