IMMUNOCYTOCHEMICAL LOCALIZATION OF THE GTP-BINDING PROTEIN G(0)-ALPHAIN THE VESTIBULAR EPITHELIUM AND GANGLION OF THE GUINEA-PIG

The guanine nucleotide binding protein Go alpha was immunolocalized in the guinea-pig vestibular system by confocal and electron microscopy. The vestibular sensory epithelia consist of the macula utriculi, macu la sacculi and cristae ampullaris of the semicircular canals. Two type s of hair cells are present in these epithelia. Type I hair cells are surrounded by an afferent nerve calyx that receives efferent innervati on and type IT hair cells are innervated directly by the afferent and efferent nerves. Go alpha protein was observed on the inner face of th e afferent calyceal membrane surrounding type I hair cells and in nerv e endings in contact with type II hair cells. No labelling was found i n the stereocilia and cuticular plate of type I and type II hair cells whereas the cytoplasmic matrix displayed a diffuse labelling. The pla sma membrane of the supporting cells showed discreet labelling in the confocal microscope that are still confirmed by electron microscopy. A positive reaction was also observed along the plasma membrane of the vestibular ganglion neurons. Immunoblotting with affinity-purified pol yclonal rabbit antibodies selective for the 39 kDa alpha subunit of G( o) indicated that G(o) alpha protein was present in both the vestibula r ganglion. That G(o) alpha labelling was observed in the cytoplasm of vestibular hair cells and in nerve endings contacting hair cells sugg ests that G(o) may be involved in the modulation of vestibular neurotr ansmission.