Immunohistochemical localization of G protein βγ subunits in the lateral wall of the rat cochlea

The role of G protein-mediated signal transduction in the production of endolymph, an extracellular fluid of unusual ionic composition, is beginning to be understood. The identity of Gα subunits in the stria vascularis and the spiral ligament of the lateral wall of the cochlear duct is well established. However, little is known about the presence of βγ subunits. This study used immunohistochemistry to investigate the distribution of G protein βγ subunits in the lateral wall of the cochlea. Temporal bones of 6- to 8-week-old rats were fixed in 4% paraformaldehyde and 0.1% glutaraldehyde and processed for embedding in paraffin wax. The dewaxed, midmodiolar sections of the cochlea were incubated with subunit-specific polyclonal antibodies. The results show that the pattern of immunoreactivity varies for the G protein β1-4 and γ1-3, 5 and 7 subunits in the stria vascularis and spiral ligament. In the stria vascularis, immunoreactivity was detected for β2, β3, β4, γ1, γ2 and γ7 subunits. All five types of fibrocytes in the spiral ligament exhibited positive staining for γ2 and γ7. However, immunoreactivity for β1-4 subunits was variable. Immunoreactivity for γ3 and γ5 subunits was not detected in the lateral cochlear wall. The expression pattern of G protein βγ subunits in lateral wall provides a basis for interpreting the functions of G protein-coupled receptors in cochlear fluid homeostasis.