Transduction Proteins of Olfactory Receptor Cells: Identification of Guanine Nucleotide Binding Proteins and Protein Kinase C

We have analyzed guanine nucleotide binding proteins (G-proteins) in the olfactory epithelium of Rana catesbeiana using subunit-specific antisera. The olfactory epithelium contained the a subunits of three G-proteins, migrating on polyacrylamide gels in SDS with apparent molecular weights of 45 000, 42 000, and 40 000, corresponding to G_s, G_j, and G_o, respectively. A single β subunit with an apparent molecular weight of 36000 was detected. An antiserum against the α subunit of retinal transducin failed to detect immunoreactive proteins in olfactory cilia detached from the epithelium. The olfactory cilia appeared to be enriched in immunoreactive G_sα relative to G_iα and G_oα when compared to membranes prepared from the olfactory epithelium after detachment of the cilia, α subunits of G-proteins were not detected in cilia detached from the nonchemosensory respiratory epithelium of the palate. Immunohistochemical studies using an antiserum against the β subunit of G-proteins revealed intense staining of the ciliary surface of the olfactory epithelium and of the axon bundles in the lamina propria. In contrast, an antiserum against a common sequence of the α subunits preferentially stained the cell membranes of the olfactory receptor cells and the acinar cells of Bowman’s glands and the deep submucosal glands. Prolonged incubation periods with these antisera tended to obliterate these differences in staining patterns, giving rise to staining by both antisera of the ciliary surface, the olfactory receptor cell membranes, the axon bundles, and the acinar cells of the glands. In addition to G-proteins, we have identified protein kinase C in olfactory cilia via a protein kinase C specific antiserum and via phorbol ester binding. However, in contrast to the G-proteins, protein kinase C occurred also in cilia isolated from respiratory epithelium.