Localization of the G-protein G(o) in exocrine glands.

The GTP-binding protein G(o) was localized immunohistochemically in the rat parotid gland and in other exocrine glands with specific G(o) antibodies. Immunohistochemical studies revealed that affinity-purified G(o alpha) polyclonal antibody (GO/85) immunoreacted primarily with duct cells of the rat parotid gland; immunoreactivity was also noted in duct cells of the rat submandibular, mouse parotid, and mouse submandibular glands. Light labeling of rat parotid and submandibular gland acinar cells was also noted. G(o alpha) antiserum (9072) differing in specificity for epitopes within G(o alpha) produced similar results. This antiserum also immunoreacted with rat submandibular duct cell secretory granule membranes. In contrast, in rat and mouse pancreas G(o alpha) antibodies immunoreacted primarily with islet cells. Duct cells were negative but there was light labeling of rat pancreatic acinar cells. The apparent duct specificity of G(o alpha) staining was further verified by demonstrating that G(o alpha) antibodies immunoreacted with HSG-PA cells, a human transformed salivary duct cell line. Specificity in immunohistochemical labeling of HSG-PA cells was confirmed by Western blot analysis. The results demonstrate that G(o) appears to be selectively expressed in the duct cells of rat parotid gland and other salivary glands. The selective enrichment of G(o) in duct cells suggests that this G-protein plays an important role in duct cell physiology.