IDENTIFICATION AND LOCALIZATION OF G-PROTEINS IN EXOCRINE GLANDS

GTP-binding proteins were identified in rat parotid acinar plasma-enri ched membranes (PM) by immunoblot analysis and localized immunohistoch emically in the parotid gland as well as in other exocrine glands by u sing affinity-purified antisera specific for alpha subunits of the G p roteins. Isolated rat parotid acinar PM immunoreacted strongly to anti sera directed against Gsalpha, Gialpha1/alpha2, Gialpha3, and Goalpha; the signal for Goalpha, however, was weak with crude Go antisera. Imm unohistochemical studies to identify and localize Go in rat parotid ti ssue revealed that antisera to Goalpha immunoreacted with ductal cells . In addition, strong immunoreactivity to Goalpha antisera was noted i n ductal cells of other salivary glands including rat submandibular, m ouse parotid, and mouse submandibular glands. Light labeling of rat pa rotid and submandibular gland acinar cells was also noted. In contrast , in the rat and mouse pancreas, Go antisera immunoreacted primarily w ith islet cells. Ductal cells were negative, but there was light label ing of rat pancreatic acinar cells. The apparent ductal specificity of Goalpha staining was further verified by demonstrating that Goalpha a ntisera immunoreacted strongly with HSG-PA cells, a human transformed salivary ductal cell line. The results demonstrate that rat parotid ac inar plasma membranes express a number of G proteins including Go and that Go appears to be selectively expressed in the ductal cells of rat parotid gland and other salivary glands. The selective enrichment of Go in ductal cells suggests that this G protein may play an important role in ductal cell physiology.