Stimulus-secretion coupling in the pancreatic acinar cell is initiated by the secretagogues CCK and ACh and results in the secretion by exocytosis of the contents of zymogen granules. A key event in this pathway is the G protein-activated production of second messengers and the subsequent elevation of cytosolic-free Ca2+. The aim of this study was therefore to define the heterotrimeric G protein α-subunits present and participating in this pathway in rat pancreatic acinar cells. RT-PCR products were amplified from pancreatic acinar cell mRNA with primers specific for Gαq, Gα11, and Gα14 but were not amplified with primers specific for Gα15. The sequences of these PCR products confirmed them to be portions of the rat homologues of Gαq, Gα11, and Gα14. The pancreatic-derived cell line AR42J similarly expressed Gαq, Gα11, and Gα14; however, the Chinese hamster ovary (CHO) cell line only expressed Gα11 and Gαq. These data indicate that caution should be exercised when comparing signal transduction pathways between different cell types. The expression of these proteins in acinar cells was confirmed by immunoblotting samples of acinar membrane protein using specific antisera to the individual G protein α-subunits. The role of these proteins in Ca2+ signaling events was investigated by microinjecting a neutralizing antibody directed against a homologous sequence in Gαq, Gα11, and Gα14 into acinar cells and CHO cells. Ca2+ signaling was inhibited in acinar cells and receptor-bearing CHO cells in response to both physiological and supermaximal concentrations of agonists. The inhibition was >75% in both cell types. These data indicate a role for Gαq and/or Gα11 in intracellular Ca2+ concentration signaling in CHO cells, and in addition to Gαq and Gα11, Gα14 may also fulfill this role in rat pancreatic acinar cells.
Genes for two homologous G-protein α subunits map to different human chromosomes
