Calcium signaling in rat pancreatic acinar cells: a role for Galphaq, Galpha11, and Galpha14.

Abstract

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 alpha-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 Galphaq, Galpha11, and Galpha14 but were not amplified with primers specific for Galpha15. The sequences of these PCR products confirmed them to be portions of the rat homologues of Galphaq, Galpha11, and Galpha14. The pancreatic-derived cell line AR42J similarly expressed Galphaq, Galpha11, and Galpha14; however, the Chinese hamster ovary (CHO) cell line only expressed Galpha11 and Galphaq. 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 alpha-subunits. The role of these proteins in Ca2+ signaling events was investigated by microinjecting a neutralizing antibody directed against a homologous sequence in Galphaq, Galpha11, and Galpha14 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 Galphaq and/or Galpha11 in intracellular Ca2+ concentration signaling in CHO cells, and in addition to Galphaq and Galpha11, Galpha14 may also fulfill this role in rat pancreatic acinar cells.