Calcium signaling in rat pancreatic acinar cells: a role for G alpha(q),, G alpha(11), and G alpha(14)

Stimulus-secretion coupling in the pancreatic acinar cell is initiated by t he 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 prot ein-activated production of second messengers and the subsequent elevation of cytosolic-free Ca2+. The aim of this study was therefore to define the h eterotrimeric G protein alpha-subunits present and participating in this pa thway in rat pancreatic acinar cells. RT-PCR products were amplified from p ancreatic acinar cell mRNA with primers specific for G alpha(q), G alpha(11 ), and G alpha(14) but were not amplified with primers specific for G alpha (15). The sequences of these PCR products confirmed them to be portions of the rat homologues of Gee,, Gall, and G alpha(14) The pancreatic-derived ce ll line AR42J similarly expressed G alpha(q), G alpha(11), and G alpha(14); however, the Chinese hamster ovary (CHO) cell line only expressed G alpha( 11) and G alpha(q). These data indicate that caution should be exercised wh en comparing signal transduction pathways between different cell types. The expression of these proteins in acinar cells was confirmed by immunoblotti ng samples of acinar membrane protein using specific antisera to the indivi dual G protein a-subunits. The role of these proteins in Ca2+ signaling eve nts was investigated by microinjecting a neutralizing antibody directed aga inst a homologous sequence in G alpha(q), G alpha(11), and G alpha(14) into acinar cells and CHO cells. Ca2+ signaling was inhibited in acinar cells a nd receptor-bearing CHO cells in response to both physiological and superma ximal concentrations of agonists. The inhibition was >75% in both cell type s. These data indicate a role for G alpha(q) and/or Gall in intracellular C a2+ concentration signaling in CHO cells, and in addition to G alpha(q) and G alpha(11), G alpha(14) may also fulfill this role in rat pancreatic acin ar cells.