Abstract
Glucagon induces intracellular Ca2+ ([Ca2+]i) elevation by stimulating glucagon receptor (GCGR). Such [Ca2+]i signaling plays important physiological roles, including glycogenolysis and glycolysis in liver cells and the survival of β-cells. Previous studies indicated that phospholipase C (PLC) might be involved in glucagon-mediated [Ca2+]i response. Other studies also debated whether cAMP accumulation mediated by GCGR/Gαs coupling contributes to [Ca2+]i elevation. But the exact mechanisms remain uncertain. In the present study, we found that glucagon induces [Ca2+]i elevation in HEK293 cells expressing GCGR. Removing extracellular Ca2+ did not affect glucagon-stimulated [Ca2+]i response. But depleting the intracellular Ca2+ store by thapsigargin completely inhibited glucagon-induced [Ca2+]i response. Experiments with forskolin and adenylyl cyclase inhibtor revealed that cAMP is not the cause of [Ca2+]i response. Further studies with Gαq/11 RNAi and pertussis toxin (PTX) indicated that both Gαq/11 and Gαi/o are involved. Combination of Gαq/11 RNAi and Gαi/o inhibition almost completely abolished glucagon-induced [Ca2+]i signaling.
Acknowledgements
This work was supported by grants from the National Natural Sciences Foundation of China (90713047), Ministry of Science and Technology of China (2007AA02Z308,2009CB940900), and Shanghai Commission of Science and Technology (08JC1407701,09DZ2291200).
Declaration of interest: The authors declare no conflict of interest.