Protein kinase A increases the binding affinity and the Ca2+ release activity of the inositol 1,4,5-trisphosphate receptor type 3 in RINm5F cells.

BACKGROUND INFORMATION

In endocrine cells, IP(3)R (inositol 1,4,5-trisphosphate receptor), a ligand-gated Ca2+ channel, plays an important role in the control of intracellular Ca2+ concentration. There are three subtypes of IP(3)R that are distributed differentially among cell types. RINm5F cells express almost exclusively the IP(3)R-3 subtype. The purpose of the present study was to investigate the effect of PKA (protein kinase A) on the activity of IP(3)R-3 in RINm5F cells.

RESULTS

We show that immunoprecipitated IP(3)R-3 is a good substrate for PKA. Using a back-phosphorylation approach, we show that endogenous PKA phosphorylates IP(3)R-3 in intact RINm5F cells. [(3)H]IP(3) (inositol 1,4,5-trisphosphate) binding affinity and IP(3)-induced Ca2+ release activity were enhanced in permeabilized cells that were pre-treated with forskolin or PKA. The PKA-induced enhancement of IP(3)R-3 activity was also observed in intact RINm5F cells stimulated with carbachol and epidermal growth factor, two agonists that use different receptor types to activate phospholipase C.

CONCLUSION

The results of the present study reveal a converging step where the cAMP and the Ca2+ signalling systems act co-operatively in endocrine cell responses to external stimuli.