cAMP‐dependent protein kinase enhances inositol 1,4,5‐trisphosphate‐induced Ca 2+ release in AR4‐2J cells

In non‐excitable cells, the inositol 1,4,5‐trisphosphate receptor (IP 3 R), a ligand‐gated Ca 2+ channel, plays an important role in the control of intracellular Ca 2+ . There are three subtypes of IP 3 R that are differentially distributed among cell types. AR4‐2J cells express almost exclusively the IP 3 R‐2 subtype. The purpose of this study was to investigate the effect of cAMP‐dependent protein kinase (PKA) on the activity of IP 3 R‐2 in AR4‐2J cells. We showed that immunoprecipitated IP 3 R‐2 is a good substrate for PKA. Using a back‐phosphorylation approach, we showed that endogenous PKA phosphorylates IP 3 R‐2 in intact AR4‐2J cells. Pretreatment with PKA enhanced IP 3 ‐induced Ca 2+ release in permeabilized AR4‐2J cells. Pretreatment with the cAMP generating agent's forskolin and vasoactive intestinal peptide (VIP) enhanced carbachol (Cch)‐induced and epidermal growth factor (EGF)‐induced Ca 2+ responses in intact AR4‐2J cells. Our results are consistent with an enhancing effect of PKA on IP 3 R‐2 activity. This conclusion supports the emerging concept of crosstalk between Ca 2+ signaling and cAMP pathways and thus provides another way by which Ca 2+ signals are finely encoded within non‐excitable cells. J. Cell. Biochem. 101: 609–618, 2007. © 2007 Wiley‐Liss, Inc.