FIGURE 7.

N55 specifically enhances GLP-1(7–36)-amide-stimulated cAMP production in RINm5F cells. A, effect of increasing concentrations of N55 on cAMP production in response to GLP-1(7–36)-amide titration in RINm5F cells expressing RG-cAMP biosensor. B, N55 dose-dependently and saturably increases the potency of GLP-1 to stimulate cAMP production. C, effect of exendin 9 on cAMP production in response to 150 pm GLP-1(7–36)-amide alone or together with the presence of 7.7 μm N55. Effect of N55 on cAMP production responses to the titrations of Ex-4 (D) or GIP (E). Activity was expressed as cAMP production % of the maximal response and was calculated as 100×(A − B)/(A − M), where A = BRET ratio by 10 pm GLP-1(7–36)-amide; B = BRET ratio by indicated concentration of GLP-1(7–36)-amide in the presence of indicated concentration of N55, and M = BRET ratio by 0.25 μm GLP-1(7–36)-amide. Increase in potency of GLP-1 to stimulate cAMP response is calculated by (EC₅₀ of GLP-1)/(EC₅₀ of GLP-1 in the presence of indicated concentration of N55). Data are mean ± S.E. of triplicates of three independent experiments. Student's t test (p < 0.001) for cAMP response elicited by 150 pm GLP-1(7–36) in the absence versus the presence of N55.