Fig. 3: DOP inhibition activates insulin secretion from human beta cells and islets.

(A) Insulin secretion was assessed in EndoCβH5 cells treated with no glucose (green; LG) either with 10 μM NTI (n = 10 independent cell preparations), 5 μM DII (n = 12), a combination of both (n = 12) or no treatment (n = 12), for 40 min. (B) Insulin secretion was assessed in EndoCβH5 cells treated with 20 mM glucose (violet; HG) supplemented with 10 μM NTI (n = 10), 5 μM DII (n = 12), a combination of both (n = 12) or no treatment (n = 11), for 40 min. (C) Insulin secretion was assessed in human islets treated with 2.8 mM glucose (green; LG) supplemented with 10 μM NTI (n = 24 single isolated islets), 5 μM DII (n = 24), a combination of both (n = 29), or no treatment (n = 28), for 120 min. (D) Insulin secretion was assessed in human islets treated with 16.7 mM glucose (violet; HG) supplemented with 10 μM NTI (n = 23), 5 μM DII (n = 24), a combination of both (n = 29) or no treatment (n = 28), for 120 min. Data are box plots (showing the minimum, the median, the maximum, as well as all data). P-values are shown relative to control by unpaired two-tailed Mann-Whitney test. DII, [D-Ala2]-Deltorphin II; HG, high glucose; LG, low glucose; ns, not significant; NTI, naltrindole.