Figure 5.

Requirement of Glutamate Transport into Insulin Granules for Amplification of Insulin Secretion by Incretin/cAMP Signaling

(A) mRNA expression levels of VGLUTs in MIN6-K8 cells (n = 3–4 for each). n.d., not detected.

(B) Immunocytochemical analysis of VGLUT1 in MIN6-K8 cells and pancreatic islets. Scale bars, 10 μm.

(C) Immunoblot analysis of VGLUT1 in insulin granules in MIN6-K8 cells. The insulin granule fraction was confirmed by immunoblot analysis using anti-PC1/3 antibody.

(D) Effect of Evans blue, an inhibitor of vesicular glutamate transport, on insulin secretion from MIN6-K8 cells (n = 5–8 for each).

(E and F) Effects of KD of VGLUT1 (E) and VGLUT2 (F) on insulin secretion from MIN6-K8 cells (n = 4–8 for each).

(G) Insulin secretion from pancreatic islets of wild-type (Slc17a7^+/+) and VGLUT1 knockout (Slc17a7^−/−) mice (n = 4–8 for each). dm-glutamate, dimethyl-glutamate.

(H) Effect of KD of V-ATPase subunit D on insulin secretion from MIN6-K8 cells (n = 4 for each).

(I) Effect of bafilomycin, an inhibitor of V-ATPase, on insulin secretion from MIN6-K8 cells (n = 4 for each).

The data are expressed as means ± SEM. Results are representative of three independent experiments. Welch’s t test (D–F, H, and I) and Dunnett’s method (G) were used for evaluation of statistical significance. ^∗p < 0.05; ^∗∗p < 0.01; n.s., not significant. See also Figure S5.