Regulation of glucose-stimulated cAMP by PDEs in human pancreatic β-cells.
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A-C) Subtype-selective PDE inhibitors and IBMX raise cAMP levels in pancreatic β-cells dissociated from human islets under high glucose (16.7 mM) stimulation conditions. For each experiment, IBMX (100 μM) and either 8MM-IBMX (100 μM) (A), cilostamide (1 μM) (B) or rolipram (10 μM) (C) were perfused onto the cell. Pancreatic β-cells were identified using GLP-1 and clonidine as described for Fig 2. Data shown are representative experiments from single human pancreatic β-cells. D) The percent increase in cAMP levels above baseline elicited by PDE inhibitors in human pancreatic β-cells in the presence of 16.7 mM glucose. IBMX, 8MM-IBMX, cilostamide, and rolipram all significantly elevate cAMP levels above baseline and 18G. Furthermore, 8MM-IBMX, cilostamide and rolipram result in significantly less cAMP accumulation compared with IBMX. Last, cilostamide stimulates significantly less cAMP accumulation than rolipram (***, P < 0.001 compared to baseline; ###, P < 0.001, ##, P < 0.01 compared to 18G; †††, P < 0.001 compared to IBMX; ‡, P < 0.05 compared to rolipram; One-way ANOVA with Tukey post-hoc test). Data are shown as mean ± SE from 26 cells (IBMX), 14 cells (8MM-IBMX), 17 cells (cilostamide), and 18 cells (rolipram), collected from four human islet preparations. One outlier was removed for IBMX treatment. E) Comparison of cAMP accumulation stimulated by PDE inhibitors in 1.7 mM (basal) or 16.7 mM glucose. IBMX, 8MM-IBMX, and rolipram stimulated a greater increase in cAMP levels in 16.7 mM glucose, compared to 1.7 mM glucose (***, P < 0.001, **, P < 0.01; Student’s unpaired t-test).