Figure 4.

Measurement of functional β-cell mass. A) Schematic illustration of βFLUOMETRI. Although all cells express Cerulean under the CMV promoter, all endocrine cells express EGFP under the rat β-cell-active glucokinase promoter fragment bGK-278, and only β cells express DsRed2 under the insulin promoter fragment RIP1-410. Cerulean under the CMV promoter was used for normalization of fluorescence changes in EGFP under bGK-278 and DsRed2 under RIP1-410. B) Schematic illustration of the metabolic response elements within RIP1-410 and bGK-278. Elements highlighted in green are glucose and insulin responsive; that in yellow is glucose responsive, and NFAT and CRE are Ca²⁺ responsive. C) Representative image of an islet expressing βFLUOMETRI (n = 6). Scale bars, 50 µm. D) Changes in EGFP, DsRed2, and Cerulean (CFP) fluorescence after glucose stimulation in islets in vitro (n = 6). E) Promoter activation after glucose stimulation in vitro. DsRed2 and EGFP fluorescence intensities were normalized to CFP fluorescence intensity (n = 6). F) Activation of RIP1-410 and bGK-278 after glucose and saline injection in vivo (n = 5). ***P < 0.001. Data are expressed as means ± sem. See also Supplemental Fig. S3.