FIGURE 3.

GLP-1 stimulates activation of a FRET-based GCK reporter in living cells. A, βTC3 cells expressing the WT FRET-GCK reporter were stimulated with 30 nm GLP-1 (5 min). The normalized FRET ratio was calculated before (black) and after (white) stimulation for individual cells. Statistical significance from pretreatment FRET ratio (p < 0.01, n = 7 cells, two-tailed t test) is denoted by **. B, cells expressing the WT FRET-GCK reporter were pretreated with the NOS inhibitor l-NAME (5 mm, 10 min) prior to stimulation with GLP-1 (30 nm, 5 min). The same cells were subsequently treated with a NO donor (100 μm, SNAP, 1 min). (***, p < 0.001 versus l-NAME and prestimulation, ANOVA, Tukey multiple comparison, n = 7 cells). C, cells expressing a FRET-GCK sensor containing the V367M mutation were treated as in A. The poststimulation FRET ratio was not significantly different from the prestimulation FRET ratio (p > 0.05, two-tailed t test, n = 8 cells). Bars indicate mean ± S.E. (error bars) for all groups.