FIGURE 3.

Intracellular glucose levels increased in cells permeabilized with β-escin. A, the initial part of the recording shows a representative recording of the YFP/CFP ratio in a 3T3-L1 adipocyte devoid of response to the exposure to 10 mm extracellular glucose concentration. However, the application of 100 μm β-escin (black box) for 20–30 s caused the nanosensor to respond reversibly to the 10 mm extracellular glucose pulses (rectangular boxes), indicating the normal function of the FLIPglu-600μ sensor. The application of β-escin caused an artifact, which was not displayed (//). B, representative recording of the YFP/CFP ratio in a 3T3-L1 adipocyte that normally responded to the addition of extracellular glucose before the β-escin application. However, after the membrane permeabilization, the delta ratio significantly increased. C, representative recording of the YFP/CFP ratio changes in 3T3-L1 adipocyte unresponsive to 10 mm extracellular glucose concentration. The exposure of cell to iodoacetate (100 μm), an inhibitor of glycolysis, failed to provoke a response to extracellular glucose. Subsequent application of β-escin caused the nanosensor to respond reversibly to the 10 mm extracellular glucose pulse. D, histogram shows delta ratio during changes in extracellular glucose from 0 to 10 mm in fibroblasts (black columns) and in adipocytes (white columns) before and after permeabilization with β-escin. Numbers above columns indicate numbers of cells tested; error bars show S.E. Asterisks indicate significant differences (**, p < 0.01 and ***, p < 0.001, two-way ANOVA).