Figure 5.

Stimulation of insulin secretion by glucose in INS-r3-GK27 cells with various levels of glucokinase. Cells were cultured with doxycycline in the presence of 2.5 mM glucose for 14 h. They then were incubated in Krebs–Ringer medium with the specified glucose concentrations for 30 min. Insulin released in the medium was assayed by radioimmunoassay and expressed per μg of cellular DNA content. Data were calculated as ratios of amounts of insulin release over the amount of insulin released by cells cultured without doxycycline at 2.5 mM glucose. This reference value amounted to 0.054 ± 0.010 ng of insulin/μg of DNA. Data represent the means ± SEM of six separate experiments. In each experiment, measurements were performed in duplicates for each experimental condition. Cellular insulin content of cells cultured without doxycycline was 46 ± 6 ng/μg of DNA. Cellular insulin content was decreased 20% in cells cultured with 500 ng/ml doxycycline.