measured using a rat RIA kit (Cat number: EZRMI-13K, Millipore, Germany). First, the cells of each group
were exposed to glucose-free Krebs-Ringer Bicarbonate
(KRB). Then, the cells were divided into three groups and
exposed to KRB containing different concentrations of
glucose 5.56, 16.7 and 25 mmol/L for one hour. Then, the
media were removed and kept in a -80°C freezer till use.
Finally, insulin secretion was measured by the rat RIA kit
(Cat number: EZRMI-13K, Millipore, Germany).