In the β cell  glucose metabolism turns on two distinct complementary sequences of events known as the triggering pathway and the metabolic amplifying pathway The triggering pathway begins with the raising of the ATP/ADP ratio  which closes KATP channels  depolarizes the cell membrane  activates voltage-gated calcium channels (Ca2+ channels)  and results in calcium influx  which in turn triggers exocytosis of insulin-containing granules (Figure 4)