After uptake of glucose pancreatic beta-cell glucose is rapidly degraded in oxidative glucose metabolism, leading to ATP formation. ATP is involved in beta-cell membrane depolarization. The ADP/ATP ratio, the sulfonylurea receptor-1 (SUR 1) protein, which closes the adjacent potassium channel (potassium inward rectifier 6.2, KIR 6.2 channel). The closure of the potassium channels will decrease the membrane potential, which leads to opening of voltage-gated calcium channels; this induces the release of insulin-containing granules (Fig. 5). Upon stimulation with glucose, insulin is released with a short-lasting peak of a few minutes (so-called "first-phase") followed by a slowly evolving second phase; the second phase lasts as long as the plasma glucose level is elevated.
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