Westerlund J, Ortsäter H, Palm F, Sundsten T, Bergsten P
Department of Medical Cell Biology, Biomedical Center, Uppsala University, Box 571, SE-751 23 Uppsala, Sweden.
Eur J Endocrinol. 2001 Jun;144(6):667-75. doi: 10.1530/eje.0.1440667.
Regulation of insulin release by glucose involves dual pathways, including or not inhibition of ATP-sensitive K(+) channels (K(ATP) channels). Whereas the K(ATP) channel-dependent pathway produces pulsatile release of insulin it is not clear whether the independent pathway also generates such kinetics.
To clarify this matter, insulin secretion and cytoplasmic Ca(2+) (Ca(2+)) were studied in perifused pancreatic islets from ob/ob mice. Insulin release was measured by ELISA technique and Ca(2+) by dual-wavelength fluorometry.
Insulin secretion was pulsatile (0.2--0.3/min) at 3 mmol/l glucose when Ca(2+) was low and stable. Stimulation with 11 mmol/l of the sugar increased the amplitude of the insulin pulses with maintained frequency and induced oscillations in Ca(2+). Permanent opening of the K(ATP) channels with diazoxide inhibited glucose-stimulated insulin secretion back to basal levels with maintained pulsatility despite stable and basal Ca(2+) levels. Increase of the K(+) concentration to 30.9 mmol/l in the continued presence of diazoxide and 11 mmol/l glucose restored the secretory rate with maintained pulsatility and caused stable elevation in Ca(2+). Simultaneous introduction of diazoxide and elevation of K(+) augmented average insulin release almost 30-fold in 3 mmol/l glucose with maintained pulse frequency. Subsequent elevation of the glucose concentration to 11 and 20 mmol/l increased the release levels. After prolonged exposure to diazoxide, elevated K(+) and 20 mmol/l glucose, the pulse frequency decreased significantly.
Not only glucose signaling via the K(ATP) channel-dependent but also that via the independent pathway generates amplitude-modulated pulsatile release of insulin from isolated islets.
葡萄糖对胰岛素释放的调节涉及两条途径，包括或不包括对ATP敏感性钾通道（KATP通道）的抑制。虽然依赖KATP通道的途径产生胰岛素的脉冲式释放，但尚不清楚独立途径是否也产生这种动力学。
为阐明这一问题，对ob/ob小鼠的胰腺胰岛进行灌流研究胰岛素分泌和细胞质钙（[Ca2+]i）。通过ELISA技术测量胰岛素释放，通过双波长荧光法测量[Ca2+]i。
当[Ca2+]i较低且稳定时，在3 mmol/l葡萄糖浓度下胰岛素分泌呈脉冲式（0.2 - 0.3次/分钟）。用11 mmol/l的糖刺激增加了胰岛素脉冲的幅度，频率保持不变，并诱导了[Ca2+]i的振荡。用二氮嗪使KATP通道永久开放，抑制葡萄糖刺激的胰岛素分泌回到基础水平，尽管[Ca2+]i水平稳定且处于基础状态，但仍保持脉冲性。在持续存在二氮嗪和11 mmol/l葡萄糖的情况下，将钾浓度增加到30.9 mmol/l可恢复分泌率，保持脉冲性，并导致[Ca2+]i稳定升高。同时引入二氮嗪和提高钾浓度可使3 mmol/l葡萄糖中的平均胰岛素释放增加近30倍，脉冲频率保持不变。随后将葡萄糖浓度提高到11和20 mmol/l可增加释放水平。在长时间暴露于二氮嗪、高钾和20 mmol/l葡萄糖后，脉冲频率显著降低。
不仅通过依赖KATP通道的葡萄糖信号传导，而且通过独立途径的信号传导都能从分离的胰岛产生幅度调制的胰岛素脉冲式释放。
