Salehi Albert, Eliasson Lena, Ma Xiaosong, Rorsman Patrik, Håkanson Rolf, Lundquist Ingmar
Department of Clinical Science, Malmö, Sweden.
Regul Pept. 2007 Mar 1;139(1-3):31-8. doi: 10.1016/j.regpep.2006.10.001. Epub 2006 Nov 15.
Mice were subjected to gastrectomy (GX) or sham operation (controls). Four to six weeks later the pancreatic islets were isolated and analysed for cAMP or alternatively incubated in a Krebs-Ringer based medium in an effort to study insulin secretion and cAMP accumulation in response to glucose or the adenylate cyclase activator forskolin. Freshly isolated islets from GX mice had higher cAMP content than islets from control mice, a difference that persisted after incubation for 1 h at a glucose concentration of 4 mmol/l. Addition of forskolin to this medium induced much greater cAMP and insulin responses in islets from GX mice than in islets from control mice. In contrast, the insulin response to high glucose (16.7 mmol/l) was much weaker in GX islets than in control islets. Glucose-induced insulin release was associated with a 2-fold rise in the cAMP content in control islets. Surprisingly no rise in cAMP was noted in GX islets incubated at high glucose. Capacitance measurements conducted on isolated insulin cells from GX mice revealed a much lower exocytotic response to a single 500 ms depolarisation (from -70 mV to zero) than in control insulin cells. Addition of cAMP to the cytosol enhanced the exocytotic response in insulin cells from control mice but not from GX mice. The depolarisation-triggered inward Ca(2+) current in insulin cells from GX mice did not differ from that in control mice, and hence the reduced exocytotic response following GX cannot be ascribed to a decreased Ca(2+) influx. Experiments involving a train of ten 500 ms depolarisations revealed that the exocytotic response was prominent in control insulin cells but modest in GX insulin cells. It seems that cAMP is capable of eliciting insulin release from insulin cells of GX mice only when cAMP is generated in a specific microdomain conceivably through the intervention of membrane-associated adenylate cyclases that can be activated by forskolin. The GX-evoked impairment of depolarisation-induced exocytosis and glucose-stimulated insulin release may reflect the lack of a gastric agent that serves to maintain an appropriate insulin response to glucose and an appropriate exocytotic response to depolarisation by raising cAMP in a special glucose-sensitive compartment possibly regulated by a soluble adenylate cyclase.
将小鼠进行胃切除术（GX）或假手术（作为对照）。4至6周后，分离胰腺胰岛并分析其环磷酸腺苷（cAMP）含量，或者将胰岛置于基于 Krebs-Ringer 的培养基中孵育，以研究胰岛素分泌以及对葡萄糖或腺苷酸环化酶激活剂福斯高林的反应中 cAMP 的积累情况。来自 GX 小鼠的新鲜分离胰岛的 cAMP 含量高于对照小鼠的胰岛，在 4 mmol/l 的葡萄糖浓度下孵育 1 小时后，这种差异仍然存在。向该培养基中添加福斯高林后，GX 小鼠胰岛中诱导产生的 cAMP 和胰岛素反应比对照小鼠胰岛中的大得多。相比之下，GX 胰岛对高葡萄糖（16.7 mmol/l）的胰岛素反应比对照胰岛弱得多。葡萄糖诱导的胰岛素释放与对照胰岛中 cAMP 含量升高两倍相关。令人惊讶的是，在高葡萄糖条件下孵育的 GX 胰岛中未观察到 cAMP 升高。对来自 GX 小鼠的分离胰岛素细胞进行的电容测量显示，与对照胰岛素细胞相比，对单次 500 毫秒去极化（从 -70 mV 到零）的胞吐反应要低得多。向细胞质中添加 cAMP 增强了对照小鼠胰岛素细胞的胞吐反应，但未增强 GX 小鼠胰岛素细胞的胞吐反应。GX 小鼠胰岛素细胞中去极化触发的内向 Ca(2+)电流与对照小鼠的无差异。因此，GX 后胞吐反应降低不能归因于 Ca(2+)内流减少。涉及十次 500 毫秒去极化序列的实验表明，对照胰岛素细胞中的胞吐反应明显，而 GX 胰岛素细胞中的胞吐反应适度。似乎只有当 cAMP 在特定微区产生时，cAMP 才能够从 GX 小鼠的胰岛素细胞中引发胰岛素释放，这种特定微区可能是通过可被福斯高林激活的膜相关腺苷酸环化酶的干预而形成的。GX 引起的去极化诱导的胞吐作用和葡萄糖刺激的胰岛素释放受损可能反映出缺乏一种胃因子，该因子通过在可能由可溶性腺苷酸环化酶调节的特殊葡萄糖敏感区室中提高 cAMP 来维持对葡萄糖的适当胰岛素反应和对去极化的适当胞吐反应。
