Ahrén B, Lundquist I
Pharmacology. 1985;30(2):71-82. doi: 10.1159/000138053.
It has previously been demonstrated in several species that the secretory granules of pancreatic beta-cells have the ability to store substantial amounts of calcium and bioactive amines, such as dopamine and serotonin. Furthermore, evidence for a similar topographical localization for amine and calcium within the periphery of the granules has been obtained. In the present study, a possible interaction between dopamine and calcium on insulin release was investigated. Isolated rat islets were loaded with 45Ca2+ in the presence of theophylline and high glucose and then perifused in a dynamic system where radioactivity and insulin were determined in the effluent. When perifused in a bicarbonate buffer with 2 mmol/l Ca2+ and supplemented with the monoamine oxidase inhibitor pargyline, L-3,4-dihydroxyphenylalanine (L-dopa)-induced dopamine accumulation in the islets brought about a slight and transient increase in 45Ca2+ efflux. This increase was more pronounced and sustained in a Ca2+-deficient buffer or in a Ca2+-deficient buffer supplemented with ethyleneglycolbis(aminoethylether)tetraacetic acid (EGTA). Insulin release was transiently stimulated by islet dopamine accumulation in the Ca2+-deprived media, but not in a medium with 2 mmol/l Ca2+. Glucose-induced insulin release in 2 mmol/l Ca2+ was potentiated by acute dopamine accumulation. The combined effect of glucose stimulation and islet accumulation of dopamine induced a transient insulin release in the Ca2+-deprived media with and without EGTA. This release of insulin was accompanied by an increased 45Ca2+ efflux which was most pronounced in the presence of EGTA. Stimulation with glucose alone, i.e. without addition of L-dopa tended to decrease insulin release and 45Ca2+ efflux in a Ca2+-deficient medium. No effects of L-dopa or L-dopa + glucose were encountered in a Ca2+-deficient buffer when the monoamine oxidase inhibitor pargyline was replaced by the dopa-decarboxylase inhibitor benserazide. The results are interpreted as being a consequence of a complex interaction between the accumulated dopamine and a pool of Ca2+ mainly confined to the secretory granules. This interaction could be followed by a transient increase in cytosolic Ca2+ and a subsequent efflux of Ca2+ out of the cell, eventually accompanied by insulin release. Increasing the cytosolic Ca2+ by acute dopamine accumulation makes the cell more sensitive to a concomitant stimulation with glucose, and the release of insulin is triggered. A long-term dopamine accumulation. On the other hand, might diminish the granular Ca2+ pool to such a level where insulin release is inhibited after stimulation with certain secretagogues.
此前在多个物种中已证实，胰腺β细胞的分泌颗粒有能力储存大量钙和生物活性胺，如多巴胺和5-羟色胺。此外，已获得证据表明颗粒外周的胺和钙有类似的拓扑定位。在本研究中，对多巴胺和钙在胰岛素释放上的可能相互作用进行了研究。将分离的大鼠胰岛在茶碱和高糖存在的情况下用45Ca2+加载，然后在动态系统中进行灌流，在流出物中测定放射性和胰岛素。当在含2 mmol/l Ca2+的碳酸氢盐缓冲液中灌流并补充单胺氧化酶抑制剂优降宁时，L-3,4-二羟基苯丙氨酸（L-多巴）诱导的胰岛多巴胺积累使45Ca2+外流有轻微且短暂的增加。在缺钙缓冲液或补充了乙二醇双（氨基乙基醚）四乙酸（EGTA）的缺钙缓冲液中，这种增加更明显且持续。在缺钙培养基中，胰岛多巴胺积累可短暂刺激胰岛素释放，但在含2 mmol/l Ca2+的培养基中则不然。急性多巴胺积累可增强2 mmol/l Ca2+时葡萄糖诱导的胰岛素释放。葡萄糖刺激和胰岛多巴胺积累的联合作用在含和不含EGTA的缺钙培养基中均诱导短暂的胰岛素释放。这种胰岛素释放伴随着45Ca2+外流增加，在有EGTA存在时最为明显。单独用葡萄糖刺激，即在不添加L-多巴的情况下，往往会降低缺钙培养基中的胰岛素释放和45Ca2+外流。当用多巴脱羧酶抑制剂苄丝肼取代单胺氧化酶抑制剂优降宁时，在缺钙缓冲液中未观察到L-多巴或L-多巴 + 葡萄糖的作用。结果被解释为积累的多巴胺与主要局限于分泌颗粒的钙池之间复杂相互作用的结果。这种相互作用之后可能是胞质钙短暂增加，随后钙外流到细胞外，最终伴随着胰岛素释放。通过急性多巴胺积累增加胞质钙会使细胞对同时的葡萄糖刺激更敏感，并触发胰岛素释放。另一方面，长期的多巴胺积累可能会使颗粒钙池减少到这样一个水平，即在用某些促分泌剂刺激后胰岛素释放受到抑制。
