Nilsson T, Arkhammar P, Hallberg A, Hellman B, Berggren P O
Department of Medical Cell Biology, Biomedicum, Uppsala, Sweden.
Biochem J. 1987 Dec 1;248(2):329-36. doi: 10.1042/bj2480329.
Pancreatic beta-cells isolated from obese-hyperglycaemic mice released intracellular Ca2+ in response to carbamoylcholine, an effect dependent on the presence of glucose. The effective Ca2+ concentration reached was sufficient to evoke a transient release of insulin. When the cells were deficient in Ca2+, the Ca2+ pool sensitive to carbamoylcholine stimulation was equivalent to that released by ionomycin. Unlike intact cells, cells permeabilized by high-voltage discharges failed to generate either inositol 1,4,5-triphosphate (InsP3) or to release Ca2+ after exposure to carbamoylcholine. However, the permeabilized cells released insulin sigmoidally in response to increasing concentrations of Ca2+. Also in the absence of functional mitochondria these cells exhibited a large ATP-dependent buffering of Ca2+, enabling the maintenance of an ambient Ca2+ concentration corresponding to about 150 nM even after several additional pulses of Ca2+. InsP3, maximally effective at 6 microM, promoted a rapid and pronounced release of Ca2+. The InsP3-sensitive Ca2+ pool was rapidly filled and lost its Ca2+ late after ATP depletion. The transient nature of the Ca2+ signal was not overcome by repetitive additions of InsP3. It was possible to restore the response to InsP3 after a delay of approx. 20 min, an effect which had less latency after the addition of Ca2+. These latter findings argue against degradation and/or desensitization as factors responsible for the transiency in InsP3 response. It is suggested that Ca2+ released by InsP3 is taken up by a part of the endoplasmic reticulum (ER) not sensitive to InsP3. On metabolism of InsP3, Ca2+ recycles to the InsP3-sensitive pool, implying that this pool indeed has a very high affinity for the ion. The presence of functional mitochondria did not interfere with the recycling process. The ER in pancreatic beta-cells is of major importance in buffering Ca2+, but InsP3 only modulates Ca2+ transport for a restricted period of time following immediately upon its formation. Thereafter the non-sensitive part of the ER takes over the continuous regulation of Ca2+ cycling.
从肥胖高血糖小鼠分离出的胰腺β细胞，在对氨甲酰胆碱产生反应时会释放细胞内Ca2+，这一效应依赖于葡萄糖的存在。所达到的有效Ca2+浓度足以引发胰岛素的瞬时释放。当细胞缺乏Ca2+时，对氨甲酰胆碱刺激敏感的Ca2+池与离子霉素释放的Ca2+池相当。与完整细胞不同，经高压放电通透化处理的细胞在暴露于氨甲酰胆碱后既不产生肌醇1,4,5-三磷酸（InsP3）也不释放Ca2+。然而，通透化细胞在Ca2+浓度增加时呈S形释放胰岛素。同样在缺乏功能性线粒体的情况下，这些细胞表现出对Ca2+的大量ATP依赖性缓冲作用，即使在额外多次施加Ca2+脉冲后，仍能维持约150 nM的细胞外Ca2+浓度。InsP3在6 microM时效果最佳，能促进Ca2+的快速且显著释放。InsP3敏感的Ca2+池迅速被填满，并在ATP耗尽后很久才失去其Ca2+。Ca2+信号的瞬态性质不会因重复添加InsP3而被克服。在大约延迟20分钟后有可能恢复对InsP3的反应，添加Ca2+后这种效应的延迟时间更短。这些后期发现反对将降解和/或脱敏作为InsP3反应瞬态性的原因。有人提出，InsP3释放的Ca2+被内质网（ER）中对InsP3不敏感的部分摄取。在InsP3代谢后，Ca2+循环回到InsP3敏感池，这意味着该池对该离子确实具有非常高的亲和力。功能性线粒体的存在并不干扰循环过程。胰腺β细胞中的内质网在缓冲Ca2+方面至关重要，但InsP3仅在其形成后立即的一段有限时间内调节Ca2+转运。此后，内质网的不敏感部分接管Ca2+循环的持续调节。
