Pian-Smith M C, Yada T, Yaney G C, Abdel el Motal S M, Wiedenkeller D E, Sharp G W
Department of Pharmacology, New York State College of Veterinary Medicine, Cornell University, Ithaca 14853.
Endocrinology. 1988 Oct;123(4):1984-91. doi: 10.1210/endo-123-4-1984.
TMB-8 has been used experimentally in many cell types, including endocrine cells, because of its ability to block the efflux of Ca2+ from intracellular stores without affecting influx. Unexpectedly, TMB-8 potentiates stimulated insulin release from pancreatic islets, a process believed to be dependent on the level of cytosolic Ca2+. In the present study, while having no effect on basal insulin release (in the presence of 2.8 mM glucose), TMB-8 (10, 30, and 100 microM) caused a concentration-dependent increase in 45Ca2+ efflux from 45Ca2+-preloaded islets. TMB-8 (100 microM) stimulated 45Ca2+ efflux even in the absence of extracellular Ca2+. In the presence of 5.6 mM glucose, TMB-8 (30 and 100 microM) potentiated insulin release and again increased 45Ca2+ efflux in a concentration-dependent manner. Similarly, insulin release stimulated by isobutylmethylxanthine (IBMX) was potentiated significantly, and IBMX-stimulated 45Ca2+ efflux was increased by the simultaneous introduction of 30 microM TMB-8. Thus, in pancreatic islets, TMB-8 appears to mobilize Ca2+ from intracellular stores, rather than inhibit the efflux as has been commonly accepted. In further studies, using insulin-secreting beta-cells of the RINm5F cell line, TMB-8 was shown to increase the cytosolic Ca2+ concentration in the presence and absence of extracellular Ca2+. This confirmed that mobilization of intracellular Ca2+ was occurring in the pancreatic beta-cell in response to TMB-8. Furthermore, a rise in cytosolic Ca2+ of not more than 10 nM (as induced with KCl) was found to mimick the effect of TMB-8 in conjunction with IBMX. No additional effect of TMB-8 to alter Ca2+ handling at the plasma membrane was found when 45Ca2+ uptake experiments were performed. Therefore, the paradoxical mobilization of beta-cell Ca2+ by TMB-8 appears to be a sufficient explanation for its potentiating effect on the rate of insulin secretion.
由于TMB - 8能够阻断Ca2 +从细胞内储存库的外流而不影响其流入，因此已在包括内分泌细胞在内的多种细胞类型中进行了实验应用。出乎意料的是，TMB - 8增强了胰腺胰岛刺激后的胰岛素释放，这一过程被认为依赖于胞质Ca2 +的水平。在本研究中，虽然TMB - 8（10、30和100微摩尔）对基础胰岛素释放（在2.8毫摩尔葡萄糖存在下）没有影响，但却导致45Ca2 +从预先加载45Ca2 +的胰岛中流出呈浓度依赖性增加。即使在没有细胞外Ca2 +的情况下，TMB - 8（100微摩尔）也能刺激45Ca2 +外流。在5.6毫摩尔葡萄糖存在下，TMB - 8（30和100微摩尔）增强了胰岛素释放，并再次以浓度依赖性方式增加了45Ca2 +外流。同样，异丁基甲基黄嘌呤（IBMX）刺激的胰岛素释放也显著增强，同时引入30微摩尔TMB - 8可增加IBMX刺激的45Ca2 +外流。因此，在胰腺胰岛中，TMB - 8似乎是从细胞内储存库中动员Ca2 +，而不是像通常所认为的那样抑制外流。在进一步的研究中，使用RINm5F细胞系分泌胰岛素的β细胞，结果显示在有或没有细胞外Ca2 +的情况下，TMB - 8都会增加胞质Ca2 +浓度。这证实了胰腺β细胞中响应TMB - 8发生了细胞内Ca2 +的动员。此外，发现胞质Ca2 +升高不超过10纳摩尔（如用氯化钾诱导）与TMB - 8联合IBMX具有相似的作用。当进行45Ca2 +摄取实验时，未发现TMB - 8对改变质膜上Ca2 +处理有额外影响。因此，TMB - 8对β细胞Ca2 +的反常动员似乎足以解释其对胰岛素分泌速率的增强作用。
