Plasman P O, Herchuelz A
Laboratoire de Pharmacodynamie et de Thérapeutique, Université Libre de Bruxelles, Faculté de Médecine, Belgium.
Biochem J. 1992 Jul 1;285 ( Pt 1)(Pt 1):123-7. doi: 10.1042/bj2850123.
Na+/Ca2+ exchange in the B cell was recently characterized by measuring intracellular-Na(+)-dependent 45Ca2+ uptake in isolated rat pancreatic islet cells. The aim of the present study was to investigate the regulation of this process. Extracellular pH (pHo) and intracellular pH (pHi) markedly affected Na+/Ca2+ exchange. A fall of 0.04 unit in pHi decreased the exchange by 45%, whereas a rise of 0.13 unit increased the uptake by 70%. Mitochondrial poisons (oligomycin, antimycin A and 2,4-dinitrophenol) inhibited reverse Na+/Ca2+ exchange by about 25-50%. The exchanger displayed a low Q10 (temperature coefficient), indicating that it is only indirectly dependent on metabolic energy. The phorbol ester phorbol 12-myristate 13-acetate did not affect Na+/Ca2+ exchange. Likewise, lowering the extracellular K+ concentration did not inhibit 45Ca2+ uptake. In conclusion, the pHi and the metabolic state of the cell may represent important modulatory signals by which insulin secretagogues such as glucose could regulate reverse Na+/Ca2+ exchange in the B cell. The process does not appear to co-transport K+ nor to be influenced by protein kinase C.
最近通过测量分离的大鼠胰岛细胞中细胞内钠依赖性45Ca2+摄取来表征B细胞中的钠钙交换。本研究的目的是研究该过程的调节机制。细胞外pH（pHo）和细胞内pH（pHi）对钠钙交换有显著影响。pHi下降0.04个单位会使交换减少45%，而pHi上升0.13个单位会使摄取增加70%。线粒体毒物（寡霉素、抗霉素A和2,4-二硝基苯酚）可抑制反向钠钙交换约25%-50%。该交换体显示出较低的Q10（温度系数），表明它仅间接依赖于代谢能量。佛波酯佛波醇12-肉豆蔻酸酯13-乙酸酯不影响钠钙交换。同样，降低细胞外钾离子浓度也不抑制45Ca2+摄取。总之，pHi和细胞的代谢状态可能是重要的调节信号，通过这些信号，诸如葡萄糖等胰岛素促分泌剂可调节B细胞中的反向钠钙交换。该过程似乎不协同转运钾离子，也不受蛋白激酶C的影响。
