Wang L, Bhattacharjee A, Fu J, Li M
Department of Pharmacology, University of South Alabama, College of Medicine, Mobile 36688, USA.
Diabetes. 1996 Dec;45(12):1678-83. doi: 10.2337/diab.45.12.1678.
A macroscopic low-voltage-activated (LVA) inward current was found in pancreatic beta-cells isolated from NOD mice. However, this current was not present in nondiabetic prone mouse (e.g., Swiss-Webster) pancreatic beta-cells. We performed pharmacological analyses on this current in NOD insulinoma tumor cells (NIT-1). This cell line was developed from pancreatic beta-cells of a transgenic NOD mouse. The sodium-channel blocker, tetrodotoxin (TTX; 2 micromol/l) had no effect on this LVA current. The amplitudes of currents elicited by a -20 mV test pulse retained similarity when the extracellular sodium concentration was increased from 0 to 115 mmol/l; when the extracellular calcium concentration was decreased from 10 to 2 mmol/l, there was an approximate 50% reduction of this current elicited by a -30 mV test pulse. Neither the L-type calcium-channel blocker, nifedipine (3 micromol/l), nor the N-type calcium-channel blocker, omega-CgTx-GVIA (1 micromol/l), at -30 mV produced an appreciable effect. The T-type calcium-channel blockers, nickel (3 micromol/l) and amiloride (250 micromol/l), effectively reduced the peak of this current. In 2 mmol/l calcium external solution, the threshold of voltage-dependent activation of this calcium current was approximately -65 mV, and the peak current occurred at -20 mV. Half-maximum steady-state inactivation was around -43 mV. The mean time constant of slow deactivating tail currents generated by a preceding 20 mV pulse was 2.53 ms. The intracellular free calcium concentration was two- to threefold higher in NOD mouse pancreatic beta-cells compared with Swiss-Webster pancreatic beta-cells. We concluded that there are LVA calcium channels abnormally expressed in NOD mouse beta-cells. This LVA calcium channel may be factorial to the high cytosolic free calcium concentration observed in these cells, and thereby may contribute to the pathogenesis of NOD mouse beta-cells.
在从非肥胖型糖尿病（NOD）小鼠分离出的胰腺β细胞中发现了一种宏观的低电压激活（LVA）内向电流。然而，这种电流在非糖尿病倾向小鼠（如瑞士 Webster 小鼠）的胰腺β细胞中并不存在。我们对 NOD 胰岛素瘤肿瘤细胞（NIT-1）中的这种电流进行了药理学分析。该细胞系由转基因 NOD 小鼠的胰腺β细胞发育而来。钠通道阻滞剂河豚毒素（TTX；2 μmol/L）对这种 LVA 电流没有影响。当细胞外钠浓度从 0 增加到 115 mmol/L 时，由 -20 mV 测试脉冲引发的电流幅度保持相似；当细胞外钙浓度从 10 降低到 2 mmol/L 时，由 -30 mV 测试脉冲引发的这种电流大约降低了 50%。在 -30 mV 时，L 型钙通道阻滞剂硝苯地平（3 μmol/L）和 N 型钙通道阻滞剂ω-芋螺毒素 GVIA（1 μmol/L）均未产生明显作用。T 型钙通道阻滞剂镍（3 μmol/L）和阿米洛利（250 μmol/L）有效降低了这种电流的峰值。在 2 mmol/L 钙的外部溶液中，这种钙电流的电压依赖性激活阈值约为 -65 mV，峰值电流出现在 -20 mV 处。半数最大稳态失活约为 -43 mV。由之前的 20 mV 脉冲产生的缓慢失活尾电流的平均时间常数为 2.53 ms。与瑞士 Webster 小鼠的胰腺β细胞相比，NOD 小鼠胰腺β细胞中的细胞内游离钙浓度高两到三倍。我们得出结论，NOD 小鼠β细胞中存在异常表达的 LVA 钙通道。这种 LVA 钙通道可能是导致这些细胞中观察到的高细胞质游离钙浓度的因素，从而可能促成 NOD 小鼠β细胞的发病机制。
