Rorsman P, Trube G
J Physiol. 1986 May;374:531-50. doi: 10.1113/jphysiol.1986.sp016096.
Pancreatic islets of NMRI mice were dissociated into single cells which were kept in tissue culture for 1-3 days. The whole-cell configuration of the patch-clamp technique was used to study inward and delayed outward currents of beta-cells under voltage-clamp conditions at 20-22 degrees C. Outward currents were suppressed by substituting the impermeant cation N-methyl-D-glucamine for intracellular K+. The remaining inward current had a V-shaped current-voltage relation reaching a peak value of 39 +/- 4 pA (mean +/- S.E. of mean) around -15 mV. It was identified as a Ca2+ current, because the peak amplitude was increased 1.6 times by increasing external [Ca2+] ([Ca2+]o) from 2.6 mM to 10 mM and it was blocked by Co2+ (5 mM) or nifedipine (5 microM) but not by TTX (20 microM). The activation time constant of the inward current at -10 mV was 1.28 +/- 0.08 ms. The relation between the degree of activation (estimated from the size of the tail currents) and membrane potential V followed the sigmoidal function f = 1/(1 + exp [(Vh-V)/k]) with half-maximal activation potential, Vh = 4 +/- 1 mV and slope factor, k = 14 +/- 1 mV (for [Ca2+]o 10 mM). The inward current inactivated only weakly during depolarizing pulses of 0.1-1 s duration. The delayed outward current (in experiments with 155 mM-internal [K+] ([K+]i)) had a linear voltage dependence at potentials above -20 mV; its amplitude at -10 mV was 210 +/- 30 pA. Tail currents related to the activation of the outward current had K+-dependent reversal potentials. The current was blocked by extracellularly applied tetraethylammonium (20 mM) and 4-aminopyridine (2 mM). It was not affected by glibenclamide (3 microM), tolbutamide (0.2 mM) and alterations of intracellular [Ca2+] (1 nM-1 microM). The activation time constant of the outward current at -10 mV was 21 +/- 3 ms. The voltage dependence of activation could be described by the sigmoidal function (see above) with Vh = 19 +/- 1 mV and k = 5.6 +/- 0.4 mV. The outward current inactivated during long (15 s) depolarizing pre-pulses (time constant at -10 mV: 2.6 +/- 0.6 s). 50% inactivation occurred at Vh = -36 +/- 2 mV, k was -4.1 +/- 0.2 mV. Inward and outward currents during depolarizing voltage pulses in beta-cells are similar to Ca2+ and delayed K+ currents in other cell types. These currents seem sufficient to generate the action potentials of the beta-cell.
将NMRI小鼠的胰岛解离成单细胞，并在组织培养中保存1 - 3天。采用膜片钳技术的全细胞配置，在20 - 22℃的电压钳条件下研究β细胞的内向电流和延迟外向电流。通过用不透性阳离子N - 甲基 - D - 葡糖胺替代细胞内K⁺来抑制外向电流。剩余的内向电流具有V形电流 - 电压关系，在约 - 15 mV时达到峰值39±4 pA（平均值±平均值的标准误）。它被鉴定为Ca²⁺电流，因为通过将细胞外[Ca²⁺]（[Ca²⁺]o）从2.6 mM增加到10 mM，峰值幅度增加了1.6倍，并且它被Co²⁺（5 mM）或硝苯地平（5 μM）阻断，但不被TTX（20 μM）阻断。在 - 10 mV时内向电流的激活时间常数为1.28±0.08 ms。激活程度（根据尾电流大小估计）与膜电位V之间的关系遵循S形函数f = 1/(1 + exp[(Vh - V)/k])，其中半最大激活电位Vh = 4±1 mV，斜率因子k = 14±1 mV（对于[Ca²⁺]o 10 mM）。在0.1 - 1 s持续时间的去极化脉冲期间，内向电流仅微弱失活。延迟外向电流（在细胞内[K⁺]（[K⁺]i）为155 mM的实验中）在电位高于 - 20 mV时具有线性电压依赖性；其在 - 10 mV时的幅度为210±30 pA。与外向电流激活相关的尾电流具有K⁺依赖性反转电位。该电流被细胞外施加的四乙铵（20 mM）和4 - 氨基吡啶（2 mM）阻断。它不受格列本脲（3 μM）、甲苯磺丁脲（0.2 mM）和细胞内[Ca²⁺]变化（1 nM - 1 μM）的影响。在 - 10 mV时外向电流的激活时间常数为21±3 ms。激活的电压依赖性可以用S形函数（见上文）描述，其中Vh = 19±1 mV，k = 5.6±0.4 mV。外向电流在长时间（15 s）去极化预脉冲期间失活（在 - 10 mV时的时间常数：2.6±0.6 s）。50%失活发生在Vh = - 36±2 mV时，k为 - 4.1±0.2 mV。β细胞去极化电压脉冲期间的内向电流和外向电流类似于其他细胞类型中的Ca²⁺电流和延迟K⁺电流。这些电流似乎足以产生β细胞的动作电位。
