Sherman A, Xu L, Stokes C L
National Institutes of Health, Bethesda, Maryland 20892.
J Membr Biol. 1995 Jan;143(1):79-87. doi: 10.1007/BF00232525.
The quantitative characterization of ion channel properties in pancreatic beta-cells under typical patch clamp conditions can be questioned because of the unreconciled differences in experimental conditions and observed behavior between microelectrode recordings of membrane potential in intact islets of Langerhans and patch recordings of single cells. Complex bursting is reliably observed in islets but not in isolated cells under patch clamp conditions. E. Rojas et al. (J. Membrane Biol. 143:65-77, 1995) have attempted to circumvent these incompatibilities by measuring currents in beta-cells in intact islets by voltage-clamping with intracellular microelectrodes (150-250 M omega tip resistance). The major potential pitfall is that beta-cells within the islet are electrically coupled, and contaminating coupling currents must be subtracted from current measurements, just as linear leak currents are typically subtracted. To characterize the conditions under which such coupling current subtraction is valid, we have conducted a computational study of a model islet. Assuming that the impaled cell is well clamped, we calculate the native and coupling components of the observed current. Our simulations illustrate that coupling can be reliably subtracted when neighbor cells' potentials are constant or vary only slowly (e.g., during their silent phases) but not when they vary rapidly (e.g., during their active phases). We also show how to estimate coupling conductances in the intact islet from measurements of coupling currents.
在典型的膜片钳条件下，胰岛β细胞离子通道特性的定量表征可能受到质疑，因为在完整胰岛中膜电位的微电极记录与单细胞的膜片钳记录之间，实验条件和观察到的行为存在无法协调的差异。在胰岛中能可靠地观察到复杂的爆发式活动，但在膜片钳条件下的分离细胞中却观察不到。E. 罗哈斯等人（《膜生物学杂志》143:65 - 77, 1995）试图通过用细胞内微电极（尖端电阻为150 - 250 MΩ）进行电压钳制来测量完整胰岛中β细胞的电流，以规避这些不兼容性。主要的潜在问题在于，胰岛内的β细胞是电耦合的，就像通常减去线性漏电流一样，必须从电流测量值中减去污染性的耦合电流。为了表征这种耦合电流减法有效的条件，我们对一个胰岛模型进行了计算研究。假设刺入的细胞被良好钳制，我们计算观察到的电流的固有成分和耦合成分。我们的模拟表明，当相邻细胞的电位恒定或变化缓慢（例如，在它们的静息期）时，可以可靠地减去耦合电流，但当它们快速变化（例如，在它们的活动期）时则不行。我们还展示了如何根据耦合电流的测量值来估计完整胰岛中的耦合电导。
