Silver M R, DeCoursey T E
Department of Medicine, Rush Medical Center, Chicago, Illinois 60612.
J Gen Physiol. 1990 Jul;96(1):109-33. doi: 10.1085/jgp.96.1.109.
Inward rectifier (IR) currents were studied in bovine pulmonary artery endothelial cells in the whole-cell configuration of the patch-clamp technique with extracellular K+ concentrations, [K+]o, ranging from 4.5 to 160 mM. Whether the concentration of free Mg2+ in the intracellular solution, [Mg2+]i, was 1.9 mM or nominally 0, the IR exhibited voltage- and time-dependent gating. The IR conductance was activated by hyperpolarization and deactivated by depolarization. Small steady-state outward IR currents were present up to approximately 40 mV more positive than the K+ reversal potential, EK, regardless of [Mg2+]i. Modeled as a first-order C in equilibrium O gating process, both the opening rate, alpha, and the closing rate, beta, were exponentially dependent on voltage, with beta more steeply voltage dependent, changing e-fold for 9 mV compared with 18 mV for an e-fold change in alpha. Over all [K+]o studied, the voltage dependence of alpha and beta shifted along with EK, as is characteristic of IR channels in other cells. The steady-state voltage dependence of the gating process was well described by a Boltzmann function. The half-activation potential was on average approximately 7 mV negative to the observed reversal potential in all [K+]o regardless of [Mg2+]i. The activation curve was somewhat steeper when Mg-free pipette solutions were used (slope factor, 4.3 mV) than when pipettes contained 1.9 mM Mg2+ (5.2 mV). The simplest interpretation of these data is that IR channels in bovine pulmonary artery endothelial cells have an intrinsic gating mechanism that is not due to Mg block.
采用膜片钳技术的全细胞模式，在细胞外钾离子浓度（[K⁺]ₒ）范围为4.5至160 mM的条件下，对牛肺动脉内皮细胞中的内向整流（IR）电流进行了研究。无论细胞内溶液中游离镁离子浓度（[Mg²⁺]ᵢ）是1.9 mM还是名义上为0，IR均表现出电压和时间依赖性门控。IR电导通过超极化激活，通过去极化失活。无论[Mg²⁺]ᵢ如何，在比钾离子反转电位（Eₖ）正约40 mV以上的电位范围内，均存在小的稳态外向IR电流。将其建模为平衡O门控过程中的一阶C，开放速率α和关闭速率β均呈指数依赖于电压，β对电压的依赖性更强，每变化9 mV变化一个e倍，而α每变化18 mV变化一个e倍。在所研究的所有[K⁺]ₒ范围内，α和β的电压依赖性随Eₖ移动，这是其他细胞中IR通道的特征。门控过程的稳态电压依赖性可用玻尔兹曼函数很好地描述。无论[Mg²⁺]ᵢ如何，在所有[K⁺]ₒ中，半激活电位平均比观察到的反转电位负约7 mV。使用无镁移液管溶液时，激活曲线稍陡（斜率因子为4.3 mV），而移液管中含有1.9 mM镁时（斜率因子为5.2 mV）。这些数据最简单的解释是，牛肺动脉内皮细胞中的IR通道具有一种内在的门控机制，并非由镁离子阻断引起。
