Panama Brian K, Lopatin Anatoli N
University of Michigan, Department of Molecular and Integrative Physiology, Ann Arbor, MI 48109-0622, USA.
J Physiol. 2006 Mar 1;571(Pt 2):287-302. doi: 10.1113/jphysiol.2005.097741. Epub 2005 Dec 22.
Recent studies have shown that Kir2 channels display differential sensitivity to intracellular polyamines, and have raised a number of questions about several properties of inward rectification important to the understanding of their physiological roles. In this study, we have carried out a detailed characterization of steady-state and kinetic properties of block of Kir2.1-3 channels by spermine. High-resolution recordings from outside-out patches showed that in all Kir2 channels current-voltage relationships display a 'crossover' effect upon change in extracellular K+. Experiments at different concentrations of spermine allowed for the characterization of two distinct shallow components of rectification, with the voltages for half-block negative (V1(1/2)) and positive (V2(1/2)) to the voltage of half-block for the major steep component of rectification (V0(1/2)). While V1(1/2) and V2(1/2) voltages differ significantly between Kir2 channels, they were coupled to each other according to the equation V1(1/2)-V2(1/2) = constant, strongly suggesting that similar structures may underlie both components. In Kir2.3 channels, the V2(1/2) was approximately 50 mV positive to V0(1/2), leading to a pattern of outward currents distinct from that of Kir2.1 and Kir2.2 channels. The effective valency of spermine block (Z0) was highest in Kir2.2 channels while the valencies in Kir2.1 and Kir2.3 channels were not significantly different. The voltage dependence of spermine unblock was similar in all Kir2 channels, but the rates of unblock were approximately 7-fold and approximately 16-fold slower in Kir2.3 channels than those in Kir2.1 and Kir2.2 when measured at high and physiological extracellular K+, respectively. In all Kir2 channels, the instantaneous phase of activation was present. The instantaneous phase was difficult to resolve at high extracellular K+ but it became evident and accounted for nearly 30-50% of the total current when recorded at physiological extracellular K+. In conclusion, the data are consistent with the universal mechanism of rectification in Kir2 channels, but also point to significant, and physiologically important, quantitative differences between Kir2 isoforms.
最近的研究表明，Kir2通道对细胞内多胺表现出不同的敏感性，并引发了一些关于内向整流的若干特性的问题，这些特性对于理解其生理作用很重要。在本研究中，我们对精胺阻断Kir2.1 - 3通道的稳态和动力学特性进行了详细表征。从外向型膜片进行的高分辨率记录表明，在所有Kir2通道中，电流 - 电压关系在细胞外K⁺变化时呈现“交叉”效应。在不同浓度精胺下进行的实验使得能够表征整流的两个不同的浅组分，其半阻断电压对于整流的主要陡峭组分的半阻断电压（V0(1/2)）为负（V1(1/2)）和正（V2(1/2)）。虽然Kir2通道之间的V1(1/2)和V2(1/2)电压有显著差异，但它们根据方程V1(1/2) - V2(1/2) =常数相互耦合，强烈表明相似的结构可能是这两个组分的基础。在Kir2.3通道中，V2(1/2)比V0(1/2)大约正50 mV，导致外向电流模式与Kir2.1和Kir2.2通道不同。精胺阻断的有效价（Z0）在Kir2.2通道中最高，而在Kir2.1和Kir2.3通道中的价没有显著差异。精胺解阻断的电压依赖性在所有Kir2通道中相似，但在高细胞外K⁺和生理细胞外K⁺下测量时，Kir2.3通道中的解阻断速率分别比Kir2.1和Kir2.2通道慢约7倍和约16倍。在所有Kir2通道中，存在激活的瞬时相。瞬时相在高细胞外K⁺时难以分辨，但在生理细胞外K⁺记录时变得明显，并占总电流的近30 - 50％。总之，数据与Kir2通道中整流的普遍机制一致，但也指出了Kir2亚型之间显著的、具有生理重要性的定量差异。
