Aleksandrov A, Velimirovic B, Clapham D E
Department of Pharmacology, Mayo Foundation, Rochester, Minnesota 55905, USA.
Biophys J. 1996 Jun;70(6):2680-7. doi: 10.1016/S0006-3495(96)79837-5.
Inwardly rectifying potassium (K+) channels (IRK1) were incorporated into lipid bilayers to test the relative contributions of various mechanisms to inward rectification. IRK1 channels were expressed in Xenopus laevis oocytes and oocyte membrane vesicles containing the channels were fused with lipid bilayers. The major properties of the IRK1 channel were similar whether measured in the oocyte membrane or lipid bilayer; the single channel conductance was 21 pS in 140 mM symmetrical [K+] and varied as a square root of external [K+]. Importantly, IRK1 channels display voltage-dependent inward rectification in the absence of divalent ions or charged regulators such as spermine, indicating that they possess an intrinsic rectification mechanism. Although rectification was significantly increased by either Mg2+ or spermine added to the cytoplasmic face of the channel, their effects could not be explained by simple block of the open pore. The Hille and Schwartz (1978) model, originally proposed to explain inward rectification by singly charged blocking particles, cannot be used to explain rectification by multiply charged blocking particles. As an alternative, we propose that in addition to a slow gating mechanism producing long lasting open and closed states, there is a distinct, intrinsic fast gating process amplified by cytoplasmic Mg2+ and/or polyamine binding to the channel.
内向整流钾（K+）通道（IRK1）被整合到脂质双分子层中，以测试各种机制对内向整流的相对贡献。IRK1通道在非洲爪蟾卵母细胞中表达，含有这些通道的卵母细胞膜囊泡与脂质双分子层融合。无论在卵母细胞膜还是脂质双分子层中测量，IRK1通道的主要特性都相似；在140 mM对称[K+]中，单通道电导为21 pS，并随外部[K+]的平方根变化。重要的是，IRK1通道在没有二价离子或诸如精胺等带电调节剂的情况下表现出电压依赖性内向整流，这表明它们具有内在的整流机制。尽管通过向通道胞质面添加Mg2+或精胺可显著增强整流，但它们的作用不能用简单的开放孔道阻断来解释。最初提出用于解释单电荷阻断颗粒引起的内向整流的希勒和施瓦茨（1978）模型，不能用于解释多电荷阻断颗粒引起的整流。作为一种替代方案，我们提出，除了产生持久开放和关闭状态的缓慢门控机制外，还存在一种独特的、内在的快速门控过程，该过程通过胞质Mg2+和/或多胺与通道结合而放大。
