Ishihara K, Hiraoka M
Department of Cardiovascular Diseases, Tokyo Medical and Dental University, Japan.
J Membr Biol. 1994 Oct;142(1):55-64. doi: 10.1007/BF00233383.
The complementary DNA encoding the inward rectifier potassium channel was cloned from the adult mouse heart by using the polymerase chain reaction. The clone had the nucleotide sequence identical to that of the IRK1 gene cloned from a mouse macrophage cell line. Northern blot analysis revealed that the transcript of this gene was mainly expressed in the ventricle, where the inward rectifier K+ channel plays a predominant role in maintaining the high negative value of the resting membrane potential. The current expressed by injection of the complementary RNA of the cloned gene into Xenopus oocytes showed a marked inward rectification that depends on the driving force of K+. A region of negative slope conductance was observed in the current-voltage relationship at potentials positive to the reversal potential. When the extracellular K+ concentration was raised, the increase in outward current amplitude resulted in the "crossover" of outward current-voltage relations. The fast time-dependent increase in current amplitude was recorded upon membrane repolarization from a potential positive to the reversal potential. The kinetics of the time-dependent current was very similar to that of the intrinsic gating mechanism of the native cardiac inward rectifier K+ channel. Our results suggest the existence of the intrinsic gating mechanism, accounting for the extent of rectification in the current-voltage relationship in the expressed channel.
利用聚合酶链反应从成年小鼠心脏中克隆出编码内向整流钾通道的互补DNA。该克隆体的核苷酸序列与从小鼠巨噬细胞系克隆出的IRK1基因的序列相同。Northern印迹分析显示，该基因的转录本主要在心室中表达，在心室中内向整流K⁺通道在维持静息膜电位的高负值方面起主要作用。将克隆基因的互补RNA注射到非洲爪蟾卵母细胞中所表达的电流显示出明显的内向整流，这取决于K⁺的驱动力。在高于反转电位的电位下，电流-电压关系中观察到负斜率电导区域。当细胞外K⁺浓度升高时，外向电流幅度的增加导致外向电流-电压关系的“交叉”。在膜从高于反转电位的电位复极化时记录到电流幅度随时间快速增加。时间依赖性电流的动力学与天然心脏内向整流K⁺通道的固有门控机制非常相似。我们的结果表明存在固有门控机制，这解释了所表达通道中电流-电压关系的整流程度。
