Horie M, Irisawa H
Am J Physiol. 1987 Jul;253(1 Pt 2):H210-4. doi: 10.1152/ajpheart.1987.253.1.H210.
Rectifying properties of the acetylcholine (ACh)-sensitive K+ channels were studied using a patch-clamp method in single atrial cells prepared enzymatically from adult guinea pig hearts. In the presence of micromolar concentration of nonhydrolyzable guanosine 5'-triphosphate (GTP) analogue 5'-guanylylimidodiphosphate (GppNHp) and the absence of Mg2+ at the inner surface of patch membrane [( Mg2+]i), the channel activity recovered in inside-out patch condition. The single channel conductance became ohmic between -80 and +80 mV (symmetrical 150 mM K+ solutions). The rapid relaxation of outward single channel currents was disclosed on a depolarization. [Mg2+]i blocked the outward current through the channel dose- and voltage-dependently and also induced a dose-dependent increase in the channel activation. The apparent paradoxical role of [Mg2+]i is important for the cholinergic control in the heart; voltage-dependent Mg block ensures a low K+ conductance of cell membrane at the plateau of action potentials during the exposure to ACh, thereby slowing the heart rate without unfavorable shortening of the action potentials.
采用膜片钳方法，在酶解分离的成年豚鼠心脏单个心房细胞中研究了乙酰胆碱（ACh）敏感钾通道的整流特性。在膜片内表面微摩尔浓度的非水解性鸟苷5'-三磷酸（GTP）类似物5'-鸟苷酰亚胺二磷酸（GppNHp）存在且无Mg2+（[Mg2+]i）的情况下，通道活性在膜片外翻条件下恢复。在 -80至 +80 mV之间（对称的150 mM K+溶液），单通道电导呈线性。去极化时可观察到外向单通道电流的快速松弛。[Mg2+]i剂量和电压依赖性地阻断通过该通道的外向电流，并且还诱导通道激活的剂量依赖性增加。[Mg2+]i这种明显矛盾的作用对心脏的胆碱能控制很重要；电压依赖性Mg阻断可确保在暴露于ACh期间动作电位平台期细胞膜的低K+电导，从而减慢心率而不会不利地缩短动作电位。
