Walsh K B, Arena J P, Kwok W M, Freeman L, Kass R S
Department of Physiology, School of Medicine and Dentistry, University of Rochester, New York 14680.
Am J Physiol. 1991 Apr;260(4 Pt 2):H1390-3. doi: 10.1152/ajpheart.1991.260.4.H1390.
When the patch-clamp technique was used, a slowly activating, time-dependent outward current was identified in both cell-attached and excised membrane patches obtained from guinea pig ventricular myocytes. This macroscopic patch current was present in approximately 50% of patches studied and could be observed both in the presence and absence of unitary single channel activity (i.e., ATP-sensitive K+ channels). The time course of activation of the patch current resembled that of the whole cell delayed-rectifier K+ current (IK) recorded under similar ionic conditions, and the patch current and IK were activated over a similar membrane potential range. The time-dependent patch current could be eliminated when the Nernst potential for K+ equaled that of the pulse voltage. The patch current was inhibited by external addition of the tertiary ammonium compound LY 97241 (50 microM) and was augmented after internal application of the catalytic subunit of adenosine 3',5'-cyclic monophosphate-dependent protein kinase (500 nM). Deactivating tail currents with kinetics similar to those of IK could be recorded to cell-attached and excised patches. Unitary single channel events underlying the time-dependent patch current could not be resolved despite various attempts to increase single channel conductance. Thus our results suggest that a major component of delayed rectification in guinea pig ventricular cells is due to the activity of a high-density, extremely low conductance K+ channel.
当使用膜片钳技术时，在从豚鼠心室肌细胞获得的细胞贴附式和膜片切除式膜片中均鉴定出一种缓慢激活、时间依赖性外向电流。这种宏观膜片电流存在于约50%的所研究膜片中，且在有和没有单一单通道活性（即ATP敏感性钾通道）的情况下均可观察到。膜片电流的激活时间进程类似于在相似离子条件下记录的全细胞延迟整流钾电流（IK）的激活时间进程，并且膜片电流和IK在相似的膜电位范围内被激活。当钾离子能斯特电位等于脉冲电压时，时间依赖性膜片电流可被消除。膜片电流受到外部添加叔铵化合物LY 97241（50微摩尔）的抑制，并且在内部应用3',5'-环磷酸腺苷依赖性蛋白激酶催化亚基（500纳摩尔）后增强。可记录到与IK动力学相似的失活尾电流至细胞贴附式和膜片切除式膜片。尽管进行了各种增加单通道电导的尝试，但仍无法分辨时间依赖性膜片电流背后的单一单通道事件。因此，我们的结果表明，豚鼠心室细胞延迟整流的一个主要成分是由于高密度、极低电导钾通道的活性。
