Matsuda H
Department of Physiology, Kansai Medical University, Moriguchi, Osaka 570, Japan.
Pflugers Arch. 1996 May;432(1):26-33. doi: 10.1007/s004240050101.
Rb+ and Cs+ ion permeability and the effects of these ions from the inside on the inwardly rectifying K+ channel were studied in guinea-pig ventricular cells. A total substitution of either Rb+ or Cs+ for external K+ in the outside-out configuration of the patch-clamp technique abolished the inward current. The outward current carried by K+ was recorded. The unitary amplitude was reduced to about half of the control value with Rb+ but was not changed with Cs+. Internal Rb+ and Cs+, at a concentration of 10-40 mM, reduced the unitary amplitude of the outward current. No substate behaviour was observed. The reversal potential was +18 mV after replacing 105 mM internal K+ with Rb+ at 150 mM external K+. This value gives a permeability ratio of Rb+ to K+ of 0.27. Under a total substitution of Rb+ or Cs+ for internal K+, the outward currents were not measurable. Cs+ induced flickering in the inward current carried by K+. It is thus concluded that Rb+ and Cs+ ions are not measurably permeant at the single-channel level but permit K+ permeation in place of external K+ and that internal Rb+ and Cs+ produce a voltage-dependent block of the channel with fast kinetics.
在豚鼠心室肌细胞中研究了铷离子（Rb⁺）和铯离子（Cs⁺）的通透性以及这些离子从细胞内侧对内向整流钾通道的影响。在膜片钳技术的外翻式配置中，用Rb⁺或Cs⁺完全替代外部钾离子可消除内向电流。记录了由钾离子携带的外向电流。Rb⁺使单位电流幅度降低至对照值的约一半，但Cs⁺对其无影响。浓度为10 - 40 mM的内部Rb⁺和Cs⁺降低了外向电流的单位幅度。未观察到亚态行为。在外部钾离子浓度为150 mM时，用150 mM的Rb⁺替代105 mM的内部钾离子后，反转电位为 +18 mV。该值给出Rb⁺与K⁺的通透率为0.27。在用Rb⁺或Cs⁺完全替代内部钾离子的情况下，外向电流无法测量。Cs⁺导致钾离子携带的内向电流出现闪烁。因此得出结论，在单通道水平上，Rb⁺和Cs⁺离子的通透性不可测量，但可替代外部钾离子允许钾离子通透，并且内部Rb⁺和Cs⁺以快速动力学产生电压依赖性通道阻滞。
