Castle N A, Fadous S R, Logothetis D E, Wang G K
Department of Anesthesia Research Laboratories, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115.
Mol Pharmacol. 1994 Dec;46(6):1175-81.
In the present study we have used two-electrode voltage-clamping of Xenopus oocytes expressing either Kv1.1 or Shaker B (ShB) delta 6-46 K+ channels to examine the effects of 4-aminopyridine (4-AP) on the process of slow inactivation. Neither of these channels exhibits fast inactivation. Channel activation was required for block by 4-AP in both channel types. In the absence of drug, inactivation of Kv1.1 and ShB delta 6-46 channels at 0 mV was biexponential [tau fast = 7.8 +/- 0.3 sec, tau slow = 33.9 +/- 0.9 sec, and Aslow/(Afast + Aslow) = 0.79 +/- 0.02 (n = 10) for Kv1.1 and tau fast = 3.5 +/- 0.4 sec, tau slow = 13.1 +/- 1.8 sec, and Aslow/(Afast + Aslow) = 0.35 +/- 0.06 (n = 3) for ShB delta 6-46]. In the presence of 4-AP, the rates of inactivation of Kv1.1 and ShB delta 6-46 were markedly slowed, resulting in a crossover phenomenon where, in the presence of drug, the outward current was smaller than control at the beginning of the depolarizing pulse but crossed over during the pulse to become larger than the control. The most obvious change induced by 0.2 mM 4-AP was a 2-fold slowing of the slow phase of inactivation [tau fast = 3.9 +/- 1.1 sec, tau slow = 67.1 +/- 3.6 sec, and Aslow/(Afast + Aslow) = 0.85 +/- 0.04 (n = 4) for Kv1.1 and tau fast = 3.5 +/- 0.4 sec, tau slow = 23.7 +/- 2.6 sec, and Aslow/(Afast + Aslow) = 0.75 +/- 0.02 (n = 3) for ShB delta 6-46, in the presence of 0.2 mM 4-AP]. In addition, there was a significant increase in the contribution of the slower phase of inactivation of ShB delta 6-46 channels in the presence of 4-AP. The slowed inactivation in the presence of 4-AP was accompanied by removal of 4-AP block. These results are consistent with the processes of 4-AP block and slow inactivation of Kv1.1 and ShB delta 6-46 channels being mutually exclusive.
在本研究中，我们对表达Kv1.1或Shaker B（ShB）δ6 - 46钾离子通道的非洲爪蟾卵母细胞进行双电极电压钳制，以研究4 - 氨基吡啶（4 - AP）对慢失活过程的影响。这两种通道均不表现出快失活。两种通道类型中，4 - AP的阻断都需要通道激活。在无药物情况下，Kv1.1和ShB δ6 - 46通道在0 mV时的失活是双指数的[对于Kv1.1，τ快速 = 7.8 ± 0.3秒，τ慢速 = 33.9 ± 0.9秒，且Aslow /(Afast + Aslow) = 0.79 ± 0.02（n = 10）；对于ShB δ6 - 46，τ快速 = 3.5 ± 0.4秒，τ慢速 = 13.1 ± 1.8秒，且Aslow /(Afast + Aslow) = 0.35 ± 0.06（n = 3）]。在4 - AP存在时，Kv1.1和ShB δ6 - 46的失活速率显著减慢，导致一种交叉现象，即在药物存在时，去极化脉冲开始时外向电流小于对照，但在脉冲期间交叉并变得大于对照。0.2 mM 4 - AP引起的最明显变化是失活慢相减慢2倍[对于Kv1.1，在0.2 mM 4 - AP存在时，τ快速 = 3.9 ± 1.1秒，τ慢速 = 67.1 ± 3.6秒，且Aslow /(Afast + Aslow) = 0.85 ± 0.04（n = 4）；对于ShB δ6 - 46，τ快速 = 3.5 ± 0.4秒，τ慢速 = 23.7 ± 2.6秒，且Aslow /(Afast + Aslow) = 0.75 ± 0.02（n = 3）]。此外，在4 - AP存在时，ShB δ6 - 46通道失活较慢相的贡献显著增加。4 - AP存在时失活减慢伴随着4 - AP阻断的解除。这些结果与4 - AP对Kv1.1和ShB δ6 - 46通道的阻断过程与慢失活相互排斥一致。
