THE CALCIUM-INDEPENDENT TRANSIENT OUTWARD POTASSIUM CURRENT IN ISOLATED FERRET RIGHT VENTRICULAR MYOCYTES .2. CLOSED STATE REVERSE USE-DEPENDENT BLOCK BY 4-AMINOPYRIDINE
THE CALCIUM-INDEPENDENT TRANSIENT OUTWARD POTASSIUM CURRENT IN ISOLATED FERRET RIGHT VENTRICULAR MYOCYTES .2. CLOSED STATE REVERSE USE-DEPENDENT BLOCK BY 4-AMINOPYRIDINE
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DOI：
10.1085/jgp.101.4.603
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发表时间：
1993-04-01
影响因子：
3.8
通讯作者：
STRAUSS, HC
中科院分区：
文献类型：
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作者：
CAMPBELL, DL;QU, YH;STRAUSS, HC
用全细胞膜片钳技术研究了4-氨基吡啶(4-AP)对雪貂右室肌细胞钙非依赖性瞬时外向钾电流I(TO)的阻断作用。4-AP通过一种封闭状态的阻断机制降低I(TO)，该机制表现出“反向使用依赖”的行为，其推断如下：(A)在超极化电位下形成紧张性阻滞剂；(B)在去极化电位处抑制紧张性阻滞剂的形成；(C)在去极化电位处出现峰电流延迟的“交叉现象”；(D)去极化电位阻断的解除，这与低浓度4-AP的稳态失活(0.1 mM4-AP的V1/2几乎等于-10 mV)和较高浓度的稳态激活(1 mM4-AP的V1/2=+7 mV，10 mM4=AP的+15 mV)平行；以及(E)4-AP在超极化电位下的重新电离。在0.5-1.0 mM的4-AP存在下，通过恢复和失活动力学的测定，未发现4-AP与I(TO)通道的开放或失活状态相互作用的证据。在超极化电位(-30~-90 mV)下，10 mM 4-AP与通道的闭合状态(表观K(D)几乎等于-0.2 mM)联系缓慢(时间常数约为800~1300ms)。从-90 mV到-20 mV，I(TO)通道对4-AP的亲和力似乎是电压不敏感的；然而，在去极化电位(+20到+100 mV)时，4-AP以大约350到150毫秒的时间常数解离。因此，4-AP与I(TO)通道结合的性质在发生通道激活和失活的电位范围内经历转变(-30 mV到+20 mV)。我们提出了I(TO)通道门控和4-AP结合动力学的封闭状态模型，其中4-AP结合到三个封闭状态。在该模型中，随着通道接近开放状态，4-AP的亲和力逐渐降低，但没有固有的电压依赖性结合。
Block of the calcium-independent transient outward K+ current, I(to), by 4-aminopyridine (4-AP) was studied in ferret right ventricular myocytes using the whole cell patch clamp technique. 4-AP reduces I(to) through a closed state blocking mechanism displaying ''reverse use-dependent'' behavior that was inferred from: (a) development of tonic block at hyperpolarized potentials; (b) inhibition of development of tonic block at depolarized potentials; (c) appearance of ''crossover phenomena'' in which the peak current is delayed in the presence of 4-AP at depolarized potentials; (d) relief of block at depolarized potentials which is concentration dependent and parallels steady-state inactivation for low 4-AP concentrations (V1/2 almost-equal-to -10 mV in 0.1 mM 4-AP) and steady-state activation at higher concentrations (V1/2 = +7 mV in 1 mM 4-AP, +15 mV in 10 mM 4=AP); and (e) reassociation of 4-AP at hyperpolarized potentials. No evidence for interaction of 4-AP with either the open or inactivated state of the I(to) channel was obtained from measurements of kinetics of recovery and deactivation in the presence of 0.5-1.0 mM 4-AP. At hyperpolarized potentials (-30 to -90 mV) 10 mM 4-AP associates slowly (time constants ranging from approximately 800 to 1,300 ms) with the closed states of the channel (apparent K(d) almost-equal-to 0.2 mM). From -90 to -20 mV the affinity of the I(to) channel for 4-AP appears to be voltage insensitive; however, at depolarized potentials (+20 to +100 mV) 4-AP dissociates with time constants ranging from approximately 350 to 150 ms. Consequently, the properties of 4-AP binding to the I(to) channel undergo a transition in the range of potentials over which channel activation and inactivation occurs (-30 to +20 mV). We propose a closed state model of I(to) channel gating and 4-AP binding kinetics, in which 4-AP binds to three closed states. In this model 4-AP has a progressively lower affinity as the channel approaches the open state, but has no intrinsic voltage dependence of binding.