Studies of the unitary properties of adenosine‐5'‐triphosphate‐regulated potassium channels of frog skeletal muscle.
Studies of the unitary properties of adenosine‐5'‐triphosphate‐regulated potassium channels of frog skeletal muscle.
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青蛙骨骼肌腺苷-5-三磷酸调节钾通道单一特性的研究。
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发表时间：
1987
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通讯作者：
P. Stanfield
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作者：
A. Spruce;N. Standen;P. Stanfield
1. 使用膜片钳技术研究青蛙骨骼肌肌膜囊泡中 5'-三磷酸腺苷 (ATP) 依赖性 K+ 通道。除了 ATP 依赖性之外，这些通道的打开还依赖于电压，打开状态概率 (P open) 随着去极化而增加。 2. 如果 Na-K 渗透率比 (pNa/pK) 等于 0.015，则单一电流的反转电势随外部 K+ 浓度 [K+]o 的变化而变化，正如预期的那样。随着 [K+]o 的增加，单位电导也增加，从 2.5 mM-K+ 中的 14.8 +/- 0.5 pS (n = 5) 增加到 60 mM-K+ 中的 42.3 +/- 1.0 pS (n = 8)。这一增幅低于独立后的预期。 3. 用 60 mM-外部 Rb+ 替换 60 mM-外部 K+，使单一电流的反转电位移动了 ‐6.7 mV，表明 Rb+ 几乎与 K+ 一样容易进入通道（Rb-K 渗透率比，pRb/pK = 0.76）。 Rb+ 的单一电流要小得多，这与通道内 Rb+ 的结合一致。 4. ATP 调节的 K+ 通道被内部和外部四乙铵离子 (TEA+) 阻断。 2 mM-TEA+，应用于膜片的细胞质面，中断通道开口。较高的浓度降低了单一电流幅度，表明 TEA+ 阻断的速度增加。 5. ATP 导致的 P open 减少与 1:1 结合和 0.135 mM 解离常数一致。 ATP 似乎不会被水解而关闭通道。 5'-二磷酸腺苷 (ADP) 和 5'-单磷酸腺苷 (AMP) 的效果不如 ATP，但保留了通道关闭特性。用其他嘌呤或嘧啶碱基取代腺嘌呤会显着降低活性，就像用 2'-脱氧核糖或核糖 2',3'-二醛取代核糖一样。 6.肌浆Ca2+不影响P开放。 7. 从新生大鼠大腿肌肉中长出的肌管似乎缺乏 ATP 依赖性 K+ 通道。成年青蛙肌肉似乎缺乏高电导 Ca2+ 依赖性 K+ 通道，至少在表面膜上是如此。在肌管膜中发现了这种通道。 8. 构建了打开和关闭时间直方图，并且与至少两个打开状态和至少三个关闭状态一致。通道开口以突发方式分组。 ATP 减少了开放时间、突发长度和每次突发的开放数量。 9. 根据简单的艾林速率理论公式讨论了 [K+]o 对单一电导的影响以及用 Rb+ 替换 K+ 的影响。（摘要截断为 400 字）
1. Patch‐clamp techniques were used to study adenosine‐5'‐triphosphate (ATP)‐dependent K+ channels in sarcolemmal vesicles from frog skeletal muscle. In addition to its ATP dependence, opening of these channels was voltage dependent, the open‐state probability (P open) increasing with depolarization. 2. The reversal potential of unitary currents changed with external K+ concentration, [K+]o, as expected if the Na‐K permeability ration (pNa/pK) equals 0.015. Unitary conductance increased with increasing [K+]o from 14.8 +/‐ 0.5 pS (n = 5) in 2.5 mM‐K+ to 42.3 +/‐ 1.0 pS (n = 8) in 60 mM‐K+. This increase was less than that expected from independence. 3. Replacement of 60 mM‐external K+ by 60 mM‐external Rb+ shifted the reversal potential of unitary currents by ‐6.7 mV, suggesting that Rb+ enters channels nearly as easily as does K+ (Rb‐K permeability ration, pRb/pK = 0.76). Unitary currents were much smaller in Rb+, consistent with Rb+ binding within the channel. 4. The ATP‐regulated K+ channel was blocked by both internal and external tetraethylammonium ions (TEA+). 2 mM‐TEA+, applied to the cytoplasmic face of membrane patches, interrupted channel openings. Higher concentrations reduced unitary current amplitude, suggesting an increase in the rapidity of TEA+ block. 5. The reduction in P open by ATP was consistent with 1:1 binding and a dissociation constant of 0.135 mM. ATP appeared not to be hydrolysed to close channels. Adenosine 5'‐diphosphate (ADP) and adenosine 5'‐monophosphate (AMP) were less effective than ATP, but retained channel closing properties. Substitution of adenine with other purines or with pyrimidine bases substantially reduced activity, as did substitution of ribose by 2'‐deoxyribose or by ribose 2',3'‐dialdehyde. 6. Sarcoplasmic Ca2+ did not influence P open. 7. Myotubes, grown from thigh muscles of new‐born rats, appeared to lack ATP‐dependent K+ channels. Adult frog muscle appeared to lack high‐conductance Ca2+‐dependent K+ channels, at least in the surface membrane. Such channels were found in myotube membranes. 8. Open‐ and closed‐time histograms were constructed and were consistent with at least two open and at least three closed states. Channel openings were grouped in bursts. Open times, burst lengths and the number of openings per burst were reduced by ATP. 9. The effects of [K+]o on unitary conductance and of K+ replacement with Rb+ are discussed in terms of a simple Eyring rate theory formulation.(ABSTRACT TRUNCATED AT 400 WORDS)