Wang D, Armstrong D L
Laboratory of Signal Transduction, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709, USA.
J Physiol. 2000 Dec 15;529 Pt 3(Pt 3):699-705. doi: 10.1111/j.1469-7793.2000.00699.x.
The modulation of native muscarinic potassium channels (KACh) by tetraethylammonium (TEA) was studied at 35 degrees C in cell-free patches from acutely dissociated guinea-pig atrial myocytes. The channels were identified unambiguously by their conductance, inward rectification, rapid gating kinetics and pharmacological responses to muscarinic agonists and GTPgammaS. Addition of 5 mM TEA to the cytoplasmic side of the patches almost doubled the open probability of KACh channels that had been activated maximally by GTPgammaS. In contrast even 30 mM TEA did not significantly potentiate the response to carbachol in whole-cell recordings. Unlike GTPgammaS, TEA alone did not activate KACh channels de novo, but in patches that showed spontaneous KACh activity, 5 mM TEA increased channel open probability fourfold in the absence of added sodium, ATP or guanine nucleotides. Furthermore, the effect of TEA was not blocked by 10 uM atropine or by 1 mM GDPbetaS, and subsequent addition of 0.1 mM GTPgammaS did not stimulate channel activity further in the presence of TEA. Phosphatidylinositol 4,5-bisphosphate (PIP2) also stimulates KACh channels under these conditions, but the kinetics of gating differ from channels stimulated by either TEA or GTP, which are very similar to one another. The effects of TEA were not mimicked by tetramethyl- or tetrapentylammonium or by sodium or spermine, and TEA did not potentiate the activity of other inwardly rectifying potassium (KATP) channels in patches from cardiac myocytes. We consider the possibility that TEA is mimicking the effect of an unidentified cellular factor, not sodium or PIP2, which normally occupies the TEA site on KACh channel proteins but which diffuses away when the patch is excised.
在35摄氏度下，利用急性分离的豚鼠心房肌细胞的无细胞膜片，研究了四乙铵（TEA）对天然毒蕈碱钾通道（KACh）的调节作用。通过通道的电导、内向整流、快速门控动力学以及对毒蕈碱激动剂和GTPγS的药理学反应，明确鉴定了这些通道。向膜片的细胞质侧添加5 mM TEA，几乎使已被GTPγS最大程度激活的KACh通道的开放概率增加了一倍。相比之下，即使在全细胞记录中加入30 mM TEA，也不会显著增强对卡巴胆碱的反应。与GTPγS不同，单独的TEA不会从头激活KACh通道，但在显示自发KACh活性的膜片中，在不添加钠、ATP或鸟嘌呤核苷酸的情况下，5 mM TEA可使通道开放概率增加四倍。此外，TEA的作用不会被10 μM阿托品或1 mM GDPβS阻断，并且在存在TEA的情况下，随后添加0.1 mM GTPγS不会进一步刺激通道活性。在这些条件下，磷脂酰肌醇4,5-二磷酸（PIP2）也会刺激KACh通道，但门控动力学与由TEA或GTP刺激的通道不同，而TEA和GTP刺激的通道彼此非常相似。四甲基铵或四戊基铵、钠或精胺不会模拟TEA的作用，并且TEA不会增强心肌细胞膜片中其他内向整流钾（KATP）通道的活性。我们考虑了这样一种可能性，即TEA正在模拟一种未鉴定的细胞因子的作用，而不是钠或PIP2，该细胞因子通常占据KACh通道蛋白上的TEA位点，但在膜片切除时会扩散 away。 （原文最后“diffuses away”后表述不完整，按照准确内容翻译后这里有缺失）
