ACETYLCHOLINE-SENSITIVE MUSCARINIC K+ CHANNELS IN MAMMALIAN VENTRICULAR MYOCYTES
ACETYLCHOLINE-SENSITIVE MUSCARINIC K+ CHANNELS IN MAMMALIAN VENTRICULAR MYOCYTES
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DOI：
10.1152/ajpheart.1994.266.5.h1812
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发表时间：
1994-05-01
影响因子：
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通讯作者：
WASSERSTROM, JA
中科院分区：
文献类型：
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作者：
KOUMI, SI;WASSERSTROM, JA
已知乙酰胆碱（ACh）可增加心房和心脏起搏器组织的钾离子传导。这种效应在哺乳动物心室组织中尚未得到很好的界定。我们使用膜片钳技术在分离的人、猫和豚鼠心室肌细胞中鉴定并表征了乙酰胆碱敏感的毒菌碱K+通道[I-K(ACh)]活性。应用乙酰胆碱可增加人心室肌细胞的全细胞膜电流。ach感应电流在心室呈内整流，其斜率电导小于心房。在细胞贴附的单通道记录中，当ACh包含在溶液中时，观察到I-K（ACh）的活性。该通道的斜率电导为43 +/- 2 pS，打开时间按单一指数函数分布，平均打开寿命为1.8 +/- 0.3 ms。该通道具有与人类心房I-K（ACh）相似的电导和动力学特征，其斜率电导为43 +/- 3ps，平均打开寿命为1.6 +/- 0.3 ms。而心室通道半最大刺激时ACh浓度（K-D = 0.13 μ M）高于心房通道（K-D = 0.03 μ M）。腺苷引起了相同的K+通道的激活。在形成一个由内向外切除的斑块后，通道活动消失。在溶液中应用GTP （100 μ M）或GTP γ S （100 μ M）引起通道重新激活。当肌细胞与百日咳毒素（PTX）预孵育时，ACh未能激活这些通道，这表明PTX敏感的G蛋白G(i)对于激活i - k （ACh）至关重要。在猫和豚鼠心室肌细胞中也发现了I-K（ACh）通道的活性。我们得出的结论是，ACh通过Gi直接激活哺乳动物心室肌细胞中的I-K(ACh)，其方式与心房肌细胞几乎相同。
Acetylcholine (ACh) is known to increase K+ conductance in the atrium and in pacemaker tissues in the heart. This effect has not been well defined in mammalian ventricular tissues. We have identified and characterized the ACh-sensitive muscarinic K+ channel [I-K(ACh)] activity in isolated human, cat, and guinea pig ventricular myocytes using the patch-clamp technique. Application ofACh increased whole cell membrane current in human ventricular myocytes. Current-voltage relationship of the ACh-induced current in ventricle exhibited inward-rectification whose slope conductance was smaller than that in atrium. In single-channel recording from cell-attached patches, I-K(ACh) activity was observed when ACh was included in the solution. The channel exhibited a slope conductance of 43 +/- 2 pS. Open times were distributed according to a single exponential function with mean open lifetime of 1.8 +/- 0.3 ms. The channel had conductance and kinetic characteristics similar to human atrial I-K(ACh), which had a slope conductance of 43 +/- 3 pS and mean open lifetime of 1.6 +/- 0.3 ms. However, concentration of ACh at half-maximal stimulation (K-D) of the channel in ventricle was greater (K-D = 0.13 mu M) than that in atrium (K-D = 0.03 mu M). Adenosine caused activation of the same K+ channel. After formation of an excised inside-out patch, channel activity disappeared. Application of GTP (100 mu M) or GTP gamma S (100 mu M) to the solution caused reactivation of the channel. When myocytes were preincubated with pertussis toxin (PTX), ACh failed to activate these channels, indicating that the PTX-sensitive G protein, G(i), is essential for activation of I-K(ACh). I-K(ACh) channel activity was also found in cat and guinea pig ventricular myocytes. We conclude that ACh directly activates the I-K(ACh) in mammalian ventricular myocytes via Gi in a fashion almost identical to atrial myocytes.