Acetylcholine receptor: evidence for a voltage-dependent regulatory site for acetylcholine. Chemical kinetic measurements in membrane vesicles using a voltage clamp.
Acetylcholine receptor: evidence for a voltage-dependent regulatory site for acetylcholine. Chemical kinetic measurements in membrane vesicles using a voltage clamp.
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乙酰胆碱受体：乙酰胆碱电压依赖性调节位点的证据。
DOI：
10.1021/bi00294a042
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发表时间：
1983
期刊：
影响因子：
2.9
通讯作者：
G. P. Hess
中科院分区：
文献类型：
--
作者：
K. Takeyasu;J. Udgaonkar;G. P. Hess
在电压箝位条件下，利用猝流技术研究了由电鳗制备的膜囊中乙酰胆碱受体介导的离子易位，该技术可以在毫秒到秒的时间范围内测量易位。在500倍的乙酰胆碱浓度范围内，在-45 mV的跨膜电压Vm， pH 7.0, 1℃下测量两个速率系数。JA是在没有失活（脱敏）的情况下，受体激活状态下离子转运的速率系数，alpha是乙酰胆碱使受体失活的速率系数。(1)当乙酰胆碱浓度达到300微米时，JA和α随乙酰胆碱浓度的增加而增加。在较高的浓度下，观察到离子通量率的浓度依赖性降低，而不伴随失活率的变化。这种抑制作用以前没有报道过，在没有跨膜电压的情况下，乙酰胆碱或氨基甲酰胆碱也没有观察到。(2)最大流入速率系数为26 s-1，约为0 mV时的两倍[JA(max) = 15 s-1]。这与先前的解释一致，即JA（max）值与通道开放平衡常数1/phi，以及1/phi与肌肉细胞中开放受体通道的平均寿命的关系，这取决于Vm。(3)观察到的最大失活率系数[α (max) = 8.5 s-1]略大于0 mV时的失活率系数[α (max) = 5 s-1]。（摘要删节250字）
Acetylcholine receptor mediated ion translocation in membrane vesicles prepared from the Electrophorus electricus electroplax was investigated under voltage clamp conditions by using a quench-flow technique that allows the translocation to be measured in the millisecond to second time region. Two rate coefficients were measured over a 500-fold concentration range of acetylcholine, at a transmembrane voltage, Vm, of -45 mV, at pH 7.0, 1 degrees C. JA is the rate coefficient for ion translocation by the active state of the receptor in the absence of inactivation (desensitization), and alpha is the rate coefficient for the inactivation of the receptor by acetylcholine. (1) The values of JA and alpha increase with increasing acetylcholine concentration up to 300 microM. At higher concentrations, a concentration-dependent decrease in the ion flux rate was observed without a concomitant change in the inactivation rate. This inhibitory effect has not been reported previously and was not observed with acetylcholine or carbamoylcholine in the absence of a transmembrane voltage. (2) The value of the maximum influx rate coefficient, 26 s-1, is approximately twice that observed at 0 mV [JA(max) = 15 s-1]. This is consistent with previous interpretations that related JA(max) values to the channel-opening equilibrium constant, 1/phi, and with the relation of 1/phi to the mean lifetime of the open receptor channel in muscle cells, which is dependent on Vm. (3) The maximum observed inactivation rate coefficient [alpha(max) = 8.5 s-1] is somewhat larger than that observed at 0 mV [alpha(max) = 5 s-1].(ABSTRACT TRUNCATED AT 250 WORDS)