EFFECT OF MEMBRANE-POTENTIAL ON ACETYLCHOLINE-INDUCED INWARD CURRENT IN GUINEA-PIG ILEUM
EFFECT OF MEMBRANE-POTENTIAL ON ACETYLCHOLINE-INDUCED INWARD CURRENT IN GUINEA-PIG ILEUM
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DOI：
10.1113/jphysiol.1990.sp018055
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发表时间：
1990-05-01
影响因子：
5.5
通讯作者：
ISENBERG, G
中科院分区：
文献类型：
--
作者：
INOUE, R;ISENBERG, G
1.应用门冬氨酸铯内溶液全细胞膜片钳技术，观察了乙酰胆碱（ACh）诱发的豚鼠回肠纵行肌层单个细胞内向电流的电压依赖性门控。2.在电压钳实验中，在-80至-30 mV的保持电位下，ACh（300 μ m）在生理盐浴溶液（PSS）中产生缓慢的持续内向电流。用其他一价和二价阳离子取代Na+的反转电位测量表明，该电流是通过非选择性阳离子通道（Ins、ACh）。在超极化过程中，Ins，ACh的幅度瞬间增加，然后放松到一个新的稳态水平。瞬时峰的I-V关系与翻转电位为0 mV呈线性关系，稳态时呈钟形关系。松弛的时间过程似乎是单指数的，其时间常数降低较强的超极化。4.这些结果不受有机Ca 2+拮抗剂D 600或尼群地平（10 μ m）的影响。在此条件下，Ins、ACh在0 mV时的最大弦电导约为1.5nS。稳态激活关系用Boltzmann方程很好地拟合，在膜电位负至0 mV时，半最大激活（Vh）为-50 mV，斜率因子（k）为-15 mV，但超过0 mV，激活程度再次降低。松弛的时间常数也似乎遵循S形曲线。5.在电流钳实验中，ACh（300 μ m）的灌流使膜去极化至-10至0 mV。内向电流引起的膜中度超极化（-70 ~-80mV）减弱ACh引起的去极化，而更强的超极化（<-80mV）则可消除ACh引起的去极化。这些结果表明，ACh引起的去极化受膜电位控制，这可以用Ins、ACh的电压依赖性gting来解释。
1. The whole-cell patch clamp technique with caesium aspartate internal solution was used with single isolated cells from the longitudinal muscle layer of guinea pig ileum, to investigate the voltage-dependent gating of ACh-induced inward current. 2. In voltage clamp experiments, at holding potentials ranging from -80 to -30 mV, ACh (300 .mu.m) produced a slow sustained inward current in physiological salt bath solution (PSS). The measurements of the reversal potentials on substituting Na+ by other monovalent and divalent cations showed that this current is through non-selective cation channels (Ins,ACh). During hyperpolarizations, Ins,ACh instantaneously increased in amplitude and then relaxed to a new steady-state level. The I-V relationship of the instantaneous peak was linear with a reversal potential of 0 mV, while that of the steady state was bell-shaped. The time course of relaxation appeared to be monoexponential and its time constants were reduced by stronger hyperpolarizations. 4. These results were not affected by the organic Ca2+ antagonists D600 or nitrendipine (10 .mu.m). Under this condition, maximal chord conductance of Ins,ACh which was observed at 0 mV was about 1.5 nS. The steady-state activation relationship was well fitted by Boltzmann''s equation with a half-maximal activation (Vh) of -50 mV and a slope factor (k) of -15 mV at membrane potentials negative to 0 mV, but over 0 mV the degree of activation was again decreased. The time constants for relaxation also appeared to follow a sigmoid curve. 5. In current clamp experiments, superfusion of ACh (300 .mu.m) depolarized the memebrane up to -10 to 0 mV. Inward current injection resulting in the moderate hyperpolarization of the membrane (-70 to -80 mV) attenuated ACh-induced depolarization and stronger hyperpolarization (< -80 mV) abolished it. 6. These results show that ACh-induced depolarization is controlled by the membrane potential, which is explained by the voltage-dependent gting of Ins,ACh.