Miniature end-plate currents (m.e.p.c.s) and acetylcholine induced current noise were recorded from the cutaneous pectoris muscle of the frog with the voltage-clamp technique. Analysis of current noise was used to estimate mean single channel current and the mean lifetime of an open channel. 2. Adding Ni2+ or Ca2+ to the bathing solution reduced the amplitude of the m.e.p.c.s. Ten mM-Ni2+ decreased the amplitude 64%, while raising Ca2+ from 2 to 10mM decreased the amplitude 35%. 3. The decreased amplitude of the m.e.p.c. in Ni2+ and increased Ca2+ can be explained by a decrease in single channel current. Ten mM-Ni2+ decreased mean single channel current 64% while raising Ca2+ from 2 to 10 mM decreased single channel current 28%. 4. The decrease in single channel current was due to a decrease in the driving potential and single channel conductance. Ten mM-Ni2+ and Ca2+ shifted the reversal potential for the m.e.p.c. about 10 mV negative from the control value of -4.6 mV; at the same time single channel conductance was decreased 59% in Ni2+ and 18% in increased Ca2+. 5. In contrast to the similar direction of effects of Ni2+ and Ca2+ on m.e.p.c. amplitude, reversal potential, and single channel conductance, Ni2+ and Ca2+ had different effects on m.e.p.c. time course. Ten mM-Ni2+ increased the time constant of m.e.p.c. decay 80% while raising Ca2+ from 2 to 10 mM decreased the time constant of decay 17%. 6. Ni2+ and Ca2+ also had different effects on single channel lifetimes. Ten mM-Ni2+ increased channel lifetime about 50%, while raising Ca2+ from 2 to 10 mM did not significantly affect channel lifetime. 7. These results suggest that changes in single channel lifetime and conductance due to ionic influences are not necessarily tightly coupled. The results also suggest that the effects of both Ni2+ and Ca2+ on channel lifetime cannot be accounted for in terms of a simple surface potential hypothesis.
摘要
采用电压钳技术，从青蛙的胸皮肌记录微小终板电流（m.e.p.c.s）和乙酰胆碱诱发的电流噪声。通过对电流噪声的分析来估计平均单通道电流和开放通道的平均寿命。2. 向灌流液中添加Ni2+或Ca2+会降低m.e.p.c.s的幅度。10 mM - Ni2+使幅度降低64%，而将Ca2+从2 mM提高到10 mM使幅度降低35%。3. Ni2+存在时m.e.p.c.幅度降低以及Ca2+浓度升高时m.e.p.c.幅度降低，可通过单通道电流的降低来解释。10 mM - Ni2+使平均单通道电流降低64%，而将Ca2+从2 mM提高到10 mM使单通道电流降低28%。4. 单通道电流的降低是由于驱动电位和单通道电导的降低。10 mM - Ni2+和Ca2+使m.e.p.c.的反转电位从对照值 - 4.6 mV向负方向移动约10 mV；同时，Ni2+存在时单通道电导降低59%，Ca2+浓度升高时单通道电导降低18%。5. 与Ni2+和Ca2+对m.e.p.c.幅度、反转电位和单通道电导的影响方向相似形成对比的是，Ni2+和Ca2+对m.e.p.c.的时间进程有不同影响。10 mM - Ni2+使m.e.p.c.衰减的时间常数增加80%，而将Ca2+从2 mM提高到10 mM使衰减的时间常数降低17%。6. Ni2+和Ca2+对单通道寿命也有不同影响。10 mM - Ni2+使通道寿命增加约50%，而将Ca2+从2 mM提高到10 mM对通道寿命没有显著影响。7. 这些结果表明，离子影响导致的单通道寿命和电导变化不一定紧密相关。结果还表明，Ni2+和Ca2+对通道寿命的影响不能用简单的表面电位假说来解释。
