Safronov B V, Vogel W
Physiologisches Institut, Justus-Liebig-Universitaet Giessen, Germany.
J Membr Biol. 1998 Mar 1;162(1):9-15. doi: 10.1007/s002329900337.
Properties of large conductance Ca(2+)-activated K+ channels were studied in the soma of motoneurones visually identified in thin slices of neonatal rat spinal cord. The channels had a conductance of 82 +/- 5 pS in external Ringer solution (5.6 mM Ko+/(/)155 mM Ki+) and 231 +/- 4 pS in external high-Ko solution (155 mM Ko+/(/)155 mM Ki+). The channels were activated by depolarization and by an increase in internal Ca2+ concentration. Potentials of half-maximum channel activation (E50) were -13, -34, -64 and -85 mV in the presence of 10(-6), 10(-5), 10(-4) and 10(-3) M internal Ca2+, respectively. Using an internal solution containing 10(-4) M Ca2+, averaged KCa currents showed fast activation within 2-3 msec after a voltage step to +50 mV. Averaged KCa currents did not inactivate during 400 msec voltage pulses. External TEA reduced the apparent single-channel amplitude with a 50% blocking concentration (IC50) of 0.17 +/- 0.02 mM. KCa channels were completely suppressed by externally applied 100 mM charybdotoxin. It is concluded that KCa channels activated by Ca2+ entry during the action potential play an important role in the excitability of motoneurones.
在新生大鼠脊髓薄片中通过视觉识别的运动神经元胞体中，研究了大电导钙激活钾通道的特性。在外部林格溶液（5.6 mM K⁺/155 mM K⁺）中，这些通道的电导为82±5 pS，在外部高钾溶液（155 mM K⁺/155 mM K⁺）中为231±4 pS。通道通过去极化和细胞内钙浓度的增加而被激活。在细胞内分别存在10⁻⁶、10⁻⁵、10⁻⁴和10⁻³ M钙的情况下，通道激活的半最大电位（E50）分别为-13、-34、-64和-85 mV。使用含有10⁻⁴ M钙的内部溶液，平均钙激活钾电流在电压阶跃到+50 mV后2 - 3毫秒内显示出快速激活。在400毫秒的电压脉冲期间，平均钙激活钾电流没有失活。外部四乙铵降低了表观单通道幅度，其50%阻断浓度（IC50）为0.17±0.02 mM。钙激活钾通道被外部施加的100 mM蝎毒素完全抑制。结论是，在动作电位期间由钙内流激活的钙激活钾通道在运动神经元的兴奋性中起重要作用。
