Meves H
Philos Trans R Soc Lond B Biol Sci. 1975 Jun 10;270(908):377-87. doi: 10.1098/rstb.1975.0017.
Voltage-clamp experiments were carried out on intracellularly perfused squid giant axons in a Na-free solution of 100 mM CaCl2+sucrose. The internal solution was 25 mM CsF+sucrose or 100 mM RbF+50mM tetraethylammonium chloride+sucrose. Depolarizing voltage clamp steps produced small inward currents; at large depolarizations the inward current reversed into an outward current. Tetrodotoxin completely blocked the inward current and part of the outward current. No inward current was seen with 100 mM MgCl2+sucrose as internal solution. It is concluded that the inward current is carried by Ca ions moving through the sodium channel. The reversal potential of the tetrodotoxin-sensitive current was +54mV with 25 mM CsF+sucrose inside and +10 mV with 100 mM RbF+50 mM tetraethylammonium chloride+sucrose inside. From the reversal potentials measured with varying external and internal solutions the relative permeabilities of the sodium channel for Ca, Cs and Na were calculated by means of the constant field equations. The results of the voltage-clamp experiments are compared with measurements of the Ca entry in intact axons.
在含有100 mM氯化钙和蔗糖的无钠溶液中，对细胞内灌注的枪乌贼巨大轴突进行电压钳实验。内部溶液为25 mM氟化铯和蔗糖或100 mM氟化铷、50 mM四乙铵氯化物和蔗糖。去极化电压钳步阶产生小的内向电流；在大的去极化时，内向电流反转成外向电流。河豚毒素完全阻断内向电流和部分外向电流。以100 mM氯化镁和蔗糖作为内部溶液时未观察到内向电流。得出的结论是，内向电流由通过钠通道移动的钙离子携带。当内部为25 mM氟化铯和蔗糖时，河豚毒素敏感电流的反转电位为+54 mV；当内部为100 mM氟化铷、50 mM四乙铵氯化物和蔗糖时，反转电位为+10 mV。根据用不同外部和内部溶液测得的反转电位，借助恒定场方程计算钠通道对钙、铯和钠的相对通透性。将电压钳实验结果与完整轴突中钙内流的测量结果进行比较。
