Hinrichsen R D, Saimi Y
J Physiol. 1984 Jun;351:397-410. doi: 10.1113/jphysiol.1984.sp015252.
The membrane properties of a new mutant of Paramecium tetraurelia, dancer, were compared under voltage clamp with those of the wild type. The Ca2+ current was isolated and examined using CsCl-filled electrodes and tetraethylammonium in the bath solution to block K+ channels. The amplitude of the Ca2+ transient was not altered by the mutation. However, the Ca2+ current in the mutant inactivated more slowly and less extensively: hence a larger sustained Ca2+ current remained in the mutant. A change in the time course of the deactivation of the Ba2+ current was observed in the mutant. This mutational change is not likely to be the consequence of the Ca2+-channel inactivation because it is seen in the Ba2+ solution where there is little inactivation of the current. Other measured properties of the Ca2+ channel, the voltage-dependent K+ current, and the resting properties of the membrane were normal in the mutant. The Ca2+-activated K+ current and the Ca2+-activated Na+ current were larger in the mutant than in the wild type, consistent with a greater elevation of free intracellular Ca2+ during depolarization in the mutant. It is likely that the mutation causes an alteration in the Ca2+-channel structure or in its immediate environment and thereby affects the inactivation and deactivation processes of the Ca2+ channel. As would be expected from the greater Ca2+ current, the mutant tends to generate all-or-none Ca action potentials as opposed to the graded action potentials in the wild type.
在电压钳制条件下，将四膜虫新突变体“舞者”的膜特性与野生型进行了比较。使用填充CsCl的电极并在浴液中加入四乙铵来阻断钾通道，从而分离并检测钙电流。钙瞬变的幅度并未因突变而改变。然而，突变体中的钙电流失活更慢且程度更小：因此突变体中保留了更大的持续钙电流。在突变体中观察到钡电流失活时间进程的变化。这种突变变化不太可能是钙通道失活的结果，因为在钡溶液中电流几乎没有失活的情况下也能看到这种变化。钙通道的其他测量特性、电压依赖性钾电流以及膜的静息特性在突变体中均正常。突变体中的钙激活钾电流和钙激活钠电流比野生型更大，这与突变体去极化期间细胞内游离钙的升高幅度更大一致。很可能该突变导致钙通道结构或其紧邻环境发生改变，从而影响钙通道的失活和去激活过程。正如从更大的钙电流所预期到的那样，与野生型的分级动作电位不同，突变体倾向于产生全或无的钙动作电位。
