Der spannungsabhängige Einwärtsstrom von $\underline{Paramecium}$ caudatum (Ciliata, Protozoa) und seine kompetitive Hemmung durch zweiwertige Kationen : Experimente mit der Voltage Clamp Methode

$\underline{Methods:}$ 1) The voltage-dependent inward current in Paramecium caudatum was studied under voltage clamp-conditions in the presence of Ca$^{++}$, Sr$^{++}$, Ba$^{++}$, M$^{++}$, Co$^{++}$, Mn$^{++}$ and Ni$^{++}$. 2) In contrast to the conventional technique the cells were impaled from above while they were observed from below. In this way straight electrodes could be used that are easier to pre pare than bent electrodes conventionally used. 3) The time required to set up a certain membrane potential could be reduced to 300$\mu$s by coating the electrode-tips and by shielding the sensor-electrode. 4) By depolarizing prepulses that inactivate the Ca$^{++}$-channel and by a subtraction-procedure the Ca$^{++}$- and K$^{+}$-currents duringexcitation could be separated (double pulse-technique). 5) In 'substitution-experiments' Ca$^{++}$ in the outer medium was exchanged by the tested cation. In 'addition-experiments' the Ca$^{++}$-concentration was kept constant while the tested cationwas added. [...