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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Ref ID : 7303

Trond Olav Berg and Olav Sand; Spontaneous All-or-Nothing Action Potentials in the Ciliate Bursaridium difficile. J.Eukaryot.Microbiol. 41(1):13-17, 1994

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The electrical membrane properties and the swimming behaviour of the freshwater ciliate Bursaridium difficile were studied by current clamp recordings and video analysis. The resting membrane potential was- 45+/-6 mV (mean+/-SD, n=80), and the input resistance and membrane capacitance were 109+/-42 megaohms (n=63) and 457+/-150 picofarads (pF) (n=42), respectively. Based on an estimated surface area of 6.8x10E-4 cm2, the corresponding specific membrane resistance and capacitance are 7.4x10E4 ohms x cm2 and 0.7 µF/cm2. Bursaridium difficile generates spontaneous, all-or-nothing action potentials with a well-defined threshold in normal medium. The spontaneous firing frequency was 0.22+/-0.06 Hz (n=80). The maximum rate of rise of the action potentials was less than 1 V/s, and they displaced a prolonged plateau phase (0.5-1 sec). The action potentials were abolished in nominal Ca2+ -free solution and are thus Ca2+ -spikes. The swimming pattern of Bursaridium in homogeneous surroundings is composed of forward swimming periods interrupted by regular, short periods of backward swimming followed by a change in the forward swimming direction. The turning frequency corresponded to the spontaneous firing frequency, and only forward swimming was observed in nominal Ca2+ -free solution. The periods of backward swimming activity are thus linked to the spontaneous action potentials.