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Spontaneous All‐or‐Nothing Action Potentials in the Ciliate Bursaridium difficile
Author(s) -
BERG TROND OLAV,
SAND OLAV
Publication year - 1994
Publication title -
journal of eukaryotic microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.067
H-Index - 77
eISSN - 1550-7408
pISSN - 1066-5234
DOI - 10.1111/j.1550-7408.1994.tb05928.x
Subject(s) - ciliate , membrane potential , biology , capacitance , biophysics , physics , electrode , ecology , quantum mechanics
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 (MΩ) (n = 63) and 457 ± 150 picofarads (pF) (n = 42), respectively. Based on an estimated surface area of 6.8 × 10 ‐4 cm 2 , the corresponding specific membrane resistance and capacitance are 7.4 × 10 4 Ω× cm 2 and 0.7 μF/cm 2 . 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 displayed a prolonged plateau phase (0.5–1 s). The action potentials were abolished in nominal Ca 2+ ‐free solution and are thus Ca 2+ ‐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 Ca 2+ ‐free solution. The periods of backward swimming activity are thus linked to the spontaneous action potentials.