Rhythmic spontaneous depolarizations determine a slow-and-fast rhythm in walking of the marine hypotrich Euplotes vannus

Autor(en): Lueken, W
Ricci, N
Kruppel, T
Stichwörter: BEHAVIOR; behaviour; CALCIUM; calcium ions; CILIATE; Euplotes vannus; EXCITABILITY; MEMBRANE CURRENTS; Microbiology; speed rhythm; spontaneous depolarizations
Erscheinungsdatum: 1996
Volumen: 32
Ausgabe: 1
Startseite: 47
Seitenende: 54
In the marine hypotrich Euplotes vannus, the coupling of behavioural elements to shifts in the freely fluctuating membrane potential was investigated by use of a computerized locomotion track evaluation system. Potential shifts were attributed to bearing of cirri by single-image analysis of simultaneous video-tape recordings. Walking speed rhythmically decreases for 150-200 ms, and increases for 550-670 ms with a frequency of similar to 1.3/s. This pattern is caused by repetitive, spontaneous depolarizations of similar to 200 ms duration from about -25 mV to about -15 mV with a similar frequency. The speed is decreased by the combined reduction of the stroke amplitude of the fronto-ventral cirri and anteriad bending of the transverse cirri. Both the depolarizations and the walking pattern persist in a solution with a reduced Ca2- activity of 50 mu mol/l. Arhythmic spontaneous long depolarizations of 600-1200 ms duration induce a deceleration until movements stop and a fast backward jerking upon reversal of the beat direction of all cirri. This `'side-stepping'' (''avoiding'') reaction requires a high extracellular calcium concentration. Presumably, the depolarization rhythm is based on a pacemaking sequence of conductance changes of potassium.
ISSN: 09324739
DOI: 10.1016/S0932-4739(96)80038-1

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