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Journal of Experimental Biology, Vol 201, Issue 11 1835-1846, Copyright © 1998 by Company of Biologists

JOURNAL ARTICLES

Long-term adaptation of Ca2+-dependent behaviour in Paramecium tetraurelia

RR Preston and JA Hammond
Department of Physiology, M.C.P. Hahnemann School of Medicine, Allegheny University of the Health Sciences, 2900 Queen Lane, Philadelphia, PA 19129, USA. presoR@wpo.auhs.edu

Prolonged exposure to KCl has long been recognized to modify swimming behaviour in Paramecium tetraurelia, a phenomenon known as 'adaptation'. In this study, we have investigated behavioural adaptation systematically. A 24 h exposure to 30 mmol l-1 KCl deprived cells of the ability to respond behaviourally to two established chemoeffectors. We also explored the effects of 30 mmol l-1 KCl on the duration of backward swimming induced by Ba2+ and Mg2+. A brief (60 min) exposure prevented cells from swimming backwards in response to either cation, but recovery was rapid (<60 min) following a return to control medium. Prolonged (48 h) exposure caused a more persistent loss of response to Ba2+, so that several hours was now required for recovery. Surprisingly, responses to Mg2+ reappeared during 6-8 h in KCl, with backward swimming durations increasing to more than 300 % of control values after 26 h. Thus, we can distinguish two phases to adaptation. The short-term phase is characterized by an inability to respond behaviourally to most stimuli and might be adequately explained in terms of Ca2+ channel inactivation and K+-induced shifts in membrane potential. The long-term phase is characterized by enhanced responses to Mg2+ (and also to Na+), suggesting that a more extensive reprogramming of membrane excitability may occur during chronic K+-induced depolarization.


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