Long-term adaptation of Ca2+-dependent behaviour in Paramecium tetraurelia.
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.
Preston
R R
RR
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
Hammond
J A
JA
D000222:Adaptation, Physiological; D000818:Animals; D001464:Barium / Q000494:pharmacology; D001522:Behavior, Animal / Q000187:drug effects*; D002118:Calcium / Q000494:pharmacology*; D015220:Calcium Channels / Q000502:physiology; D002628:Chemoreceptor Cells / Q000502:physiology; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D010247:Paramecium / Q000502:physiology*; D011189:Potassium Chloride / Q000008:administration & dosage / Q000494:pharmacology; D013550:Swimming
D015220:Calcium Channels; D001464:Barium; D011189:Potassium Chloride; D008274:Magnesium; D002118:Calcium