Rr. Preston et Ja. Hammond, LONG-TERM ADAPTATION OF CA2-DEPENDENT BEHAVIOR IN PARAMECIUM-TETRAURELIA(), Journal of Experimental Biology, 201(11), 1998, pp. 1835-1846
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 systemat
ically, A 24 h exposure to 30 mmol l(-1) KCl deprived cells of the abi
lity to respond behaviourally to two established chemoeffectors. We al
so explored the effects of 30 mmol l(-1) KCl on the duration of backwa
rd swimming induced by Ba2+ and Mg2+. A brief (60 min) exposure preven
ted cells from swimming backwards in response to either cation, but re
covery was rapid (<60 min) following a return to control medium. Prolo
nged (48 h) exposure caused a more persistent loss of response to Ba2, so that several hours was now required for recovery. Surprisingly, r
esponses to Mg2+ reappeared during 6-8 h in KCl, with backward swimmin
g durations increasing to more than 300 % of control values after 26 h
. Thus, we can distinguish two phases to adaptation. The short-term ph
ase is characterized by an inability to respond behaviourally to most
stimuli and might be adequately explained in terms of Ca2+ channel ina
ctivation and K+-induced shifts in membrane potential. The long-term p
hase is characterized by enhanced responses to Mg2+ (and also to Na+),
suggesting that a more extensive reprogramming of membrane excitabili
ty may occur during chronic Kf-induced depolarization.