Thermo-sensitive response based on the membrane fluidity adaptation inParamecium multimicronucleatum

Abstract

SUMMARYRelationships between the thermo-sensitive response and membrane lipid fluidity were studied using a ciliated protozoan, Paramecium multimicronucleatum. Paramecium elicits a transient membrane depolarization in response to a cooling stimulus (temperature drop). The depolarization amplitude was largest when the cooling stimulus was started from the culture temperature, whilst when cooling started at a temperature more than 5°C higher or lower than the culture temperature, only a small depolarization was induced. Therefore, the cooling-induced response was dependent on the culture temperature and its sensitivity to the cooling stimulus was highest at the culture temperature. Membrane fluidity measurements of living cells using the fluorescent dye 6-lauroyl-2-dimethylaminonaphthalene (laurdan) showed that the fluidity measured at the culture temperature was almost constant irrespective of the temperature at which the cells had been cultured and adapted, which is consistent with homeoviscous adaptation. The constant fluidity at the culture temperature quickly decreased within a few seconds of application of the cooling stimulus, and the decreased fluidity gradually readapted to a constant level at the decreased temperature within 1 h. When the constant fluidity at culture temperature was modified by the addition of procaine or benzyl alcohol, the cooling-induced depolarization was completely abolished. These results suggest the possibility that the adaptation of fluidity to a constant level and its quick decrease below the constant level activate cooling-sensitive channels to elicit the transient depolarization.

Orientation of paramecium swimming in a static magnetic field: Dependence on membrane lipid fluidity

“…In Paramecium, when the culture temperature is increased, the membrane fluidity increased at first, and then gradually dropped to a constant level during adaptation to the high temperature [Toyoda et al, 2009]. Inversely, when the culture temperature is decreased, the membrane fluidity decreased at first, then gradually rose to a constant level at the adapted temperature.…”

“…Inversely, when the culture temperature is decreased, the membrane fluidity decreased at first, then gradually rose to a constant level at the adapted temperature. These changes in the membrane fluidity were complete within 1-2 h. Therefore, when comparing the membrane fluidity at an intermediate temperature, the fluidity of cells cultured at a high temperature is lower than that of cells cultured at a low temperature [Toyoda et al, 2009]. Based on these results, selected syngens at the stationary phase were cultured for 1-3 days at 15, 25, or 35 8C, and their magnetic orientations were tested at 25 8C (Fig.…”

“…The GP distribution was obtained from histograms of GP images of the anterior part of each cell. The GP value was adopted from the mean of the GP distribution as in a previous report [Toyoda et al, 2009].…”

“…Since the membrane lipid fluidity of Paramecium is altered by the environmental temperature [Sasaki et al, 2006;Toyoda et al, 2009], the magnetic orientation of the cells in the rectangular vessel was tested at various temperatures. For all syngens tested, a rise in the vessel's temperature decreased the proportion of cells swimming perpendicular to the magnetic field (Fig.…”

Pharmacological investigation of the bioluminescence signaling pathway of the dinoflagellate Lingulodinium polyedrum: evidence for the role of stretch‐activated ion channels

“…Gd 3+ but not nifedipine inhibits benzyl alcohol activation of bioluminescence. To further explore the effect of membrane fluidity on stretch-sensitive channels, cells were treated with benzyl alcohol, a widely used membrane fluidizer at concentrations of 7-30 mM to increase membrane fluidity (Gordon et al 1980, Blixt et al 1993, Haidekker et al 2000, Balogh et al 2005, Toyoda et al 2009, Zhang et al 2011) and results in G protein activation (Gudi et al 1998, Chachisvilis et al 2006.…”