Studies upon the physio-chemical basis of behaviour in Tetrahmena

Brown, Ian Douglas (1989) Studies upon the physio-chemical basis of behaviour in Tetrahmena. University of Southampton, Doctoral Thesis.

Abstract

Twenty-eight chemicals were tested for their effect upon the swimming velocity of Tetrahymena vorax, including many neurotransmitters together with some of their agonists and antagonists. Acetylcholine produced a decrease in the forward swimming velocity, with a lower threshold concentration of 0.5 x 10^-8M. The effect of acetylcholine was enhanced by eserine and antagonized by d-tubocurarine, giving a decrease and increase in forward swimming velocity respectively. Our results suggest that acetylcholine is acting intracellularly and support evidence that it may be controlling the Ca⁺⁺ conductance across the excitable membrane. In electric fields of less than 200V Tetrahymena vorax exhibited a cathodal galvanotaxic response. The forward swimming velocity was inversely proportional to the external [K+]. The amplitude of the swimming wave was reduced in 8 mM K+ in electrical fields of both 3 and 40V. An initial decrease in forward swimming velocity in calcium concentrations between 0.125 and 0.25 mM was reversed at higher calcium concentrations reaching a plateau at 1mM in fields of both 3 and 40V. The amplitude of the swimming wave showed an inverse relationship to the swimming velocity at similar calcium concentrations. Procaine reduced the amplitude of the swimming wave at both 3 and 40V. The swimming velocity and the amplitude of the helical swimming path of T.pyriformis-NT1 cells grown at 20^oC (T_g 20^oC) and 38^oC (T_g 38^oC) were monitored between 0 and 40^oC in the presence and absence of electric fields. Within physiological limits the swimming velocity increased and the amplitude decreased as temperature was raised. The temperature profiles of these properties were not linear, and showed discontinuities at different temperatures for the different cultures. The break points in Arrhenius plots of the swimming velocity and swimming amplitude are tabulated and compared. The initial breakpoints upon cooling were clustered about the breakpoints in fluorescence polarization of D.P.H. in extracted phospholipids, and around the transition temperatures estimated from the literature for the pellicular membrane of these cells. The average of the initial breakpoints on cooling was 22.9^oC for T_g 38^oC cells and 13.7^oC for T_g 20^oC cells, a shift of 9.2^oC. Swimming velocity was correlated with membrane fluidity within physiological limits, but for other parameters the relationship with fluidity was more complex. While fluidity can affect the operation of membrane processes within physiological limits, its influence is less important than the maintenance of lipids in the liquid-crystalline state and their specific physical and chemical interactions with proteins. Cultures of T.pyriformis-NT1 were grown at 20^oC and 38^oC. G.L.C. analysis of fluorescence polarization measurements in extracted phospholipids indicated that there was increased saturation of fatty acids and relatively reduced fluidity as growth temperature was increased. Breakpoints occurred in the Arrhenius plots of fluorescence polarization at 16^oC for T_g 38^oC total extracted phospholipids and 9^oC for T_g 20^oC lipids.(DX88322)

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