SUMMARY The ciliated protozoan Paramecium spontaneously changes its swimming direction in the absence of external stimuli. Such behavior is based on resting potential fluctuations, the amplitudes of which reach a few mV. When the resting potential fluctuation is positive and large, a spike-like depolarization is frequently elicited that reverses the beating of the cilia associated with directional changes during swimming. We aimed to study how the resting potential fluctuation is amplified. Simultaneous measurements of the resting potential and intracellular Ca2+([Ca2+]i) from a deciliated cell showed that positive potential fluctuations were frequently accompanied by a small increase in[Ca2+]i. This result suggests that Ca2+influx through the somatic membrane occurs during the resting state. The mean amplitude of the resting potential fluctuation was largely decreased by either an intracellular injection of a calcium chelater (BAPTA) or by an extracellular addition of Ba2+. Hence, a small increase in[Ca2+]i amplifies the resting potential fluctuation. Simulation analysis of the potential fluctuation was made by assuming that Ca2+ and K+ channels of surface membrane are fluctuating between open and closed states. The simulated fluctuation increased to exhibit almost the same amplitude as the measured fluctuation using the assumption that a small Ca2+ influx activates Ca2+ channels in a positive feedback manner.

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Bull sperm and paramecium cilium were exposed to uniform static magnetic fields to observe their magnetic orientations and measure their anisotropic diamagnetic susceptibility (deltachi) for each. The prepared samples were whole bull sperm, bull sperm flat heads, and paramecium cilia, because bull sperm tails in a perfect condition could not be prepared. The whole bull sperm and the bull sperm heads became oriented perpendicular to the magnetic fields (1.7 Tesla maximum), while the paramecium cilia became parallel to the magnetic fields (8 Tesla maximum). A whole bull sperm, a bull sperm head, and a paramecium cilium were photometrically studied to obtain deltachi for each, which were estimated to be 1 x 10(-19), 3 x 10(-19), and 2 x 10(-20) J/T(2), respectively. deltachi of a sperm flagellum was estimated from the measured value of deltachi of the paramecium cilium, which agrees well with the difference between deltachi of the whole sperm and the sperm head. Additionally, this difference of deltachi almost coincides with the deltachi values calculated from deltachi of tubulin, as well. If the magnetic effect on biological systems is solved and the magnetic orientation correlates with it, deltachi will become the quantitative index of the effect.

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We found that a ciliated protozoan, Paramecium, swam perpendicular to a static (DC) magnetic field (0.68 T). The swimming orientation was similar even when the ionic current through the cell membrane disappeared after saponin treatment. To determine the diamagnetic anisotropy of intracellular organs, macronuclei, cilia, and secretory vesicles, trichocysts, were selectively isolated. Both cilia and trichocysts tended to align their long axis parallel to the magnetic field (0.78 T). Paramecium mutants that lack trichocysts also swam perpendicular to the magnetic field, although the proportion fraction was smaller than the normal population. Since large numbers of cilia and trichocysts are arranged at right angles to the long axis of the cell, the diamagnetic anisotropies of cilia and trichocysts cause the long axis of the cell to align perpendicular to the magnetic field. In contrast to the DC magnetic field, an alternative (AC) magnetic field (60 Hz, 0.65 T) had almost no effect on the swimming orientation of Paramecium.

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SYNOPSIS. The effect of temperature on the behavior of swimming cells of Paramecium caudatum has been investigated by photographic analyses of their tracks in uniform temperature, in temperature gradient, or in temperature changing with time. When the cells were placed in the temperature gradient, the frequency of discontinuous directional changes of cells swimming toward the optimal temperature, the temperature of the culture, was much lower than that of the cells swimming in the opposite direction. This difference in the frequency of directional changes explained the observed accumulation of the cells at ‐ the optimal temperature. When the temperature was suddenly changed toward the optimum, a transient decrease of the frequency of directional changes was observed and when the temperature was changed in the reverse direction, a transient increase of the frequency was noted. This transient response to the temperature change was the origin of the dependence of the frequency of directional changes on the swimming direction in the temperature gradient. Finally, the relation between the magnitude of the transient response and the rate of the temperature change was derived.

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