Acceleration of Paramecium Swimming Velocity is Effected by Various Cations

Acceleration of swimming velocity was induced by the transfer of Paramecium cells to solutions containing various multivalent cations, Fe3+, Ca2+, Mg2+, Tris+, and others. The monovalent cations, K+, Rb+, Li+ and Na+, however, suppressed the acceleration induced by the multivalent cations. Effects of Ca2+ and K+ on swimming velocity were antagonistic, as the Ca2+ concentration increased the K+ concentration acted to suppress the Ca2+ induced acceleration. As both the Ca2+ and K+ concentrations were low, this antagonistic relation could be represented by the concentration ratio, [K+]/[Ca2+]1/2. Acceleration of the swimming velocity took place when cells were transferred to a solution with a lower concentration ratio than that of the adapting solution used. Time courses of decreasing velocity after acceleration were examined at various concentrations of Ca2+ and K+, and for various temperatures. Change in membrane potential as measured with a microelectrode, was not consistently related to the change in swimming velocity. These results are discussed in relation to the driving force for the influx of Ca2+.