Summary
The amount of Ca++ which is bound to the surface of Paramecium can be controlled by the relative concentrations of cations, and determines, in part, the ciliary response to cationic stimuli (Naitoh and Yasumasu, 1967; Naitoh, 1968). Experiments were performed to examine the relationship between cationic concentration and binding on the one hand, and electrical behavior of the cell on the other. Solutions of Ca++, and solutions of calcium plus Mg++, Ba++, K+, Na+ or Rb+were tested at concentrations of 0.06 to 16 mM. In calcium solutions the I-V characteristics were relatively independent of [Ca], while the resting potential dropped with a slope of 20 mV per decade increase in [Ca]. In mixtures of Ca plus other cations I-V characteristics were also relatively independent of ionic concentrations, provided the amount of bound calcium was held constant. The slope resistance in the region of zero current was also dependent on bound calcium, but was somewhat complicated by specific properties of some cationic species. All the cations tested lowered the resting potential, and hence the membrane appears to have poor cation permselectivity. Cationic permeability was largely a function of the degree of saturation of the anionic binding sites with Ca++; with a decrease in bound Ca the conductance to any cation was increased.
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On leave of absence from the Zoological Institute, Faculty of Science, University of Tokyo.
We gratefully acknowledge the kind help of Dr. H. Grundfest in criticizing the manuscript, and in offering instructive suggestions.
Support came from National Science Foundation grant GB-5752X, U.S.P.H.S. grant NB-03664, and in part from Office of Naval Research grant Nonr 4785(00) administered by the Marine Biological Laboratory.
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Naitoh, Y., Eckert, R. Electrical properties of Paramecium caudatum: modification by bound and free cations. Z. Vergl. Physiol. 61, 427–452 (1968). https://doi.org/10.1007/BF00297875
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DOI: https://doi.org/10.1007/BF00297875