Control of Ciliary Activity in <I>Paramecium</I> by Intracellular Injec- tion of Calcium Buffers

Abstract

Mixtures of calcium and EGTA [ethyleneglycol bis (β-amino- ethylether)-N, N'-tetraacetate] solution containing stabilized concentrations ofionized calcium (calcium buffers) were injected into ciliate Paramecium caudatum. Ciliary reversal was induced when the ionized calcium concentra- tion in the buffer was above a certain level. The threshold Ca2+ concentration for inducing ciliary reversal varied (10-6-10-8 M) by the pH of the buffer and by the medium surrounding the organism. From theoretical considerations and the experimental results, it was concluded that the threshold difference in Ca2+ concentration was due to insufficient pH-buffering action of the injected liquid and to differences in pH values in the protoplasm of the organism in different media. This conclusion is consistent with the result of the Triton-extracted model in which the threshold concentration of calcium ions for inducing ciliary reversal was 10-6 M. Injection of potassium citrate solution into the organism induced ciliary reversal. The implications of the latter result are discussed.