Effects of ionophore A23187 on ciliary activity of Paramecium caudatum

Abstract

The ciliated protozoan Paramecium caudatum (suspended in buffered solutions of pH 4.5–9.5) was treated with the ionophore A23187. With calcium and sodium as the only added extracellular cations, A23187 stopped ciliary motion and immobilized the cells. The rate of immobilization increased as a function of A23187 concentration (0.5–16 μg/mL) and extracellular calcium concentration (0.016–4 mM), but decreased as a function of increasing extracellular pH. The rate of immobilization was markedly sensitive to the extracellular calcium ion concentration at alkaline pH, but showed only slight calcium sensitivity at acid pH values. Continuous ciliary reversal (and thus backward swimming motion of the cells) was not observed under these conditions. However, extracellular magnesium ions (in a concentration-dependent manner) attenuated and even prevented the immobilization induced by calcium–A23187 treatment. In addition, in the presence of 1 mM Mg2+, a periodic ciliary reversal response was induced by calcium–A23187 treatment. At neutral pH values, the duration of this response increased as a function of extracellular calcium, but not magnesium, ion concentration. At neutral to alkaline pH values, a sustained slow backward swimming or circling motion (partial ciliary reversal) occurred after the period of periodic ciliary reversal.