Improved preparation and swimming behavior of Triton-extracted models of Didinium nasutum

An improved method for the preparation of Triton X-100 extracted models of Didinium nasutum was established. Didinium models prepared by treatment with a Triton X-100 solution, containing specific proteolysis inhibitors and dimethyl sulfoxide, maintained an intact shape at 25 degrees C for a longer time than models prepared by treatment with a Triton X-100 solution not containing the proteolysis inhibitors and dimethyl sulfoxide. The improved Didinium models were reactivated so as to swim forward in the presence of Mg2+ and ATP or ADP. They did not swim backward in response to Ca2+, in contrast to well-known Paramecium models. However, the improved Didinium models showed circular swimming and spinning in response to 10(-6) M or higher concentrations of Ca2+. This observation suggests that the quick directional change as well as the spinning, which are characteristic of live Didinium, are due to an increase in the endoplasmic Ca2+ concentration around the ciliary system. The response of the Didinium ciliary system to Ca2+ may differ from the response of the Paramecium ciliary system to Ca2+.