Ca²⁺-induced tension development in the stalks of glycerinated Vorticella convallaria

We have developed a method of measuring the isometric tension in glycerinated stalks of Vorticella convallaria. Using this method, we measured tension vs. pCa relations in glycerinated V. convallaria stalks. The maximum isometric tension was 4 x 10^-8 N on average. The Hill's parameter, n, which is the number of calcium ions bound simultaneously and cooperatively to a contractile element (a force generating element), is approximately 3.2 when the Ca²⁺ concentration is increased and 2.5 when it is decreased. In order to estimate the efficiency of the energy conversion of Ca²⁺ binding to mechanical work, we measured the Ca²⁺-induced Carnot cycle in the Vorticella stalk. The energy efficiency was tentatively estimated to be about 7%. With this method, we have also succeeded in measuring the isometric tension of isolated spasmoneme, the rubber-like contractile fibrous organelle in the stalk. The maximum tension of spasmoneme was approximately one tenth that of the glycerinated stalk. We speculate that the isolated spasmoneme was only partially functional due to damage sustained when it was pulled out of the stalk.