Direct measurement of Vorticella contraction force by micropipette deflection
Danielle C. France, Jonathan Tejada, Paul Matsudaira
The ciliated protozoan Vorticella convallaria is noted for its exceptionally fast ATP-independent cellular contraction, but direct measurements of contractile force have proven difficult given the length scale, speed, and forces involved. We used high speed video microscopy to image live Vorticella stalled in mid-contraction by deflection of an attached micropipette. Stall forces correlate with both distance contracted and the resting stalk length. Estimated isometric forces range from 95 177 nanonewtons (nN), or 1.12 nN per micrometer of the stalk. Maximum velocity and work are also proportional to distance contracted. These parameters constrain proposed biochemical/physical models of the contractile mechanism.