Upadhyaya Lab
Biophysics of cellular movements


Measuring the contraction of a biological spring


Time series of Vorticella contraction (time shown in milliseconds). The scale bar is 35 microns. The initially straight stalk bends and coils into a helix, starting from the region near the cell body and moving down towards the base of the stalk with continuously changing helical pitch. The cell body moves without any observable rotation until the end of the contraction. After the stalk becomes fully coiled, the zooid starts rotating in a clockwise direction.


Vorticella convallaria is one of the fastest and most powerful biological springs. The cell body is attached to a substrate by a slender stalk containing a rod-like polymeric structure - the spasmoneme. Helical coiling of the stalk results from rapid contraction of the spasmoneme using a calcium dependent mechanism. Binding of calcium by the Ca-binding proteins called spasmins is believed to be the principal source for the contraction. In the absence of calcium, the spasmin filaments are negatively charged and in an extended state due to electrostatic repulsion. Calcium binding neutra lizes the charges and leads to an entropic collapse of the spasmoneme.We have conducted high-speed imaging experiments to study the contraction dynamics. These include measuring the contraction velocity and force as a function of increasing viscous load to obtain force-velocity curves. We have also used beads as markers on the stalk to obtain important information about the signal propagation mechanism that leads to contraction. We find that the spasmoneme behaves as a self-reinforcing spring and that the contraction starts at the cell body and proceeds down the stalk.