Meeting Abstract
Muscle intrinsically produces different amounts of force depending on its length and its velocity. These force-length and force-velocity relationships are often discussed when developing models of muscle function. My research examines a previously unsteady force-length relationship: how length affects the speed at which force develops. I measured a standard force-length curve in isolated muscle preparations from the silver lamprey, starting at the ascending limb, proceeding through optimal length, and down the descending limb to the point where peak muscle force was negligible. At each length, I stimulated the muscle to produce a twitch. From each of the twitches, the force produced by the muscle and the timing of various points relative to the stimulus was measured. During force development, the timing and force were measured at 50%, 90% and 100% maximal force. During force decay, the force and timing were measured at 50% and 90% relaxation. From these data, the rate of force development and decay was calculated at different portions of the twitch. Previous results show that on the ascending limb and the plateau region that the rate of force development increases as length increases and the rate muscle relaxation decreases with as length increases. We are currently extending these measurements onto the descending limb of the force-length curve, to determine whether this effect is due to myosin-actin overlap or some other biochemical effect such as titin winding. We hypothesize that if the changes in twitch kinetics are due to myosin-actin overlap, which increases on the ascending limb, then the rate of force development and the rate of muscle relaxation will decrease on the descending limb of the length tension curve as there is less and less myosin-actin overlap.
