Measurements on permeabilized skeletal muscle fibers during continuous activation.

A mechanical stabilization technique involving the cycling of calcium activated rabbit psoas fibers between states of isometric force development and isovelocity shortenings at near maximal velocity (Vmax) was evaluated. This protocol succeeded in stabilizing both the sarcomere striation pattern and mechanical performance (isometric force and velocity of unloaded shortening) of the fibers for up to 10 min of continuous maximal calcium activation at 12 degrees C and for greater than 15 min at half-maximal activation. Between these cycling events, a variety of mechanical measurements can be made. A description of the strategies involved in the measurements and specific illustrations are presented. A general description of a computerized fiber mechanics system, which utilizes separate microprocessors for experimental control and data collection, is given. The techniques should be of general applicability to muscle physiologists studying permeabilized preparations and offer the great advantage of providing reproducibility of measurement in a stable preparation.