Last second twitch-response test of single intact skeletal muscle fibers prior to quick-freezing after various stimulation intervals

Abstract

Conventional chemical fixation of muscle fibers is not suited to disclose morphological changes occurring with a time course of only a few msec, e.g.during excitation-contraction-coupling. We have taken advantage of a quick-freeze method to be able to study single intact frog skeletal muscle fibers (r.temporaria) after various time intervals following electrical stimulation. The electronics were designed to permit any time interval from 0 to more than 1 sec between stimulation and impact of the specimen on a liquid He-cooled copper block. It is important to monitor the twitch-response to stimulation. Given the geometry of the freezing device ("Slammer", Polaron), and the fact that the device does not operate vibration-free, it is quite difficult to design and built an effective monitor able to record the actual twitch-response following the stimulation of an isolated single muscle fiber during its descent prior to freezing. We have built a simple device that allows visual observation of the twitch-response within a few seconds prior to the definitive stimulation during the specimen drop.