AJP - Cell Physiology, Vol 258, Issue 4 C618-C621, Copyright © 1990 by American Physiological Society
Contractions of frog tonus fibers and their modification by length changes
E. Bozler
Department of Physiology, Ohio State University, Columbus 43210.
Isometric and isotonic contractions of the tonus fibers of the frog were
recorded using anodal block of the nerve fibers of the twitch fibers.
Repetitive stimulation produced a contraction with a very slow rising phase
because the individual responses were very weak. The first two or three
stimuli usually did not give a visible response at all. However, if the
twitch fibers were also stimulated, the responses of the tonus fibers were
many times stronger and faster, but only under isotonic conditions. This
indicates that the large increase in the responses of the tonus fibers was
produced by the passive shortening caused by the contraction of the twitch
fibers. A strong and fast response of the tonus fibers was also obtained if
during stimulation of the tonus fibers the muscle was made to shorten by
diminishing the load. It is suggested that the enormous effect of
shortening is due to the regenerating action of shortening previously
demonstrated.
