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Summary: Proc. Natl. Acad. Sci. USA
Vol. 96, pp. 58265831, May 1999
Physiology
Trading force for speed: Why superfast crossbridge kinetics leads
to superlow forces
LAWRENCE C. ROME*, CHRIS COOK§, DOUGLAS A. SYME*, MARTIN A. CONNAUGHTON*, MIRIAM ASHLEY-ROSS*,
ANDREI KLIMOV*, BORIS TIKUNOV*, AND YALE E. GOLDMAN§
*Biology Department, Leidy Laboratories, University of Pennsylvania, Philadelphia, PA 19104; §Department of Physiology, Pennsylvania Muscle Institute,
University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6083; and Marine Biological Laboratories, Woods Hole, MA 02543
Communicated by Clara Franzini-Armstrong, University of Pennsylvania School of Medicine, Philadelphia, PA, March 16, 1999 (received for review
January 25, 1999)
ABSTRACT Superfast muscles power high-frequency mo-
tions such as sound production and visual tracking. As a class,
these muscles also generate low forces. Using the toadfish
swimbladder muscle, the fastest known vertebrate muscle, we
examined the crossbridge kinetic rates responsible for high
contraction rates and how these might affect force generation.
Swimbladder fibers have evolved a 10-fold faster crossbridge
detachment rate than fast-twitch locomotory fibers, but sur-
prisingly the crossbridge attachment rate has remained un-
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