Effects on ca2+-activated tension due to a synthetic n-terminal
actin peptide in single skeletal muscle fibers.
Metzger, Joseph M.
Department of Physiology, University of Michigan School of
Medicine, Ann Arbor, MI 48109.
APStracts 2:0184C, 1995.
Insight into the mechanism of force development in striated muscle
will be provided by elucidating the specific regions of the actin
molecule which interact with myosin and regulatory subunits of the
thin filament during Ca2+-activated contraction. There is growing
evidence that the acidic N-terminal domain of actin may 1) represent
an important binding site for myosin, and 2) interact with the
inhibitory region of troponin I. The purpose of this study was to
determine the effects of a synthetic peptide corresponding to a
specific sequence of the N-terminal domain of skeletal muscle actin
on Ca2+-activated tension in chemically skinned single psoas skeletal
muscle fibers. This study focused on the highly conserved Lys18-Arg28
amino acid sequence of actin, a region of native actin that is
thought to interact with both troponin I and myosin. The effects of
synthetic actin peptide Lys18-Arg28 on tension development were shown
to vary depending on 1) the concentration of Ca2+ present in the
activating solutions, and 2) the peptide concentration. At submaximal
concentrations of Ca2+, isometric tension was reversibly potentiated
in the presence of 100-500 _M synthetic actin peptide Lys18-Arg28.
Importantly, scrambling the sequence of Lys18-Arg28 fully abolished
the increase in Ca2+ sensitivity, providing evidence that the
observed effects were specific to the sequence of peptide Lys18
-Arg28. In contrast, maximum Ca2+-activated tension was inhibited by
mM concentrations of both Lys18-Arg28 and the scrambled peptide,
indicating that this effect was non-specific. The effect of peptide
Lys18-Arg28 to increase the Ca2+ sensitivity of tension is not known
but may be due to an effect of the actin peptide to alter thin
filament activation, a possibility consistent with proposed
interactions between this domain of actin and the inhibitory region
of troponin I.
Received 21 November 1994; accepted in final form 25 April 1995
APS Manuscript Number C683-4.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 9 May 1995.