Gtp[delta]s removal of d600 block of skeletal muscle excitation
-contraction coupling.
Carney-Anderson, Lisa, Ladora V. Thompson, Daniel A. Huetteman, and
Sue K. Donaldson.
University of Minnesota, Department of Physiology and Department of
Physical Medicine and Rehabilitation, School of Medicine, and School
of Nursing, Minneapolis, Minnesota 55455
APStracts 3:0181G, 1996.
G proteins interacting with dihydropyridine receptors (DHPR) in
transverse tubules (TT) of skeletal muscle may have a role in
skeletal excitation-contraction (EC) coupling. The aim of this study
was to determine the effects of G protein-specific nucleotides
(GTP[delta]S, GDP[beta]S) on the EC coupling mechanism in the
presence of D600, an agent which blocks EC coupling by immobilizing
the voltage-sensing subunit of the DHPR in its inactivated state.
Using the mechanically peeled single fiber preparation from rabbit
adductor magnus skeletal muscle, 50[mu]M GTP[delta]S and 500[mu]M
GDP[beta]S were applied with the fiber in a D600-induced state of
blocked EC coupling. Neither nucleotide served as an independent
stimulus for sarcoplasmic reticulum (SR) Ca2+ release when added to
the TT polarizing bath under conditions of D600 block. The presence
of GTP[delta]S or GDP[beta]S during a complete EC coupling cycle
removed the D600 block of EC coupling despite continuous bath D600.
After the nucleotides were washed out, in the continued presence of
D600, the D600 block of EC coupling was reestablished. In contrast,
GTP[delta]S added only during the period of TT depolarization under
D600 block did not remove the D600 block of EC coupling even though
GTP[delta]S did stimulate SR Ca2+ release. GTP[delta]S had no effect
on submaximum (0.5-1.0mM) caffeine contractures and thus is unlikely
to be acting through the Ca2+-induced Ca2+ release mechanism of the
SR. These data suggest that the molecular binding site for
GTP[delta]S and GDP[beta]S is likely to be in the TT near the DHPR,
perhaps on a G protein.
Received 10 May 1993; accepted in final form 12 September 1996.
APS Manuscript Number G210-3.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 7 October 1996