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-actinin and dystrophin
Department of Physiology and Neurobiology, University of Connecticut, Storrs, Connecticut 06269
The
actin-binding proteins dystrophin and
-actinin are members of a
family of actin-binding proteins that may link the cytoskeleton to
membrane proteins such as ion channels. Previous work demonstrated that
the activity of Ca2+ channels can be regulated by agents
that disrupt or stabilize the cytoskeleton. In the present study, we
employed immunohistochemical and electrophysiological techniques to
investigate the potential regulation of cardiac L-type Ca2+
channel activity by dystrophin and
-actinin in cardiac myocytes and
in heterologous cells. Both actin-binding proteins were found to
colocalize with the Ca2+ channel in mouse cardiac myocytes
and to modulate channel function. Inactivation of the Ca2+
channel in cardiac myocytes from mice lacking dystrophin
(mdx mice) was reduced compared with that in wild-type
myocytes, voltage dependence of activation was shifted by 5 mV to more
positive potentials, and stimulation by the
-adrenergic pathway and
the dihydropyridine agonist BAY K 8644 was increased. Furthermore, heterologous coexpression of the Ca2+ channel with muscle,
but not nonmuscle, forms of
-actinin was also found to reduce
inactivation. As might be predicted from a reduction of
Ca2+ channel inactivation, a prolonging of the mouse
electrocardiogram QT was observed in mdx mice. These results
suggest a combined role for dystrophin and
-actinin in regulating
the activity of the cardiac L-type Ca2+ channel and a
potential mechanism for cardiac dysfunction in Duchenne and Becker
muscular dystrophies.
muscular dystrophy; intracellular regulation
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