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Department of Physiology, Emory University School of Medicine, Atlanta, Georgia 30322
The transverse tubules are highly specialized
invaginations of the cardiac sarcolemmal membrane involved in
excitation-contraction (EC) coupling. Several proteins directly
involved in EC coupling have been shown to reside either in the
transverse tubular membrane or in closely associated structures. With
the use of immunofluorescence microscopy, we have found that
GS and adenylyl cyclase, key
elements in the
-adrenergic signal transduction cascade, are
essentially homogeneously distributed throughout the transverse tubular
network of isolated rat ventricular myocytes.
GS, in particular, was much more
abundant within the transverse tubular membrane than in the peripheral
sarcolemma. Furthermore, both proteins are also present in the
intercalated disk region. The location of these elements of the
cAMP-signaling cascade within a few micrometers of every inotropic
target suggests that control and action of this second messenger are
quite local. Furthermore, a similar distribution is likely for
negatively inotropic receptor systems that oppose GS-linked receptors at the level
of adenylyl cyclase. Thus, in addition to their role in EC coupling,
transverse tubules appear to be the primary site for signaling by
inotropic agents.
signal transduction; immunolocalization
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