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Biophys J, September 2001, p. 1419-1429, Vol. 81, No. 3
Departments of Biochemistry and Biophysics and Cell and Molecular Physiology, University of North Carolina, Chapel Hill, North Carolina 27599-7260 USA
The II-III cytoplasmic loop of the skeletal muscle
dihydropyridine receptor (DHPR) 
1-subunit is essential
for skeletal-type excitation-contraction coupling. Single channel and
[3H]ryanodine binding studies with a full-length
recombinant peptide (p666-791) confirmed that this region
specifically activates skeletal muscle Ca2+ release
channels (CRCs). However, attempts to identify shorter domains of the
II-III loop specific for skeletal CRC activation have yielded
contradictory results. We assessed the specificity of the interaction
of five truncated II-III loop peptides by comparing their effects on
skeletal and cardiac CRCs in lipid bilayer experiments; p671-680 and p720-765 specifically activated
the submaximally Ca2+-activated skeletal CRC in experiments
using both mono and divalent ions as current carriers. A third peptide,
p671-690, showed a bimodal activation/inactivation
behavior indicating a high-affinity activating and low-affinity
inactivating binding site. Two other peptides (p681-690
and p681-685) that contained an RKRRK-motif and have
previously been suggested in in vitro studies to be important for
skeletal-type E-C coupling, failed to specifically stimulate skeletal
CRCs. Noteworthy, p671-690, p681-690, and
p681-685 induced similar subconductances and long-lasting
channel closings in skeletal and cardiac CRCs, indicating that these
peptides interact in an isoform-independent manner with the CRCs.
Biophys J, September 2001, p. 1419-1429, Vol. 81, No. 3
© 2001 by the Biophysical Society 0006-3495/01/09/1419/11 $2.00
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