2+
T. Ikemoto et al
Dantrolene derivatives and Ca release
735
release (Hui, 1983; Shoshan-Barmatz et al., 1991; Partridge &
Valenzuela, 1999; Seutin et al., 2000). However, the exact
mechanism of action of Dan has remained unclear, not only
in skeletal muscles, but also in other types of cells. For
example, it is not clear whether the inhibitory action of Dan
on Ca2+ release results from direct binding to the RyR
(Parness & Palnitkar, 1995; Palnitkar et al., 1997; Fruen et
al., 1997). Therefore, it is important to elucidate the
molecular mechanism of Dan-induced inhibition of the
Ca2+ release via the RyR.
Some of the Dan derivatives we synthesized inhibited PCR
without an inhibitory eect on CICR. They inhibited Clof-
induced Ca2+ release in skinned ®bres, an eect that was
signi®cantly correlated with their inhibitory eect on twitch
tension (Figure 6c). In addition, GIF-0185 diminished the
inhibition by Dan on CICR, although it showed no
inhibitory eect on CICR (Figures 2b and 3a). These results
indicate that the target(s) of Dan and its derivatives are
clearly retained in skinned ®bres. Among these speci®c PCR
inhibitors at room temperature (21 ± 238C), GIF-0082, with
its azido-functionalized and iodinated structure, is applicable
to photo-anity and its binding experiment on target
molecule(s). Since GIF-0082 does not interfere with the
inhibitory action of Dan on CICR (unlike GIF-0185), it
might well be more speci®c to PCR than GIF-0185. We,
therefore, think that this agent may be a useful probe to
study PCR of skeletal muscles in various preparations
including isolated SR membranes and the puri®ed RyR.
We wish to thank Dr M. Iino (University of Tokyo, Japan) for
reading the manuscript. This work was supported by a Grant-in-
Aid from the Ministry of Education, Science, Sports, and Culture
of Japan.
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British Journal of Pharmacology vol 134 (4)