Involvement of the Glu724–Pro760 Region of the Dihydropyridine Receptor II-III Loop in Skeletal Muscle-type Excitation-Contraction Coupling

Ca2+-dependent Dual Functions of Peptide C

“…Peptide C Shows Ca 2ϩ -dependent Dual Functions-As previously described (6,13), at a higher [Ca 2ϩ ] (e.g. at 1.0 M), peptide C produced no appreciable effect on the RyR, but if present together with peptide A, peptide C inhibited peptide A-induced activation of the RyR (i.e.…”

“…In our previous studies (6,11,13,14), we reported that peptide A enhances ryanodine binding and induces a rapid Ca 2ϩ release, whereas peptide C antagonizes the activation of ryanodine binding and Ca 2ϩ release by peptide A. However, most of our previous studies were carried out at [Ca 2ϩ ]s higher than 0.2 M; many experiments were carried out at or higher than 1.0 M. Because the in vivo studies of E-C coupling described in the Introduction (3,4,16) Concentration Ranges in an RyR1-specific Manner- Fig.…”

“…11) region or in the Thr 671 -Glu 680 region (12) has not yet been settled. Another peptide corresponding to the Glu 724 -Pro 760 region of the II-III loop, peptide C, inhibited peptide A-mediated activation of the RyR (6,13,14) and also produced a small inhibition of depolarization-induced tension development in the skinned muscle fiber (15). Thus, the information derived from the peptide probe studies suggested that these two regions of the II-III loop are involved in E-C coupling (13).…”

“…Can we find any of the functions required for E-C coupling, such as activation, re-priming, and physical linking of the II-III loop with the RyR? As described previously (6,(13)(14)(15), peptide C that corresponds to essentially the same region as the Leu 720 -Leu 764 region suppresses activation of the RyR by peptide A and T-tubule depolarization, suggesting that this region may be required for at least the blocking or re-priming process of E-C coupling. According to the recent report by Stange et al (12), the peptide * This work was supported by National Institutes of Health Grant AR 16922.…”

“…The time course of Ca 2ϩ release was monitored in a stopped-flow apparatus (Bio-Logic SFM-4 with a MOS-200 optical system; excitation at 440 nm, emission at 510 nm using an interference filter with 40 nm of bandwidth) using fluo-3 as a Ca 2ϩ indicator as described previously (13,22,23). Six to ten traces (each representing 1,000 data points) of the fluo-3 signal were averaged for each experiment.…”