19-Residue Peptide from C-Terminal Tail of DHPR β1A Subunit Potentiates Voltage-Dependent Calcium Release in Adult Skeletal Muscle Fibers

Abstract

The skeletal muscle isoforms of the membrane-spanning α1s subunit and the cytoplasmic β1a subunit are essential during EC coupling. Recent evidence suggests that the activating effect of the full-length β1a subunit on isolated ryanodine receptor (RyR1) Ca2+ channels in lipid bilayer can be reproduced by a peptide (β1a 490-524) corresponding to the 35-residue C-terminal tail of the β1a subunit and also confirmed a high-affinity interaction between the C-terminal tail of the β1a and RyR1. We now tested the hypothesis that a 19 amino acid residue peptide (β1a 490-508) may be sufficient to reproduce activating effects already observed for β1a 490-524 as well as that of the full-length peptide. The hypothesis is based on existing results using overlapping peptides tested on isolated RyR1 in phospholipid bilayer (1). Here we examined the effects of β1a 490-508 on Ca2+ release during whole cell voltage-clamp depolarization of adult mouse FDB muscle fibers. 25 nM or 100 nM of β1a 490-508 peptide in a patch pipette caused a 25% increment in the SR Ca2+ release flux in single voltage clamped muscle fibers but with no significant shift in the voltage dependence of the maximum peak Ca2+ release flux. Considerably less activating effect was observed using 400 nM peptide. A scrambled form of the 19-residue peptide (100nM) was used as a negative control for the wild-type peptide and produced a negligible effect on the peak amplitude of Ca2+ release flux. Taken together, we have shown that the β1a 490-508 peptide contains molecular components sufficient to modulate EC coupling between DHPR and RyR1 in adult functioning muscle fibers. Supported by R01-AR055099 and T32-AR007592.1. Rebbeck, R.T. et. al. March (2011) Biophysical Society Abstract 3195-Pos/B300.