β1a490–508, a 19-Residue Peptide from C-Terminal Tail of Cav1.1 β1a Subunit, Potentiates Voltage-Dependent Calcium Release in Adult Skeletal Muscle Fibers

Abstract

The α1 and β1a subunits of the skeletal muscle calcium channel, Cav1.1, as well as the Ca2+ release channel, ryanodine receptor (RyR1), are essential for excitation-contraction coupling. RyR1 channel activity is modulated by the β1a subunit and this effect can be mimicked by a peptide (β1a490–524) corresponding to the 35-residue C-terminal tail of the β1a subunit. Protein-protein interaction assays confirmed a high-affinity interaction between the C-terminal tail of the β1a and RyR1. Based on previous results using overlapping peptides tested on isolated RyR1, we hypothesized that a 19-amino-acid residue peptide (β1a490–508) is sufficient to reproduce activating effects of β1a490–524. Here we examined the effects of β1a490–508 on Ca2+ release and Ca2+ currents in adult skeletal muscle fibers subjected to voltage-clamp and on RyR1 channel activity after incorporating sarcoplasmic reticulum vesicles into lipid bilayers. β1a490–508 (25 nM) increased the peak Ca2+ release flux by 49% in muscle fibers. Considerably fewer activating effects were observed using 6.25, 100, and 400 nM of β1a490–508 in fibers. β1a490–508 also increased RyR1 channel activity in bilayers and Cav1.1 currents in fibers. A scrambled form of β1a490–508 peptide was used as negative control and produced negligible effects on Ca2+ release flux and RyR1 activity. Our results show that the β1a490–508 peptide contains molecular components sufficient to modulate excitation-contraction coupling in adult muscle fibers.