title: Rem uncouples excitation-contraction coupling in adult skeletal muscle fibers.
abstract: In skeletal muscle, excitation-contraction (EC) coupling requires depolarization-induced conformational rearrangements in L-type Ca(2+) channel (Ca(V)1.1) to be communicated to the type 1 ryanodine-sensitive Ca(2+) release channel (RYR1) of the sarcoplasmic reticulum (SR) via transient protein-protein interactions. Although the molecular mechanism that underlies conformational coupling between Ca(V)1.1 and RYR1 has been investigated intensely for more than 25 years, the question of whether such signaling occurs via a direct interaction between the principal, voltage-sensing α(1S) subunit of Ca(V)1.1 and RYR1 or through an intermediary protein persists. A substantial body of evidence supports the idea that the auxiliary β(1a) subunit of Ca(V)1.1 is a conduit for this intermolecular communication. However, a direct role for β(1a) has been difficult to test because β(1a) serves two other functions that are prerequisite for conformational coupling between Ca(V)1.1 and RYR1. Specifically, β(1a) promotes efficient membrane expression of Ca(V)1.1 and facilitates the tetradic ultrastructural arrangement of Ca(V)1.1 channels within plasma membrane-SR junctions. In this paper, we demonstrate that overexpression of the RGK protein Rem, an established β subunit-interacting protein, in adult mouse flexor digitorum brevis fibers markedly reduces voltage-induced myoplasmic Ca(2+) transients without greatly affecting Ca(V)1.1 targeting, intramembrane gating charge movement, or releasable SR Ca(2+) store content. In contrast, a β(1a)-binding-deficient Rem triple mutant (R200A/L227A/H229A) has little effect on myoplasmic Ca(2+) release in response to membrane depolarization. Thus, Rem effectively uncouples the voltage sensors of Ca(V)1.1 from RYR1-mediated SR Ca(2+) release via its ability to interact with β(1a). Our findings reveal Rem-expressing adult muscle as an experimental system that may prove useful in the definition of the precise role of the β(1a) subunit in skeletal-type EC coupling.
authors.affiliation: Department of Medicine-Cardiology Division, University of Colorado Denver-Anschutz Medical Campus, Aurora, CO 80045.
authors.forename: Donald
authors.initials: D
authors.lastname: Beqollari
authors.affiliation: Department of Medicine-Cardiology Division, University of Colorado Denver-Anschutz Medical Campus, Aurora, CO 80045.
authors.forename: Christin F
authors.initials: CF
authors.lastname: Romberg
authors.affiliation: Institute of Vegetative Physiology, University Hospital of Köln, D-50931 Köln, Germany.
authors.forename: Dilyana
authors.initials: D
authors.lastname: Filipova
authors.affiliation: Department of Medicine-Cardiology Division, University of Colorado Denver-Anschutz Medical Campus, Aurora, CO 80045 Departamento de Fisiología y Biofísica, Facultad de Medicina, Universidad Autónoma de San Luis Potosí, 78210 San Luis Potosí, Mexico.
authors.forename: Ulises
authors.initials: U
authors.lastname: Meza
authors.affiliation: Institute of Vegetative Physiology, University Hospital of Köln, D-50931 Köln, Germany.
authors.forename: Symeon
authors.initials: S
authors.lastname: Papadopoulos
authors.affiliation: Department of Medicine-Cardiology Division, University of Colorado Denver-Anschutz Medical Campus, Aurora, CO 80045 roger.bannnister@ucdenver.edu.
authors.forename: Roger A
authors.initials: RA
authors.lastname: Bannister
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000378:metabolism; D020013:Calcium Signaling / Q000502:physiology; D002462:Cell Membrane / Q000378:metabolism / Q000502:physiology; D056966:Excitation Contraction Coupling / Q000502:physiology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D020559:Monomeric GTP-Binding Proteins / Q000378:metabolism*; D009119:Muscle Contraction / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000378:metabolism* / Q000502:physiology; D011485:Protein Binding / Q000502:physiology; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism / Q000502:physiology
chemical_list: D020746:Calcium Channels, L-Type; C108135:Rem protein, mouse; D019837:Ryanodine Receptor Calcium Release Channel; C000592747:ryanodine receptor 1, mouse; D020559:Monomeric GTP-Binding Proteins; D002118:Calcium