Functional calcium release channel formed by the carboxyl-terminal portion of ryanodine receptor.
The ryanodine receptor (RyR) is one of the key proteins involved in excitation-contraction (E-C) coupling in skeletal muscle, where it functions as a Ca2+ release channel in the sarcoplasmic reticulum (SR) membrane. RyR consists of a single polypeptide of approximately 560 kDa normally arranged in a homotetrameric structure, which contains a carboxyl (C)-terminal transmembrane domain and a large amino (N)-terminal cytoplasmic domain. To test whether the carboxyl-terminal portion of RyR is sufficient to form a Ca2+ release channel, we expressed the full-length (RyR-wt) and C-terminal (RyR-C, approximately 130 kDa) RyR proteins in a Chinese hamster ovary (CHO) cell line, and measured their Ca2+ release channel functions in planar lipid bilayer membranes. The single-channel properties of RyR-wt were found to be similar to those of RyR from skeletal muscle SR. The RyR-C protein forms a cation-selective channel that shares some of the channel properties with RyR-wt, including activation by cytoplasmic Ca2+ and regulation by ryanodine. Unlike RyR-wt, which exhibits a linear current-voltage relationship and inactivates at millimolar Ca2+, the channels formed by RyR-C display significant inward rectification and fail to close at high cytoplasmic Ca2+. Our results show that the C-terminal portion of RyR contains structures sufficient to form a functional Ca2+ release channel, but the N-terminal portion of RyR also affects the ion-conduction and calcium-dependent regulation of the Ca2+ release channel.
Bhat
M B
MB
Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106, USA.
Zhao
J
J
Takeshima
H
H
Ma
J
J
D000818:Animals; D001483:Base Sequence; D016466:CHO Cells; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000096:biosynthesis / Q000737:chemistry* / Q000502:physiology*; D006224:Cricetinae; D004533:Egtazic Acid / Q000494:pharmacology; D004553:Electric Conductivity; D008564:Membrane Potentials / Q000187:drug effects; D008969:Molecular Sequence Data; D009119:Muscle Contraction; D009124:Muscle Proteins / Q000096:biosynthesis / Q000737:chemistry* / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D016254:Mutagenesis, Insertional; D010446:Peptide Fragments / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D011817:Rabbits; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism; D019837:Ryanodine Receptor Calcium Release Channel
D015220:Calcium Channels; D009124:Muscle Proteins; D010446:Peptide Fragments; D011994:Recombinant Proteins; D019837:Ryanodine Receptor Calcium Release Channel; D004533:Egtazic Acid; D002118:Calcium