Localization in the II-III loop of the dihydropyridine receptor of a sequence critical for excitation-contraction coupling.
Skeletal and cardiac muscles express distinct isoforms of the dihydropyridine receptor (DHPR), a type of voltage-gated Ca2+ channel that is important for excitation-contraction (EC) coupling. However, entry of Ca2+ through the channel is not required for skeletal muscle-type EC coupling. Previous work (Tanabe, T., Beam, K. G., Adams, B. A., Niidome, T., and Numa, S. (1990) Nature 346, 567-569) revealed that the loop between repeats II and III (II-III loop) is an important determinant of skeletal-type EC coupling. In the present study we have further dissected the regions of the II-III loop critical for skeletal-type EC coupling by expression of cDNA constructs in dysgenic myotubes. Because Ser687 of the skeletal II-III loop has been reported to be rapidly phosphorylated in vitro, we substituted this serine with alanine, the corresponding cardiac residue. This alanine-substituted skeletal DHPR retained the ability to mediate skeletal-type EC coupling. Weak skeletal-type EC coupling was produced by a chimeric DHPR, which was entirely cardiac except for a small amount of skeletal sequence (residues 725-742) in the II-III loop. Skeletal-type coupling was stronger when both residues 725-742 and adjacent residues were skeletal (e.g. a chimera containing skeletal residues 711-765). However, residues 725-742 appeared to be critical because skeletal-type coupling was not produced either by a chimera with skeletal residues 711-732 or by one with skeletal residues 734-765.
Nakai
J
J
Department of Information Physiology, National Institute for Physiological Sciences, Myodaiji-cho, Okazaki, 444-8585, Japan.
Tanabe
T
T
Konno
T
T
Adams
B
B
Beam
K G
KG
D000595:Amino Acid Sequence; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000737:chemistry / Q000378:metabolism*; D020746:Calcium Channels, L-Type; D002478:Cells, Cultured; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D008969:Molecular Sequence Data; D009119:Muscle Contraction; D009124:Muscle Proteins / Q000737:chemistry / Q000378:metabolism; D018482:Muscle, Skeletal / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D010766:Phosphorylation; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D009124:Muscle Proteins; D011993:Recombinant Fusion Proteins; D017868:Cyclic AMP-Dependent Protein Kinases; D002118:Calcium