Journal article
Involvement of the Carboxy-Terminus Region of the Dihydropyridine Receptor β1a Subunit in Excitation-Contraction Coupling of Skeletal Muscle
Biophysical journal, Vol.77(6), pp.2953-2967
1999
DOI: 10.1016/S0006-3495(99)77128-6
Abstract
Skeletal muscle knockout cells lacking the
β subunit of the dihydropyridine receptor (DHPR) are devoid of slow L-type Ca
2+ current, charge movements, and excitation-contraction coupling, despite having a normal Ca
2+ storage capacity and Ca
2+ spark activity. In this study we identified a specific region of the missing
β1a subunit critical for the recovery of excitation-contraction. Experiments were performed in
β1-null myotubes expressing deletion mutants of the skeletal muscle-specific
β1a, the cardiac/brain-specific
β2a, or
β2a/
β1a chimeras. Immunostaining was used to determine that all
β constructs were expressed in these cells. We examined the Ca
2+ conductance, charge movements, and Ca
2+ transients measured by confocal fluo-3 fluorescence of transfected myotubes under whole-cell voltage-clamp. All constructs recovered an L-type Ca
2+ current with a density, voltage-dependence, and kinetics of activation similar to that recovered by full-length
β1a. In addition, all constructs except
β2a mutants recovered charge movements with a density similar to full-length
β1a. Thus, all
β constructs became integrated into a skeletal-type DHPR and, except for
β2a mutants, all restored functional DHPRs to the cell surface at a high density. The maximum amplitude of the Ca
2+ transient was not affected by separate deletions of the N-terminus of
β1a or the central linker region of
β1a connecting two highly conserved domains. Also, replacement of the N-terminus half of
β1a with that of
β2a had no effect. However, deletion of 35 residues of
β1a at the C-terminus produced a fivefold reduction in the maximum amplitude of the Ca
2+ transients. A similar observation was made by deletion of the C-terminus of a chimera in which the C-terminus half was from
β1a. The identified domain at the C-terminus of
β1a may be responsible for colocalization of DHPRs and ryanodine receptors (RyRs), or may be required for the signal that opens the RyRs during excitation-contraction coupling. This new role of DHPR
β in excitation-contraction coupling represents a cell-specific function that could not be predicted on the basis of functional expression studies in heterologous cells.
Details
- Title: Subtitle
- Involvement of the Carboxy-Terminus Region of the Dihydropyridine Receptor β1a Subunit in Excitation-Contraction Coupling of Skeletal Muscle
- Creators
- Maryline Beurg - Department of Physiology, University of Wisconsin School of Medicine, Madison, Wisconsin 53706, USAChris A Ahern - Department of Physiology, University of Wisconsin School of Medicine, Madison, Wisconsin 53706, USAPaola Vallejo - Department of Physiology, University of Wisconsin School of Medicine, Madison, Wisconsin 53706, USAMatthew W Conklin - Department of Physiology, University of Wisconsin School of Medicine, Madison, Wisconsin 53706, USAPatricia A Powers - Biotechnology Center, University of Wisconsin, Madison, Wisconsin 53706, USARonald G Gregg - Department of Biochemistry, University of Louisville, Louisville, Kentucky 40202 USARoberto Coronado - Department of Physiology, University of Wisconsin School of Medicine, Madison, Wisconsin 53706, USA
- Resource Type
- Journal article
- Publication Details
- Biophysical journal, Vol.77(6), pp.2953-2967
- Publisher
- Elsevier Inc
- DOI
- 10.1016/S0006-3495(99)77128-6
- ISSN
- 0006-3495
- eISSN
- 1542-0086
- Language
- English
- Date published
- 1999
- Academic Unit
- Molecular Physiology and Biophysics; Iowa Neuroscience Institute
- Record Identifier
- 9984070424602771
Metrics
14 Record Views