ZFIN ID: ZDB-PUB-081121-6
Proper restoration of excitation-contraction coupling in the dihydropyridine receptor beta 1-null zebrafish relaxed is an exclusive function of the beta 1a subunit
Schredelseker, J., Dayal, A., Schwerte, T., Franzini-Armstrong, C., and Grabner, M.
Date: 2009
Source: The Journal of biological chemistry   284(2): 1242-1251 (Journal)
Registered Authors: Dayal, Anamika, Grabner, Manfred, Schredelseker, Johann, Schwerte, Thorsten
Keywords: none
MeSH Terms:
  • Animals
  • Animals, Genetically Modified
  • Calcium Channels, L-Type/deficiency*
  • Calcium Channels, L-Type/genetics
  • Calcium Channels, L-Type/metabolism*
  • Muscle Fibers, Skeletal/metabolism
  • Protein Binding
  • Protein Subunits/deficiency
  • Protein Subunits/genetics
  • Protein Subunits/metabolism
  • Zebrafish/genetics
  • Zebrafish/metabolism*
PubMed: 19008220 Full text @ J. Biol. Chem.
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ABSTRACT
The paralyzed zebrafish strain relaxed carries a null-mutation for the skeletal-muscle dihydropyridine receptor (DHPR) beta(1a) subunit. Lack of beta(1a) results in i) reduced membrane expression of the pore forming DHPR alpha(1S) subunit, ii) elimination of alpha(1S) charge movement, and iii) impediment of arrangement of the DHPRs in groups of four (tetrads) opposing the ryanodine receptor (RyR1) - a structural prerequisite for skeletal-muscle-type excitation-contraction (EC) coupling. In this study we used relaxed larvae and isolated myotubes as expression systems to discriminate specific functions of beta(1a) from rather general functions of beta isoforms. Zebrafish and mammalian beta(1a) subunits quantitatively restored alpha(1S) triad targeting and charge movement as well as intracellular Ca(2+) release, allowed arrangement of DHPRs in tetrads, and most strikingly recovered a fully motile phenotype in relaxed larvae. Interestingly, the cardiac/neuronal beta(2a) as the phylogenetically closest, and the ancestral housefly beta(M) as the most distant isoform to beta(1a) also completely recovered alpha(1S) triad expression and charge movement. However, both revealed drastically impaired intracellular Ca(2+) transients and very limited tetrad formation compared to beta(1a). Consequently, larval motility was either only partially restored (beta(2a))-injected larvae) or not restored at all (beta(M)). Thus, our results indicate that triad expression and facilitation of DHPR charge movement are common features of all tested beta subunits, while the efficient arrangement of DHPRs in tetrads and thus intact DHPR-RyR1 coupling is only promoted by the beta(1a) isoform. Consequently, we postulate a model that presents beta(1a) as an allosteric modifier of alpha(1S) conformation enabling skeletal-muscle-type EC coupling.
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