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Association of Calcium Channel α 1S and β 1a Subunits is Required for the Targeting of β 1a but not of α 1S into Skeletal Muscle Triads
Birgit Neuhuber, Uli Gerster, Frank Doring, Hartmut Glossmann, Tsutomu Tanabe and Bernhard E. Flucher
Proceedings of the National Academy of Sciences of the United States of America
Vol. 95, No. 9 (Apr. 28, 1998), pp. 5015-5020
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/44658
Page Count: 6
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The skeletal muscle L-type Ca2+ channel is a complex of five subunits that is specifically localized in the triad. Its primary function is the rapid activation of Ca2+ release from cytoplasmic stores in a process called excitation-contraction coupling. To study the role of α 1S-β 1a interactions in the incorporation of the functional channel complex into the triad, α 1S and β 1a [or a β 1a-green fluorescent protein (GFP) fusion protein] were expressed alone and in combination in myotubes of the dysgenic cell line GLT. β GFP expressed in dysgenic myotubes that lack the skeletal muscle α 1S subunit was diffusely distributed in the cytoplasm. On coexpression with the α 1S subunit β GEP distribution became clustered and colocalized with α 1S immunofluorescence. Based on the colocalization of β GFP and α 1S with the ryanodine receptor the clusters were identified as T-tubule/sarcoplasmic reticulum junctions. Expression of α 1S with and without β 1a restored Ca2+ currents and depolarization-induced Ca2+ release. The translocation of β GFP from the cytoplasm into the junctions failed when β GFP was coexpressed with α 1S mutants in which the β interaction domain had been altered (α 1S-Y366S) or deleted (α 1S-Δ 351-380). Although α 1S-Y366S did not associate with β GFP it was incorporated into the junctions, and it restored Ca2+ currents and depolarization-induced Ca2+ release. Thus, β 1a requires the association with the β interaction domain in the I-II cytoplasmic loop of α 1S for its own incorporation into triad junctions, but stable α 1S-β 1a association is not necessary for the targeting of α 1S into the triads or for its normal function in Ca2+ conductance and excitation-contraction coupling.
Proceedings of the National Academy of Sciences of the United States of America © 1998 National Academy of Sciences