The C terminus of the Ca channel alpha1B subunit mediates selective inhibition by G-protein-coupled receptors.
Inhibition of calcium channels by G-protein-coupled receptors depends on the nature of the Galpha subunit, although the Gbetagamma complex is thought to be responsible for channel inhibition. Ca currents in hypothalamic neurons and N-type calcium channels expressed in HEK-293 cells showed robust inhibition by G(i)/G(o)-coupled galanin receptors (GalR1), but not by Gq-coupled galanin receptors (GalR2). However, deletions in the C terminus of alpha(1B-1) produced Ca channels that were inhibited after activation of both GalR1 and GalR2. Inhibition of protein kinase C (PKC) also revealed Ca current modulation by GalR2. Imaging studies using green fluorescent protein fusions of the C terminus of alpha(1B) demonstrated that activation of the GalR2 receptor caused translocation of the C terminus of alpha(1B-1) to the membrane and co-localization with Galphaq and PKC. Similar translocation was not seen with a C-terminal truncated splice variant, alpha(1B-2). Immunoprecipitation experiments demonstrated that Galphaq interacts directly with the C terminus of the alpha(1B) subunit. These results are consistent with a model in which local activation of PKC by channel-associated Galphaq blocks modulation of the channel by Gbetagamma released by Gq-coupled receptors.
Simen
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Department of Neurobiology, Pharmacology, and Physiology, University of Chicago, Chicago, Illinois 60637, USA.
Lee
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Simen
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Bindokas
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Miller
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RJ
D000818:Animals; D020864:Calcium Channels, N-Type / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002469:Cell Separation; D004594:Electrophysiology; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D019004:Galanin / Q000378:metabolism; D049452:Green Fluorescent Proteins; D020962:Heterotrimeric GTP-Binding Proteins / Q000378:metabolism; D006801:Humans; D007031:Hypothalamus; D066298:In Vitro Techniques; D007668:Kidney / Q000166:cytology / Q000378:metabolism; D008164:Luminescent Proteins / Q000235:genetics; D009433:Neural Inhibition / Q000502:physiology; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D011485:Protein Binding; D011493:Protein Kinase C / Q000378:metabolism; D021122:Protein Subunits; D021381:Protein Transport; D051381:Rats; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D044088:Receptors, Galanin; D018013:Receptors, Neuropeptide / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D013329:Structure-Activity Relationship; D014162:Transfection
D020864:Calcium Channels, N-Type; D008164:Luminescent Proteins; D021122:Protein Subunits; D011956:Receptors, Cell Surface; D044088:Receptors, Galanin; D018013:Receptors, Neuropeptide; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D019004:Galanin; D011493:Protein Kinase C; D019204:GTP-Binding Proteins; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D020962:Heterotrimeric GTP-Binding Proteins