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This Article Full Text Full Text (PDF) All Versions of this Article: 560/2/351    most recent jphysiol.2004.068817v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Hurley, J. H Articles by Fox, A. P Search for Related Content PubMed PubMed Citation Articles by Hurley, J. H Articles by Fox, A. P

¹ Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA
² Department of Neurobiology, Pharmacology and Physiology, University of Chicago, Chicago, IL 60637, USA

N- and P/Q-type Ca²⁺ channels are abundant in nerve terminals where they interact with proteins of the release apparatus, including syntaxin 1A and SNAP-25. In previous studies on N- or P/Q-type Ca²⁺ channels, syntaxin 1A co-expression reduced current amplitudes, increased voltage-dependent inactivation and/or enhanced G-protein inhibition. However, these studies were conducted in Ca²⁺ channels that exhibited significant voltage-dependent inactivation. We previously reported that N-type current in bovine chromaffin cells exhibits very little voltage-dependent inactivation and we identified the Ca²⁺ channel subunits involved. This study was undertaken to determine the effect of syntaxin 1A on this weakly inactivating Ca²⁺ channel. Co-expression of syntaxin 1A with the weakly inactivating bovine N-type Ca²⁺ channels in Xenopus oocytes did not appear to alter inactivation but dramatically reduced current amplitudes, without changing cell surface expression. To further understand the mechanisms of syntaxin 1A regulation of this weakly inactivating channel, we examined mutants of the _1B subunit, ß_2a subunit and syntaxin 1A. We determined that the synprint site of _1B and the C-terminal third of syntaxin 1A were necessary for the reduced current amplitude. In addition we show that enhanced G-protein-dependent modulation of the Ca²⁺ current by syntaxin 1A cannot explain the large suppression of Ca²⁺ current observed. Of most significance, syntaxin 1A increased voltage-dependent inactivation in channels containing mutant ß_2a subunits that cannot be palmitoylated. Our data suggest that changes in inactivation can not explain the reduction in current amplitude produced by co-expressing syntaxin and a weakly inactivating Ca²⁺ channel.

(Received 25 May 2004; accepted after revision 18 August 2004; first published online 19 August 2004)
Corresponding author J. H. Hurley: Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA. Email: johurley{at}iupui.edu

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