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Syntaxin 1A regulation of weakly inactivating N‐type Ca 2+ channels
Author(s) -
Hurley Joyce H.,
Cahill Anne L.,
Wang Meijing,
Fox Aaron P.
Publication year - 2004
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2004.068817
Subject(s) - syntaxin , xenopus , protein subunit , chemistry , syntaxin 3 , microbiology and biotechnology , mutant , biophysics , biology , biochemistry , membrane protein , gene , membrane
N‐ and P/Q‐type Ca 2+ 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 Ca 2+ channels, syntaxin 1A co‐expression reduced current amplitudes, increased voltage‐dependent inactivation and/or enhanced G‐protein inhibition. However, these studies were conducted in Ca 2+ 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 Ca 2+ channel subunits involved. This study was undertaken to determine the effect of syntaxin 1A on this weakly inactivating Ca 2+ channel. Co‐expression of syntaxin 1A with the weakly inactivating bovine N‐type Ca 2+ 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 α 1B subunit, β 2a subunit and syntaxin 1A. We determined that the synprint site of α 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 Ca 2+ current by syntaxin 1A cannot explain the large suppression of Ca 2+ current observed. Of most significance, syntaxin 1A increased voltage‐dependent inactivation in channels containing mutant β 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 Ca 2+ channel.