title: Syntaxin-1A inhibition of P-1075, cromakalim, and diazoxide actions on mouse cardiac ATP-sensitive potassium channel.
abstract: OBJECTIVE
  Syntaxin (Syn)-1A binds sulfonylurea receptor (SUR) nucleotide binding folds of cardiac myocyte (SUR2A) and islet beta-cells (SUR1) to inhibit ATP-sensitive potassium (K(ATP)) channels. We further reported that Syn-1A reduced the potency and efficacy of beta-cell-specific K(ATP) channel openers (KCOs). Here, we examined whether Syn-1A would influence non-specific (diazoxide) and SUR2-specific KCOs [N-cyano-N'-(1,1-dimethylpropyl)-N''-3-pyridylguanidine (P-1075) and cromakalim] on cardiac myocyte K(ATP) channels activation.
  
  
  RESULTS
  Confocal microscopy and Western blotting verified the presence of both Syn-1A and -1B expressions on rodent cardiac ventricular myocytes. Inside-out patch-clamp electrophysiology was utilized to examine the effects of these syntaxins on K(ATP) macroscopic currents activated by various KCOs from a stable cell line expressing the potassium inward rectifier 6.2 (Kir6.2)/SUR2A and from C57BL/6 male mouse ventricular myocytes. Syn-1A inhibited the current amplitude activated by P-1075, cromakalim and diazoxide via its H3 but not Habc domain. Syn-1B exhibited similar inhibitory effects on P-1075 activation of K(ATP) currents. In examining for direct effects of Syn-1A on the KCO binding to cardiac SUR2 receptors, we found that Syn-1A did not directly affect [(3)H]-P-1075 binding to rat cardiac membrane SUR2A at maximum binding capacity, but was able to mildly reduce the affinity of cold P-1075 and cromakalim to displace [(3)H]-P-1075 binding.
  
  
  CONCLUSIONS
  In conclusion, Syn-1A (and Syn-1B) could inhibit K(ATP) currents activated by SUR2A-acting KCOs. Potential fluctuations in the levels of these syntaxins in the myocardium may affect the therapeutic effectiveness of cardiac KCOs.
authors.affiliation: Department of Medicine, University of Toronto, Room 7310, Medical Sciences Building, Toronto, ON, Canada.
authors.forename: Betty
authors.initials: B
authors.lastname: Ng
authors.forename: Youhou
authors.initials: Y
authors.lastname: Kang
authors.forename: Huanli
authors.initials: H
authors.lastname: Xie
authors.forename: Hui
authors.initials: H
authors.lastname: Sun
authors.forename: Herbert Y
authors.initials: HY
authors.lastname: Gaisano
mesh_terms: D000818:Animals; D002460:Cell Line; D002478:Cells, Cultured; D019806:Cromakalim / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D003981:Diazoxide / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D006146:Guanidines / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D006801:Humans; D054086:KATP Channels / Q000187:drug effects* / Q000378:metabolism; D007668:Kidney / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D032383:Myocytes, Cardiac / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D018408:Patch-Clamp Techniques; D024661:Potassium Channels, Inwardly Rectifying / Q000187:drug effects / Q000378:metabolism; D011725:Pyridines / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D050827:Syntaxin 1 / Q000378:metabolism / Q000494:pharmacology*; D014665:Vasodilator Agents / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D000099161:Kcnj11 Channel
chemical_list: D019806:Cromakalim; D003981:Diazoxide; D006146:Guanidines; D054086:KATP Channels; D024661:Potassium Channels, Inwardly Rectifying; D011725:Pyridines; D050827:Syntaxin 1; D014665:Vasodilator Agents; D000099161:Kcnj11 Channel; C073896:N-cyano-N'-(1,1-dimethylpropyl)-N''-(3-pyridinyl)guanidine