Cardiovascular Research Advance Access originally published online on August 14, 2008
Cardiovascular Research 2008 80(3):365-374; doi:10.1093/cvr/cvn210
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Syntaxin-1A inhibition of P-1075, cromakalim, and diazoxide actions on mouse cardiac ATP-sensitive potassium channel
1 Department of Medicine, University of Toronto, Room 7310, Medical Sciences Building, Toronto, ON, Canada M5S 1A8
2 Department of Physiology, University of Toronto, Room 7310, Medical Sciences Building, Toronto, ON, Canada M5S 1A8
* Corresponding author. Tel: +1 416 978 1526; fax: +416 978 8765. E-mail address: herbert.gaisano{at}utoronto.ca
Aims: Syntaxin (Syn)-1A binds sulfonylurea receptor (SUR) nucleotide binding folds of cardiac myocyte (SUR2A) and islet β-cells (SUR1) to inhibit ATP-sensitive potassium (KATP) channels. We further reported that Syn-1A reduced the potency and efficacy of β-cell-specific KATP 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 KATP channels activation.
Methods and 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 KATP 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 KATP 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 [3H]-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 [3H]-P-1075 binding.
Conclusion: In conclusion, Syn-1A (and Syn-1B) could inhibit KATP 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.
KEYWORDS Syntaxin; P-1075; Cromakalim; Diazoxide; ATP-sensitive potassium channel; Potassium channel openers; Sulfonylurea receptor; Kir6.2; SUR
Time for primary review: 20 days