Abstract
Excessive reverse-mode (RM) sodium/calcium exchanger 1.1 (NCX1.1) activity, resulting from intracellular sodium accumulation caused by reduced Na+/K+-ATPase activity, increased Na-H exchanger 1 activity. The induction of the voltage-gated sodium channel late current component (late INa), is a major pathway for intracellular calcium (Ca2+i) loading in cardiac ischemia-reperfusion (IR) injury and cardiac glycoside toxicity. Inhibition of late INa with the antianginal agent ranolazine is protective in models of IR injury and cardiac glycoside toxicity. However, whether inhibition of late INa alone is sufficient to provide maximal protection or additional inhibition of RM NCX1.1 provides further benefit remains to be determined conclusively. Therefore, the effects of ranolazine were compared with the INa inhibitor lidocaine in models of IR injury and ouabain toxicity, RM NCX1.1-mediated Ca2+ overload, and patch-clamp assays of RM NCX1.1 currents. Ranolazine and lidocaine (10 μM) similarly reduced Ca2+i overload and improved left ventricle work recovery in whole-heart models of IR injury or exposure to ouabain (80 μM). Ranolazine (10 μM), but not lidocaine (10 μM), reduced RM NCX1.1-mediated Ca2+i overload in ventricular myocytes. Furthermore, ranolazine inhibited RM NCX1.1 currents (IC50 1.7 μM), without affecting forward mode currents, revealing that ranolazine has novel RM NCX1.1 inhibitory actions. However, because lidocaine provides similar protection to ranolazine in whole-heart models but does not inhibit RM NCX1.1, we conclude that induction of late INa is upstream of RM NCX1.1 activity and selective inhibition of late INa alone is sufficient to reduce Ca2+i overload and contractile dysfunction in IR injury and cardiac glycoside toxicity.
Footnotes
This work was supported by the Canadian Institutes of Health Research [Grants MOP-37945 (to P.E.L.); MOP-115055 (to A.S.C.)]; the Heart and Stroke Foundation of Alberta, the Northwest Territories and Nunavut. D.S. was supported by an Alberta Innovates Health Solutions trainee award. K.S.C.H. received support from the Canadian Institutes of Health Research Strategic Training Initiative for the study of membrane proteins. P.E.L. is the holder of the Charles A. Allard Chair in Diabetes Research and received salary support as an Alberta Innovates Health Solutions Senior Scholar.
Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
ABBREVIATIONS:
- Ca2+i
- intracellular calcium
- IR
- ischemia-reperfusion
- INa
- sodium current
- NCX1.1
- sodium/calcium exchanger 1.1
- RM
- reverse mode
- FM
- forward mode
- Na+i
- intracellular sodium
- NRVM
- neonatal rat ventricular myocyte
- DMSO
- dimethyl sulfoxide
- AUC
- area under the curve
- shRNA
- short hairpin RNA
- ANOVA
- analysis of variance
- LV
- left ventricle
- TTX
- tetrodotoxin
- CaMKII
- Ca2+/calmodulin-dependent kinase II
- TEA
- tetraethylammonium
- WT
- wild type
- F405/F585
- fluorescence at 405 nm/fluorescence at 485 nm
- KB-R7943
- 2-(2-(4-(4-nitrobenzyloxy)phenyl)ethyl)isothiourea methanesulfonate.
- Received May 30, 2012.
- Accepted August 8, 2012.
- Copyright © 2012 by The American Society for Pharmacology and Experimental Therapeutics
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