Copyright © 2006, European Society of Cardiology
Differential sensitivities of the NCX1.1 and NCX1.3 isoforms of the Na+–Ca2+ exchanger to 
-linolenic acid
aCanadian Centre for Agri-Food Research in Health and Medicine, Winnipeg, Canada
bInstitute of Cardiovascular Sciences, St. Boniface General Hospital Research Centre, Winnipeg, Canada
cDepartment of Physiology, Faculty of Medicine, University of Manitoba, Winnipeg, Canada
dDepartment of Physiology, Faculties of Medicine and Pharmacy, University of Manitoba, Winnipeg, Canada
* Corresponding author. St. Boniface General Hospital Research Centre, 351 Taché Avenue, Winnipeg, MB, Canada, R2H 2A6. Tel.: +1 204 235 3206; fax: +1 204 231 1151. Email address: gpierce{at}sbrc.ca alukas{at}shaw.ca
Objective: Dietary intake of 
-3 polyunsaturated fatty acids (PUFA) like 
-linolenic acid (ALA) is antiarrhythmic and cardioprotective. PUFA may also be beneficial in hypertension. Altered Na+–Ca2+ exchanger (NCX) activity has been implicated in arrhythmias, hypertension and heart failure and may be a target for PUFA. Thus, we tested the effects of ALA and other distinct fatty acids on the cardiac (NCX1.1) and vascular (NCX1.3) NCX isoforms.
Methods: HEK293 cells stably expressing NCX isoforms were ramped from +60 to –100 mV (over 1600 ms) in the absence and presence of 25 µM oleic acid (OA, -9), linoleic acid (LA, -6), ALA (-3), or eicosapentaenoic acid (EPA, -3). NiCl2 (5 mM) was used to inhibit and therefore identify the NCX current. The effect of 25 µM ALA on NCX1.1 and NCX1.3 activity was also assessed in adult rat ventricular cardiomyocytes and rabbit aortic vascular smooth muscle cells (VSMC) by measuring [Ca2+]i following substitution of [Na+]o with Li+.
Results: Application of Ni2+ had no effect in non-transfected cells. ALA and EPA (25 µM) reduced the Ni2+-sensitive forward NCX1.1 current (at –100 mV) by 64% and reverse current (at +60 mV) by 57%, and inhibited the Ni2+-sensitive NCX1.3 forward and reverse currents by 79% and 76%, respectively. Neither OA nor LA (25 µM) affected the NCX1.1 currents, but both partially inhibited the forward and reverse mode NCX1.3 currents. Inhibition of NCX1.3 by ALA occurred at a much lower IC50 (
19 nM) than for NCX1.1 (120 nM). In cardiomyocytes and VSMC, ALA significantly reduced the Li+-induced rise in intracellular [Ca2+].
Conclusions: NCX1.3 is more sensitive to inhibition by ALA than NCX1.1. In addition, only -3 PUFA inhibits NCX1.1, but several classes of fatty acids inhibit NCX1.3. The differential sensitivity of NCX isoforms to fatty acids may have important implications as therapeutic approaches for hypertension, heart failure and arrhythmias.
KEYWORDS Na/Ca-exchanger; Hypertension; Ion exchangers; Antihypertensive agents; Antiarrhythmic agents
1 Current address: Howard Hughes Medical Institute, Department of Biological Chemistry, University of California, Los Angeles, United States.