Heparin Oligosaccharides Have Antiarrhythmic Effect by Accelerating the Sodium-Calcium Exchanger

Abstract

Background: Blockage of the Na⁺/Ca²⁺ exchanger (NCX) is used to determine the role of NCX in arrhythmogenesis. Trisulfated heparin disaccharide (TD) and Low Molecular Weight Heparins (LMWHs) can directly interact with the NCX and accelerate its activity. Objective: In this work, we investigated the antiarrhythmic effect of heparin oligosaccharides related to the NCX activity. Methods: The effects of heparin oligosaccharides were tested on the NCX current (patch clamping) and intracellular calcium transient in rat cardiomyocytes. The effects of heparin oligosaccharides were further investigated in arrhythmia induced in isolated rat atria and rats in vivo. Results: The intracellular Ca²⁺ concentration decreases upon treatment with either enoxaparin or ardeparin. These drugs abolished arrhythmia induction in isolated atria. The NCX antagonist KB-R7943 abolished the enoxaparin or ardeparin antiarrhythmic effects in isolated atria. In the in vivo measurements, injection of TD 15 min both before coronary occlusion or immediately after reperfusion, significantly prevented the occurrence of reperfusion-induced arrhythmias (ventricular arrhythmia and total AV block) and reduced the lethality rate. The patch clamping experiments showed that, mechanistically, TD increases the forward mode NCX current. Conclusion: Together, the data shows that heparin oligosaccharides may constitute a new class of antiarrhythmic drug that acts by accelerating the forward mode NCX under calcium overload.

Keywords: arrhythmia; calcium overload; low molecular weight heparin; sodium-calcium exchanger; trisulfated heparin disaccharide.

Scheme 1

Diagram of the experimental protocol for each route of drug administration in the rat. IV: intravenous.

Figure 1

Typical electrogram records of isolated rat atria submitted to the electric field stimulation (EFS) protocol. The effect of the EFS-protocol on atrial response was studied in the absence of any drug treatment (control, Left upper) as well as in the presence of 50 μM KB-R7943 alone (Right upper), 10 μM enoxaparin alone (Left lower) and the simultaneous presence of 50 μM KB-R7943 and 10 μM enoxaparin (Right lower). The sinus rates (Hz) prior to the EFS-protocol were 3.7, 3.6, 0.9, and 1.2 in control, enoxaparin alone, KB-R7943 alone and enoxaparin + KB-R 7043 groups, respectively. Accordingly, the atrial rates (Hz) following the EFS-protocol for these groups were 25, 5.8, 25, and 25, respectively.

Figure 2

(A,B) Calcium transients induced by Bay-K in either the absence (control) or presence of enoxaparin (ENOX 1 μM) or ardeparin (ARD 1 μM). (C) Calcium transient induced by Bay-K in the presence of either nifedipine alone (NIF 1 μM) or simultaneous presence of 1 μM NIF and 1 μM ENOX. (D,E) Calcium transients induced by the caffeine-ryanodine-thapsgargin cocktail (CRT) in either the absence (control) or presence of 1 μM ENOX or 1 μM ARD.

Figure 3

Effects of trisulfated heparin disaccharide (TD) on the NCX current (NCX) recorded from acutely isolated rat ventricular myocytes at various Ca_i (A: 300 nM; B: 400 nM and C: 600 nM). The graph (D) is % change obtained by dividing the current amplitude value at a given voltage for a given test compound concentration by the current value recorded in the absence of test compound (control).