Nerol Attenuates Ouabain-Induced Arrhythmias

Abstract

Nerol (C₁₀H₁₈O) is a monoterpene found in many essential oils, such as lemon balm and hop. In this study, we explored the contractile and electrophysiological properties of nerol and demonstrated its antiarrhythmic effects in guinea pig heart preparation. Nerol effects were evaluated on atrial and ventricular tissue contractility, electrocardiogram (ECG), voltage-dependent L-type Ca²⁺ current (I_Ca,L), and ouabain-triggered arrhythmias. Overall our results revealed that by increasing concentrations of nerol (from 0.001 to 30 mM) there was a significant decrease in left atrium contractile force. This effect was completely and rapidly reversible after washing out (~ 2 min). Nerol (at 3 mM concentration) decreased the left atrium positive inotropic response evoked by adding up CaCl₂ in the extracellular medium. Interestingly, when using a lower concentration of nerol (30 μM), it was not possible to clearly observe any significant ECG signal alterations but a small reduction of ventricular contractility was observed. In addition, 300 μM nerol promoted a significant decrease on the cardiac rate and contractility. Important to note is the fact that in isolated cardiomyocytes, peak I_Ca,L was reduced by 58.9 ± 6.31% after perfusing 300 μM nerol (n=7, p<0.05). Nerol, at 30 and 300 μM, delayed the time of onset of ouabain-triggered arrhythmias and provoked a decrease in the diastolic tension induced by the presence of ouabain (50 μM). Furthermore, nerol preincubation significantly attenuated arrhythmia severity index without changes in the positive inotropism elicited by ouabain exposure. Taken all together, we may be able to conclude that nerol primarily by reducing Ca²⁺ influx through L-type Ca²⁺ channel blockade lessened the severity of ouabain-triggered arrhythmias in mammalian heart.

Figure 1

Effects of nerol on the contractility of guinea pig left atrium and on the calcium influx. (a) Concentration-response curve for the negative inotropic effect of nerol (EC₅₀ = 1.94 ± 0.2 mM, n = 5). (b) Concentration-response curves of CaCl₂ in control situation and in the presence of nerol (n = 5). (c) Representative recording showing the L-type calcium currents (I_Ca,L) in control and 300 μM nerol. (d) Average effect of nerol on the I_Ca,L density (n = 7, ∗p<0.05). Data are represented as mean ± SEM. Paired Student's t-test.

Figure 2

Effect of nerol on the electrocardiographic parameters and left ventricular developed pressure (LVDP) in guinea pig isolated heart. (a) Representative traces of ECG in control (A), 30 μM (B), and 300 μM nerol (C). (b) Representative traces of LVDP in control (A), after 10 min of perfusion with 30 μM (B) and 300 μM (C) nerol. (c) Effect of nerol on the PR interval, (d) QTc interval, (e) QRS complex duration, (f) LVDP, and (g) heart rate (BPM). Data are represented as means ± SEM (n = 4-9, ∗p<0.05 versus control, #p<0.05 versus 30 μM nerol). One-way ANOVA followed by Tukey's post hoc test.

Figure 3

Protective effects of nerol on ouabain-induced arrhythmias in guinea pig hearts. (a) Representative recording of effects of ouabain (Ouab, 50 μM) on left ventricular developed pressure (LVDP, Top panel), nerol (30 and 300 μM) + ouabain (middle), and nifedipine (0.35 μM) + ouabain (botton). Summary of effects of nerol or nifedipine preincubation on the onset time of arrhythmia (b), inotropic response (c), tonotropic effect (d), and inotropic response rate (dP/dt) induced by ouabain (e), respectively. Data are represented as means ± SEM (n = 5 - 6, ∗p<0.05 versus Ouab). One-way ANOVA followed was by Tukey's post hoc test.

Figure 4

Nerol attenuates cardiac arrhythmias and electrocardiographic (ECG) alterations induced by ouabain. (a) Representative ECG recordings with 50 μM ouabain (Ouab) evoking the occurrence of ventricular premature beatings (VPB), ventricular tachycardia (VT), and ventricular fibrillation (VF). (b) Arrhythmias score and (c) occurrence of arrhythmias (VPB, VT, VF). ECG parameters: PR interval (d), QRS complex (e), and QTc interval (f). Data are represented as means ± SEM (n = 4-7, ∗p<0.05 versus control, # p<0.05 versus ouabain). One-way ANOVA followed by Tukey's post hoc test. Chi-squared test (c).