Effects of anandamide on potassium channels in rat ventricular myocytes: a suppression of Ito and augmentation of KATP channels

Endocannabinoid regulation of inward rectifier potassium (Kir) channels

The inward rectifier potassium channel Kir2.1 (KCNJ2) is an important regulator of resting membrane potential in both excitable and non-excitable cells. The functions of Kir2.1 channels are dependent on their lipid environment, including the availability of PI(4,5)P2, secondary anionic lipids, cholesterol and long-chain fatty acids acyl coenzyme A (LC-CoA). Endocannabinoids are a class of lipids that are naturally expressed in a variety of cells, including cardiac, neuronal, and immune cells. While these lipids are identified as ligands for cannabinoid receptors there is a growing body of evidence that they can directly regulate the function of numerous ion channels independently of CBRs. Here we examine the effects of a panel of endocannabinoids on Kir2.1 function and demonstrate that a subset of endocannabinoids can alter Kir2.1 conductance to varying degrees independently of CBRs. Using computational and Surface plasmon resonance analysis, endocannabinoid regulation of Kir2.1 channels appears to be the result of altered membrane properties, rather than through direct protein-lipid interactions. Furthermore, differences in endocannabinoid effects on Kir4.1 and Kir7.1 channels, indicating that endocannabinoid regulation is not conserved among Kir family members. These findings may have broader implications on the function of cardiac, neuronal and/or immune cells.

A review of the direct targets of the cannabinoids cannabidiol, Δ9-tetrahydrocannabinol, N-arachidonoylethanolamine and 2-arachidonoylglycerol

Marijuana has been used by humans for thousands of years for both medicinal and recreational purposes. This included the treatment of pain, inflammation, seizures, and nausea. In the 1960s, the structure of the principal psychoactive ingredient Δ9-tetrahydrocannabinol was determined, and over the next few decades, two cannabinoid receptors were characterized along with the human endocannabinoid system and what it affects. This includes metabolism, the cardiovascular and reproductive systems, and it is involved in such conditions as inflammation, cancer, glaucoma, and liver and musculoskeletal disorders. In the central nervous system, the endocannabinoid system has been linked to appetite, learning, memory, and conditions such as depression, anxiety, schizophrenia, stroke, multiple sclerosis, neurodegeneration, addiction, and epilepsy. It was the profound effectiveness of cannabidiol, a non-psychoactive ingredient of marijuana, to relieve the symptoms of Dravet syndrome, a severe form of childhood epilepsy, that recently helped spur marijuana research. This has helped substantially to change society's attitude towards this potential source of useful drugs. However, research has also revealed that the actions of endocannabinoids, such as anandamide and 2-arachidonoylglycerol, and the phytocannabinoids, tetrahydrocannabinol and cannabidiol, were not just due to interactions with the two cannabinoid receptors but by acting directly on many other targets including various G-protein receptors and cation channels, such as the transient receptor potential channels for example. This mini-review attempts to survey the effects of these 4 important cannabinoids on these currently identified targets.

Cardiotoxic effects of common and emerging drugs: role of cannabinoid receptors

Drug-induced cardiotoxicity has become one of the most common and detrimental health concerns, which causes significant loss to public health and drug resources. Cannabinoid receptors (CBRs) have recently achieved great attention for their vital roles in the regulation of heart health and disease, with mounting evidence linking CBRs with the pathogenesis and progression of drug-induced cardiotoxicity. This review aims to summarize fundamental characteristics of two well-documented CBRs (CB1R and CB2R) from aspects of molecular structure, signaling and their functions in cardiovascular physiology and pathophysiology. Moreover, we describe the roles of CB1R and CB2R in the occurrence of cardiotoxicity induced by common drugs such as antipsychotics, anti-cancer drugs, marijuana, and some emerging synthetic cannabinoids. We highlight the 'yin-yang' relationship between CB1R and CB2R in drug-induced cardiotoxicity and propose future perspectives for CBR-based translational medicine toward cardiotoxicity curation and clinical monitoring.

Arrhythmic Effects of Cannabis in Ischemic Heart Disease

Rationale: Cannabis use is increasing worldwide, especially among older individuals at risk for chronic ischemic heart disease (IHD). However, little is known about the arrhythmic effects of cannabis use in IHD. Accordingly, we prospectively assessed the relationship between cannabis use, heart rate (HR), and arrhythmias in healthy age-matched controls and subjects with IHD. Methods: Healthy controls (n=37, 57% men) and subjects with IHD (myocardial infarction ≥3 months ago; n=24, 58% men) who used cannabis wore a Zio® (iRhythm Technologies) monitor for 14 days. Noncannabis using ischemic subjects (n=35, 51% males) wore Zio monitors for standard clinical indications. Baseline HR was compared with average HR measured for 4 h following consumption and changes in HR and frequency of arrhythmias were correlated with cannabis use. Results: In controls, HR increased 20 min (4.99±6.7 bpm, p=0.08) after use, then declined 4 h following use (-7.4±7.7, p<0.001). Conversely, subjects with IHD showed minimal HR increase (1.6±3.9 bpm) and blunted HR decline (-3.4±5.6 bpm, p<0.001). Supraventricular tachycardia (SVT) (29.7% vs. 58.3%; p=0.04) and nonsustained ventricular tachycardia (NSVT) (5.6% vs. 47.8%, p=0.01) were the most frequently occurring arrhythmias in controls and IHD subjects, respectively. Incidence of SVT decreased as cannabis use increased in both groups. Conversely, NSVT tended to increase with increased use in controls, and was significantly more prevalent in IHD. However, overall arrhythmia burden did not differ between cannabis users and nonusers with IHD. Conclusion: Our findings demonstrate that chronic cannabis use is associated with only mild HR changes, which are blunted in IHD. In addition, our data suggest that among cannabis users, arrhythmias are more frequent in IHD subjects that in healthy subjects.

Why Do Marijuana and Synthetic Cannabimimetics Induce Acute Myocardial Infarction in Healthy Young People?

The use of cannabis preparations has steadily increased. Although cannabis was traditionally assumed to only have mild vegetative side effects, it has become evident in recent years that severe cardiovascular complications can occur. Cannabis use has recently even been added to the risk factors for myocardial infarction. This review is dedicated to pathogenetic factors contributing to cannabis-related myocardial infarction. Tachycardia is highly important in this respect, and we provide evidence that activation of CB₁ receptors in brain regions important for cardiovascular regulation and of presynaptic CB₁ receptors on sympathetic and/or parasympathetic nerve fibers are involved. The prototypical factors for myocardial infarction, i.e., thrombus formation and coronary constriction, have also been considered, but there is little evidence that they play a decisive role. On the other hand, an increase in the formation of carboxyhemoglobin, impaired mitochondrial respiration, cardiotoxic reactions and tachyarrhythmias associated with the increased sympathetic tone are factors possibly intensifying myocardial infarction. A particularly important factor is that cannabis use is frequently accompanied by tobacco smoking. In conclusion, additional research is warranted to decipher the mechanisms involved, since cannabis use is being legalized increasingly and Δ⁹-tetrahydrocannabinol and its synthetic analogue nabilone are indicated for the treatment of various disease states.

Potassium channels as molecular targets of endocannabinoids

Endocannabinoids are a group of endogenous mediators derived from membrane lipids, which are implicated in a wide variety of physiological functions such as blood pressure regulation, immunity, pain, memory, reward, perception, reproduction, and sleep. N-Arachidonoylethanolamine (anandamide; AEA) and 2-arachidonoylglycerol (2-AG) represent two major endocannabinoids in the human body and they exert many of their cellular and organ system effects by activating the Gi/o protein-coupled, cannabinoid type 1 (CB1) and type 2 (CB2) receptors. However, not all effects of cannabinoids are ascribable to their interaction with CB1 and CB2 receptors; indeed, macromolecules like other types of receptors, ion channels, transcription factors, enzymes, transporters, and cellular structure have been suggested to mediate the functional effects of cannabinoids. Among the proposed molecular targets of endocannabinoids, potassium channels constitute an intriguing group, because these channels not only are crucial in shaping action potentials and controlling the membrane potential and cell excitability, thereby regulating a wide array of physiological processes, but also serve as potential therapeutic targets for the treatment of cancer and metabolic, neurological and cardiovascular disorders. This review sought to survey evidence pertaining to the CB1 and CB2 receptor-independent actions of endocannabinoids on ion channels, with an emphasis on AEA and potassium channels. To better understand the functional roles as well as potential medicinal uses of cannabinoids in human health and disease, further mechanistic studies to delineate interactions between various types of cannabinoids and ion channels, including members in the potassium channel superfamily, are warranted.

The electrophysiological effects of cannabidiol on action potentials and transmembrane potassium currents in rabbit and dog cardiac ventricular preparations

Cannabis use is associated with known cardiovascular side effects such as cardiac arrhythmias or even sudden cardiac death. The mechanisms behind these adverse effects are unknown. The aim of the present work was to study the cellular cardiac electrophysiological effects of cannabidiol (CBD) on action potentials and several transmembrane potassium currents, such as the rapid (I_Kr) and slow (I_Ks) delayed rectifier, the transient outward (I_to) and inward rectifier (I_K1) potassium currents in rabbit and dog cardiac preparations. CBD increased action potential duration (APD) significantly in both rabbit (from 211.7 ± 11.2. to 224.6 ± 11.4 ms, n = 8) and dog (from 215.2 ± 9.0 to 231.7 ± 4.7 ms, n = 6) ventricular papillary muscle at 5 µM concentration. CBD decreased I_Kr, I_Ks and I_to (only in dog) significantly with corresponding estimated EC₅₀ values of 4.9, 3.1 and 5 µM, respectively, without changing I_K1. Although the EC₅₀ value of CBD was found to be higher than literary C_max values after CBD smoking and oral intake, our results raise the possibility that potassium channel inhibition by lengthening cardiac repolarization might have a role in the possible proarrhythmic side effects of cannabinoids in situations where CBD metabolism and/or the repolarization reserve is impaired.

The electrophysiological effect of cannabidiol on hERG current and in guinea-pig and rabbit cardiac preparations

Cannabis use is associated with cardiovascular adverse effects ranging from arrhythmias to sudden cardiac death. The exact mechanism of action behind these activities is unknown. The aim of our work was to study the effect of cannabidiol (CBD), tetrahydrocannabinol and 11-nor-9-carboxy-tetrahydrocannabinol on cellular cardiac electrophysiological properties including ECG parameters, action potentials, hERG and I_Kr ion channels in HEK cell line and in rabbit and guinea pig cardiac preparations. CBD increased action potential duration in rabbit and guinea pig right ventricular papillary muscle at lower concentrations (1 µM, 2.5 µM and 5 µM) but did not significantly change it at 10 µM. CBD at high concentration (10 µM) decreased inward late sodium and L-type calcium currents as well. CBD inhibited hERG potassium channels with an IC₅₀ value of 2.07 µM at room temperature and delayed rectifier potassium current with 6.5 µM at 37 °C, respectively. The frequency corrected QT interval (QT_c) was significantly lengthened in anaesthetized guinea pig without significantly changing other ECG parameters. Although the IC₅₀ value of CBD was higher than literary C_max values after CBD smoking and oral intake, our results raise the possibility that hERG and potassium channel inhibition might have a role in the possible proarrhythmic adverse effects of cannabinoids in situations where metabolism of CBD impaired and/or the repolarization reserve is weakened.

Mechanisms for the Risk of Acute Coronary Syndrome and Arrhythmia Associated With Phytogenic and Synthetic Cannabinoid Use

Phytogenic cannabinoids from Cannabis sativa and synthetic cannabinoids are commonly used substances for their recreational and medicinal properties. There are increasing reports of cardiotoxicity in close temporal association with cannabinoid use in patients with structurally normal hearts and absence of coronary arterial disease. Associated adverse events include myocardial ischemia, conduction abnormalities, arrhythmias, and sudden death. This review details the effects of phytogenic and synthetic cannabinoids on diverse receptors based on evidence from in vitro, human, and animal studies to establish a molecular basis for these deleterious clinical effects. The synergism between endocannabinoid dysregulation, cannabinoid receptor, and noncannabinoid receptor binding, and impact on cellular ion flux and coronary microvascular circulation is delineated. Pharmacogenetic factors placing certain patients at higher risk for cardiotoxicity are also correlated with the diverse effects of cannabinoids.

ABHD6: Its Place in Endocannabinoid Signaling and Beyond

The endocannabinoid (eCB) signaling system modulates neurotransmission and inflammation, among other physiological functions. Its newest member, α/β-hydrolase domain-containing 6 (ABHD6), has emerged as a promising therapeutic target to treat several devastating diseases, including epilepsy. Here, we review the molecular mechanisms that mediate and control eCB signaling and, within it, the specific role of ABHD6. We also discuss how ABHD6 controls the abundance of additional lipids and the trafficking of ionotropic receptors to plasma membranes. We finish with several unexplored questions regarding this novel enzyme. Our current understanding of the molecular mechanism and biological function of ABHD6 provides a strong foundation for the development of small-molecule therapeutics to treat devastating diseases.

Cannabinoids and Cardiovascular System

Cannabinoids influence cardiovascular variables in health and disease via multiple mechanisms. The chapter covers the impact of cannabinoids on cardiovascular function in physiology and pathology and presents a critical analysis of the proposed signalling pathways governing regulation of cardiovascular function by endogenously produced and exogenous cannabinoids. We know that endocannabinoid system is overactivated under pathological conditions and plays both a protective compensatory role, such as in some forms of hypertension, atherosclerosis and other inflammatory conditions, and a pathophysiological role, such as in disease states associated with excessive hypotension. This chapter focuses on the mechanisms affecting hemodynamics and vasomotor effects of cannabinoids in health and disease states, highlighting mismatches between some studies. The chapter will first review the effects of marijuana smoking on cardiovascular system and then describe the impact of exogenous cannabinoids on cardiovascular parameters in humans and experimental animals. This will be followed by analysis of the impact of cannabinoids on reactivity of isolated vessels. The article critically reviews current knowledge on cannabinoid induction of vascular relaxation by cannabinoid receptor-dependent and -independent mechanisms and dysregulation of vascular endocannabinoid signaling in disease states.

Cytosolic increased labile Zn2+ contributes to arrhythmogenic action potentials in left ventricular cardiomyocytes through protein thiol oxidation and cellular ATP depletion

Intracellular labile (free) Zn²⁺-level ([Zn²⁺]_i) is low and increases markedly under pathophysiological conditions in cardiomyocytes. High [Zn²⁺]_i is associated with alterations in excitability and ionic-conductances while exact mechanisms are not clarified yet. Therefore, we examined the elevated-[Zn²⁺]_i on some sarcolemmal ionic-mechanisms, which can mediate cardiomyocyte dysfunction. High-[Zn²⁺]_i induced significant changes in action potential (AP) parameters, including depolarization in resting membrane-potential and prolongations in AP-repolarizing phases. We detected also the time-dependent effects such as induction of spontaneous APs at the time of ≥ 3 min following [Zn²⁺]_i increases, a manner of cellular ATP dependent and reversible with disulfide-reducing agent dithiothreitol, DTT. High-[Zn²⁺]_i induced inhibitions in voltage-dependent K⁺-channel currents, such as transient outward K⁺-currents, I_to, steady-state currents, I_ss and inward-rectifier K⁺-currents, I_K1, reversible with DTT seemed to be responsible from the prolongations in APs. We, for the first time, demonstrated that lowering cellular ATP level induced significant decreaeses in both I_ss and I_K1, while no effect on I_to. However, the increased-[Zn²⁺]_i could induce marked activation in ATP-sensitive K⁺-channel currents, I_KATP, depending on low cellular ATP and thiol-oxidation levels of these channels. The mRNA levels of Kv4.3, Kv1.4 and Kv2.1 were depressed markedly with increased-[Zn²⁺]_i with no change in mRNA level of Kv4.2, while the mRNA level of I_KATP subunit, SUR2A was increased significantly with increased-[Zn²⁺]_i, being reversible with DTT. Overall we demonstrated that high-[Zn²⁺]_i, even if nanomolar levels, alters cardiac function via prolonged APs of cardiomyocytes, at most, due to inhibitions in voltage-dependent K⁺-currents, although activation of I_KATP is playing cardioprotective role, through some biochemical changes in cellular ATP- and thiol-oxidation levels. It seems, a well-controlled [Zn²⁺]_i can be novel therapeutic target for cardiac complications under pathological conditions including oxidative stress.

Addictive drugs, arrhythmias, and cardiac inward rectifiers

In many addictive drugs including alcohol and nicotine, proarrhythmic effects were reported. This review provides an overview of the current knowledge in this field (with a focus on the inward rectifier potassium currents) to promote the lacking data and appeal for their completion, thus, to improve understanding of the proarrhythmic potential of addictive drugs.

Cardioprotective effects of fatty acid amide hydrolase inhibitor URB694, in a rodent model of trait anxiety

In humans, chronic anxiety represents an independent risk factor for cardiac arrhythmias and sudden death. Here we evaluate in male Wistar rats bred for high (HAB) and low (LAB) anxiety-related behavior, as well as non-selected (NAB) animals, the relationship between trait anxiety and cardiac electrical instability and investigate whether pharmacological augmentation of endocannabinoid anandamide-mediated signaling exerts anxiolytic-like and cardioprotective effects. HAB rats displayed (i) a higher incidence of ventricular tachyarrhythmias induced by isoproterenol, and (ii) a larger spatial dispersion of ventricular refractoriness assessed by means of an epicardial mapping protocol. In HAB rats, acute pharmacological inhibition of the anandamide-degrading enzyme, fatty acid amide hydrolase (FAAH), with URB694 (0.3 mg/kg), (i) decreased anxiety-like behavior in the elevated plus maze, (ii) increased anandamide levels in the heart, (iii) reduced isoproterenol-induced occurrence of ventricular tachyarrhythmias, and (iv) corrected alterations of ventricular refractoriness. The anti-arrhythmic effect of URB694 was prevented by pharmacological blockade of the cannabinoid type 1 (CB₁), but not of the CB₂, receptor. These findings suggest that URB694 exerts anxiolytic-like and cardioprotective effects in HAB rats, the latter via anandamide-mediated activation of CB₁ receptors. Thus, pharmacological inhibition of FAAH might be a viable pharmacological strategy for the treatment of anxiety-related cardiac dysfunction.

Pharmacological evaluation of R(+)-pulegone on cardiac excitability: role of potassium current blockage and control of action potential waveform

INTRODUCTION

R(+)-pulegone is a ketone monoterpene and it is the main constituent of essential oils in several plants. Previous studies provided some evidence that R(+)-pulegone may act on isolated cardiac myocytes. In this study, we evaluated in extended detail, the pharmacological effects of R(+)-pulegone on cardiac tissue.

METHODS

Using in vivo measurements of rat cardiac electrocardiogram (ECG) and patch-clamp technique in isolated myocytes we determinate the influence of R(+)-pulegone on cardiac excitability.

RESULTS

R(+)-pulegone delayed action potential repolarization (APR) in a concentration-dependent manner (EC50=775.7±1.48, 325.0±1.30, 469.3±1.91 μM at 10, 50 and 90% of APR respectively). In line with prolongation of APR R(+)-pulegone, in a concentration-dependent manner, blocked distinct potassium current components (transient outward potassium current (I(to)), rapid delayed rectifier potassium current (I(Kr)), inactivating steady state potassium current (I(ss)) and inward rectifier potassium current (I(K1))) (EC50=1441±1.04; 605.0±1.22, 818.7±1.22; 1753±1.09 μM for I(to), I(Kr), I(ss) and I(K1), respectively). The inhibition occurred in a fast and reversible way, without changing the steady-state activation curve, but instead shifting to the left the steady-state inactivation curve (V1/2 from -56.92±0.35 to -67.52±0.19 mV). In vivo infusion of 100 mg/kg R(+)-pulegone prolonged the QTc (∼40%) and PR (∼62%) interval along with reducing the heart rate by ∼26%.

CONCLUSION

Taken together, R(+)-pulegone prolongs the APR by inhibiting several cardiomyocyte K(+) current components in a concentration-dependent manner. This occurs through a direct block by R(+)-pulegone of the channel pore, followed by a left shift on the steady state inactivation curve. Finally, R(+)-pulegone induced changes in some aspects of the ECG profile, which are in agreement with its effects on potassium channels of isolated cardiomyocytes.

Regulatory effects of anandamide on intracellular Ca(2+) concentration increase in trigeminal ganglion neurons

Activation of cannabinoid receptor type 1 on presynaptic neurons is postulated to suppress neurotransmission by decreasing Ca²⁺ influx through high voltage-gated Ca²⁺ channels. However, recent studies suggest that cannabinoids which activate cannabinoid receptor type 1 can increase neurotransmitter release by enhancing Ca²⁺ influx in vitro. The aim of the present study was to investigate the modulation of intracellular Ca²⁺ concentration by the cannabinoid receptor type 1 agonist anandamide, and its underlying mechanisms. Using whole cell voltage-clamp and calcium imaging in cultured trigeminal ganglion neurons, we found that anandamide directly caused Ca²⁺ influx in a dose-dependent manner, which then triggered an increase of intracellular Ca²⁺ concentration. The cyclic adenosine and guanosine monophosphate-dependent protein kinase systems, but not the protein kinase C system, were involved in the increased intracellular Ca²⁺ concentration by anandamide. This result showed that anandamide increased intracellular Ca²⁺ concentration and inhibited high voltage-gated Ca²⁺ channels through different signal transduction pathways.

Long‑term treatment of spontaneously hypertensive rats with losartan and molecular basis of modulating Ito of ventricular myocytes

The present study aimed to determine the effect of chronic treatment with losartan on transient outward potassium current (Ito) and the expression levels of potassium voltage-gated channel subfamily D members 2 and 3 (Kv4.2 and 3) and voltage-gated potassium channel-interacting protein 2 (KChIP2) in rats. Spontaneously hypertensive (SH) rats and Wistar-Kyoto (WKY) rats were used in the study. The rats were divided into lo-SH and SH groups and los-WKY and WKY groups, respectively. Ito was recorded and expression levels of Kv4.2, Kv4.3 and KChIP2 were measured by western blot analysis and quantitative polymerase chain reaction. Ito current density was smaller in SH compared with WKY, los-WKY and los-SH groups (P<0.01). Inactivation time constant of myocytes was larger in SH compared with WKY, los-WKY and los-SH groups (P<0.01). The mean levels of mRNA and protein of Kv4.2 and Kv4.3 were significantly lower in the SH compared with WKY, los-WKY and los‑SH groups in vivo and in vitro (P<0.01). The Pearson statistical test showed no correlation between the expression levels of Kv4.2, Kv4.3, KChIP2 and the changes in blood pressure in the losartan treatment group. In conclusion, chronic blockade of angiotensin II type 1 receptors with losartan reversed SH rats' electrical remodeling and shortened action potential duration, which was associated with an increase in Ito density as the expression levels of Kv4.2, Kv4.3 increased and the expression levels of KChIP2 decreased. However, the expression levels of Kv4.2, Kv4.3 and KChIP2 were not correlated with the change in blood pressure in the losartan treatment group. Losartan may decrease the inactivation time by increasing the expression of KChIP2.

Endocannabinoid system as a potential mechanism for n-3 long-chain polyunsaturated fatty acid mediated cardiovascular protection

The presence of an active and functioning endocannabinoid (EC) system within cardiovascular tissues implies that this system has either a physiological or pathophysiological role (or both), and there is a substantial literature to support the notion that, in the main, they are protective in the setting of various CVD states. Moreover, there is an equally extensive literature to demonstrate the cardio- and vasculo-protective effects of n-3 long-chain (LC)-PUFA. It is now becoming evident that there appears to be a close relationship between dietary intervention with n-3 LC-PUFA and changes in tissue levels of EC, raising the question as to whether or not EC may, at least in part, play a role in mediating the cardio-and vasculo-protective effects of n-3 LC-PUFA. This brief review summarises the current understanding of how both EC and n-3 LC-PUFA exert their protective effects in three major cardiovascular disorders (hypertension, atherosclerosis and acute myocardial infarction) and attempts to identify the similarities and differences that may indicate common or integrated mechanisms. From the data available, it is unlikely that in hypertension EC mediate any beneficial effects of n-3 LC-PUFA, since they do not share common mechanisms of blood pressure reduction. However, inhibition of inflammation is an effect shared by EC and n-3 LC-PUFA in the setting of both atherosclerosis and myocardial reperfusion injury, while blockade of L-type Ca2+ channels is one of the possible common mechanisms for their antiarrhythmic effects. Although both EC and n-3 LC-PUFA demonstrate vasculo- and cardio-protection, the literature overwhelmingly shows that n-3 LC-PUFA decrease tissue levels of EC through formation of EC–n-3 LC-PUFA conjugates, which is counter-intuitive to an argument that EC may mediate the effects of n-3 LC-PUFA. However, the discovery that these conjugates have a greater affinity for cannabinoid receptors than the native EC provides a fascinating avenue for further research into novel approaches for the treatment and prevention of atherosclerosis and myocardial injury following ischaemia/reperfusion.

Anandamide reduces intracellular Ca2+ concentration through suppression of Na+/Ca2+ exchanger current in rat cardiac myocytes

Purpose

Anandamide, one of the endocannabinoids, has been reported to exhibit cardioprotective properties, particularly in its ability to limit the damage produced by ischemia reperfusion injury. However, the mechanisms underlying the effect are not well known. This study is to investigate whether anandamide alter Na⁺/Ca²⁺ exchanger and the intracellular free Ca²⁺ concentration ([Ca²⁺]_i).

Methods

Na⁺/Ca²⁺ exchanger current (I_NCX) was recorded and analysed by using whole-cell patch-clamp technique and [Ca²⁺]_i was measured by loading myocytes with the fluorescent Ca²⁺ indicator Fura-2/AM.

Results

We found that I_NCX was enhanced significantly after perfusion with simulated ischemic external solution; [Ca²⁺]_i was also significantly increased by simulated ischemic solution. The reversal potential of I_NCX was shifted to negative potentials in simulated ischemic external solution. Anandamide (1–100 nM) failed to affect I_NCX and [Ca²⁺]_i in normal solution. However, anandamide (1–100 nM) suppressed the increase in I_NCX in simulated ischemic external solution concentration-dependently and normalized I_NCX reversal potential. Furthermore, anandamide (100 nM) significantly attenuated the increase in [Ca²⁺]_i in simulated ischemic solution. Blocking CB1 receptors with the specific antagonist AM251 (500 nM) failed to affect the effects of anandamide on I_NCX and [Ca²⁺]_i in simulated ischemic solution. CB2 receptor antagonist AM630 (100 nM) eliminated the effects of anandamide on I_NCX and [Ca²⁺]_i in simulated ischemic solution, and CB2 receptor agonist JWH133 (100 nM) simulated the effects of anandamide that suppressed the increase in I_NCX and [Ca²⁺]_i in simulated ischemic solution. In addition, pretreatment with the Gi/o-specific inhibitor pertussis toxin (PTX, 500 ng/ml) eliminated the effects of anandamide and JWH133 on I_NCX in simulated ischemic solution.

Conclusions

Collectively, these findings suggest that anandamide suppresses calcium overload through inhibition of I_NCX during perfusion with simulated ischemic solution; the effects may be mediated by CB2 receptor via PTX-sensitive Gi/o proteins. This mechanism is importantly involved in the anti-ischemia injury caused by endocannabinoids.