Protein kinases mediate anti-inflammatory effects of cannabidiol and estradiol against high glucose in cardiac sodium channels

Background and purpose. Cardiovascular anomalies are predisposing factors for diabetes-induced morbidity and mortality. Recently, we showed that high glucose induces changes in the biophysical properties of Nav1.5 that could be strongly correlated to diabetes-induced arrhythmia. However, the mechanisms underlying hyperglycemia-induced inflammation, and how inflammation provokes cardiac arrhythmia, are not well understood. We hypothesized that inflammation could mediate the high glucose-induced biophyscial changes on Nav1.5 through protein phosphorylation by protein kinases A and C. We also hypothesized that this signaling pathway is, at least partly, involved in the cardiprotective effects of CBD and E2. Experimental approach. To test these ideas, we used Chinese hamster ovarian (CHO) cells transiently co-transfected with cDNA encoding human Nav1.5 α-subunit under control, a cocktail of inflammatory mediators or 100 mM glucose conditions (for 24 hours). We used electrophysiological experiments and action potential modelling. Key Results. Inflammatory mediators, similar to 100 mM glucose, right shifted the voltage dependence of conductance and steady state fast inactivation and increased persistent current leading to computational prolongation of action potential (hyperexcitability) which could result in long QT3 arrhythmia. In addition, activators of PK-A or PK-C replicated the inflammation-induced gating changes of Nav1.5. Inhibitors of PK-A or PK-C, CBD or E2 mitigated all the potentially deleterious effects provoked by high glucose/inflammation. Conclusions and implications. These findings suggest that PK-A and PK-C may mediate the anti-inflammatory effects of CBD and E2 against high glucose-induced arrhythmia. CBD, via Nav1.5, may be a cardioprotective therapeutic approach in diabetic postmenopausal population.

Enhanced basal late sodium current appears to underlie the age-related prolongation of action potential duration in guinea pig ventricular myocytes

Aging hearts have prolonged QT interval and are vulnerable to oxidative stress. Because the QT interval indirectly reflects the action potential duration (APD), we examined the hypotheses that 1) the APD of ventricular myocytes increases with age; 2) the age-related prolongation of APD is due to an enhancement of basal late Na+ current ( INaL); and 3) inhibition of INaL may protect aging hearts from arrhythmogenic effects of hydrogen peroxide (H2O2). Experiments were performed on ventricular myocytes isolated from (young) 1-mo- and (old) 1-yr-old guinea pigs (GPs). The APD of myocytes from old GPs was significantly longer than that from young GPs and was shortened by the INaL inhibitors GS967 and tetrodotoxin. The magnitude of INaL was significantly larger in myocytes from old than from young GPs. The CaMKII inhibitors KN-93 and AIP and the NaV1.5-channel blocker methanethiosulfonate ethylammonium blocked the INaL. There were no significant differences between myocytes from young and old GPs in L-type Ca2+ current and the rapidly and slowly activating delayed rectifier K+ currents, although the inward rectifier K+ current was slightly decreased in myocytes from old GPs. H2O2 induced more early afterdepolarizations in myocytes from old than from young GPs. The effect of H2O2 was attenuated by GS967. The results suggest that 1) the APD of myocytes from old GPs is prolonged, 2) a CaMKII-mediated increase in NaV1.5-channel INaL is responsible for the prolongation of APD, and 3) inhibition of INaL may be beneficial for maintaining electrical stability under oxidative stress in myocytes of old GPs. NEW & NOTEWORTHY The action potential duration is significantly longer in ventricular myocytes from old than from young guinea pigs, which may explain, at the cellular level, the increase in QT interval with age. A CaMKII-mediated enhancement of NaV1.5-channel late current is responsible for the age-related prolongation of action potential duration. The enhanced basal late sodium current may predispose cardiac myocytes of old animals to oxidative stress and arrhythmogenesis.

Susceptibility of Diabetic Heart to Catecholamine-induced Arrhythmias is Independent of Contractile Dysfunction

ABSTRACT Background: Diabetes is associated with myocardial electrical instability and prolongation of action potential duration that result in disturbances in the rhythm of the heart. Objective: Th is study was undertaken to examine the role of circulating catecholamines in abnormal cardiac rhythm and contractility during diff erent stages of diabetes. Methods: Diabetes was induced in male Sprague-Dawley rats with streptozotocin (STZ; 65 mg/kg, i.v.). Epinephrine (4-128 μg/kg, i.v.) -induced arrhythmias and plasma levels of epinephrine (Epi) and norepinephrine (NE) were determined in control, 4- and 8-wk diabetic animals. Echocardiography was used to assess cardiac remodeling and contractile function. Results: Although diabetes induced cardiac dysfunction, there were no significant differences in cardiac output, ejection fraction, left ventricle (LV) dimensions, LV fractional shortening between the 4- and 8-wk diabetic animals. Th e electrocardiogram of both diabetic groups showed deep S wave as well as changes in T wave and ST segment. In addition, prolongation of the RR interval in the 4- and 8-wk diabetic animals was seen, while prolongation of the QT and PR intervals were only seen in the 8-wk diabetic animals. Th e severity of Epi-induced ventricular arrhythmias, as assessed by arrhythmia score, was significantly lower in the 8-wk diabetic rats, as compared to the 4-wk diabetic animals. Circulating Epi levels were significantly decreased in the 8-wk diabetic rats, whereas NE levels were increased in the 4-wk diabetic rats. Conclusions: Th e sensitivity of the diabetic heart to catecholamine- triggered arrhythmias may be dependent on circulating Epi rather than NE and thus it can be proposed that the increased incidence of sudden cardiac death in diabetics may not be associated with response to catecholamines.