Key result
Streptozotocin-induced diabetes cuts ventricular HCN2 mRNA expression ~60% in rats.
Why the study?
Despite disrupted repolarization, diabetic hearts sometimes show reduced ventricular arrhythmogenesis, prompting the hypothesis that myocardial alterations in HCN2 and HCN4 channels occur under hyperglycaemia.
Does STZ-induced diabetes alter the expression of HCN channels and cardiac repolarization in rat ventricles?
Does STZ-induced diabetes alter the expression of HCN channels and cardiac repolarization in rat ventricles?
Downregulation of HCN2 channels in the ventricles of diabetic rats suggests they may be part of ventricular electric remodeling and play a role in the altered arrhythmogenic profile of the diabetic heart.
Answers are grounded in this paper and cite their sources.
May link to diabetic ventricular arrhythmogenesis; hypothesis-generating and leaves open human translation.
Background In spite of disrupted repolarization of diabetic heart, some studies report less tendency of diabetic heart to develop ventricular arrhythmias suggesting effective compensatory mechanism. We hypothesized that myocardial alterations in HCN2 and HCN4 channels occur under hyperglycaemia. Methods Diabetes was induced in rats using a single injection of streptozotocin (STZ; 55 mg/kg body weight, i.p.). Basal ECG was measured. Expression of mRNA for HCN channels, potassium channels and microRNA 1 and 133a were measured in ventricular tissues. Protein expression of HCN2 channel isoform was assessed in five different regions of the heart by western blotting. Differentiated H9c2 cell line was used to examine HCN channels expression under hyperglycaemia in vitro. Results Six weeks after STZ administration, heart rate was reduced, QRS complex duration, QT interval and T-wave were prolonged in diabetic rats compared to controls. mRNA and protein expressions of HCN2 decreased exclusively in the ventricles of diabetic rats. HCN2 expression levels in atria of STZ rats and H9c2 cells treated with excess of glucose were not changed. MicroRNA levels were stable in STZ rat hearts. We found significantly decreased mRNA levels of several potassium channels participating in repolarization, namely Kcnd2 ( I to1 ), Kcnh2 ( I Kr ), Kcnq1 ( I Ks ) and Kcnj11 ( I KATP ). Conclusions This result together with downregulated HCN2 channels suggest that HCN channels might be an integral part of ventricular electric remodelling and might play a role in cardiac repolarization projected in altered arrhythmogenic profile of diabetic heart.
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Hadová et al. (2021) studied Diabetic cardiomyopathy (n=20). Streptozotocin vs. Citrate buffer was evaluated on HCN2 mRNA expression in left ventricles (p=<0.05). Streptozotocin-induced diabetes in rats reduced HCN2 mRNA expression by 60% and HCN2 protein expression by 70% exclusively in the ventricles.
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