Isolated downregulation of HCN2 in ventricles of rats with streptozotocin-induced diabetic cardiomyopathy

Abstract

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 (Ito1), Kcnh2 (IKr), Kcnq1 (IKs) and Kcnj11 (IKATP). 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.

Rapid changes of mRNA expressions of cardiac ion channels affected by Torsadogenic drugs influence susceptibility of rat hearts to arrhythmias induced by Beta‐Adrenergic stimulation

“…To prove the quality of the isolated RNA, electrophoresis in 2% of agarose gel (Agarose, Sigma‐ Aldrich) was carried out and subsequently reverse transcription was performed on intact RNA samples (High capacity cDNA Reverse Transcription Kit with RNAse inhibitors; Applied Biosystems). Expressions of selected cardiac genes (see Table 1) were evaluated by quantitative PCR (RT‐qPCR) using the SYBR™ Select Master Mix (Thermo Fisher Scientific) on a StepOnePlus™ Real‐Time PCR System (Thermo Fisher Scientific), as described previously 28–30 . The primers for qPCR were designed by Primer‐BLAST 31 .…”

“…There is only one variant -rat ERG encoded by Kcnh2 expressed in the rat heart. 28 There is also evidence that I Kr blockers do not affect this current in rats 51 and that they do not affect the action potential in small rodents. 35 Labelling of the groups: CLA, clarithromycin-treated rats; CLA + FUR, furosemide and clarithromycin-treated rats; CON, controls; FUR, furosemide-treated rats.…”

Effects of Electrical Remodeling on Atrial Fibrillation in Diabetes Mellitus

“…The reduction of HCN isoforms were also reduced in the sinoatrial node of diabetic rats induced with STZ injection, indicating HCN might be an important contributor to the dysfunction of sinoatrial node in DM [38]. mRNA and protein expressions of hyperpolarizationactivated cyclic nucleotide-gated channel 2 (HCN2) were reduced exclusively in the ventricles of STZ rats [39]. However, HCN2 expression in the atrium of STZ rats and H9c2 cells treated with high glucose were unchanged.…”

Functional Regulation of KATP Channels and Mutant Insight Into Clinical Therapeutic Strategies in Cardiovascular Diseases

“…Highly specific HCN 2 (hyperpolarization-activated, cyclic-nucleotide gated channels 2) in ventricular myocytes, an integral part of ventricular electric remodeling, and the reduced expression of its mRNA, leads to the downregulation of the K ATP channel current, which is one of the partial causes of arrhythmia in diabetic rats ( Hadova et al, 2021 ; White et al, 2021 ). Exogenous cholesterol eliminated the increase in SUR2, suggesting that cholesterol may regulate K ATP channel expression and explain why patients with hypercholesterolemia were also able to cope with ischemic events ( Geiger et al, 2021 ).…”