Long-term treatment with ivabradine in post-myocardial infarcted rats counteracts f-channel overexpression

BACKGROUND AND PURPOSE Recent clinical data suggest beneficial effects of ivabradine, a specific heart rate (HR)-lowering drug, in heart failure patients. However, the mechanisms responsible for these effects have not been completely clarified. Thus, we investigated functional/molecular changes in I _f, the specific target of ivabradine, in the failing atrial and ventricular myocytes where this current is up-regulated as a consequence of maladaptive remodelling. EXPERIMENTAL APPROACH We investigated the effects of ivabradine (IVA; 10 mg·kg ^-1·day ^-1 for 90 days) on electrophysiological remodelling in left atrial (LA), left ventricular (LV) and right ventricular (RV) myocytes from post-mycardial infarcted (MI) rats, with sham-operated (sham or sham + IVA) rats as controls. I _f current was measured by patch-clamp; hyperpolarization-activated cyclic nucleotide-gated (HCN) channel isoforms and microRNA (miRNA-1 and miR-133) expression were evaluated by reverse transcription quantitative PCR. KEY RESULTS Maximal specific conductance of I _f was increased in MI, versus sham, in LV (P < 0.01) and LA myocytes (P < 0.05). Ivabradine reduced HR in both MI and sham rats (P < 0.05). In MI + IVA, I _f overexpression was attenuated and HCN4 transcription reduced by 66% and 54% in LV and RV tissue, respectively, versus MI rats (all P < 0.05). miR-1 and miR-133, which modulate post-transcriptional expression of HCN2 and HCN4 genes, were significantly increased in myocytes from MI + IVA. CONCLUSION AND IMPLICATION The beneficial effects of ivabradine may be due to the reversal of electrophysiological cardiac remodelling in post-MI rats by reduction of functional overexpression of HCN channels. This is attributable to transcriptional and post-transcriptional mechanisms.