Use‐dependent inhibition of hHCN4 by ivabradine and relationship with reduction in pacemaker activity

• Published in: British journal of pharmacology 2007-01, Vol.150 (1), p.37-46
• Main Authors: Thollon, C, Bedut, S, Villeneuve, N, Cogé, F, Piffard, L, Guillaumin, J‐P, Brunel‐Jacquemin, C, Chomarat, P, Boutin, J‐A, Peglion, J‐L, Vilaine, J‐P
• Format: Article
• Language: English
• Subjects: Action Potentials - drug effects; Animals; Benzazepines - pharmacology; Biological and medical sciences; Biological Clocks - drug effects; CHO Cells; Cricetinae; Cricetulus; Cyclic Nucleotide-Gated Cation Channels; Female; Heart Rate - drug effects; human HCN4 channel; Humans; Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; Ion Channels - antagonists & inhibitors; Ion Channels - genetics; ivabradine; Male; Medical sciences; Muscle Proteins - antagonists & inhibitors; Muscle Proteins - genetics; pacemaker; patch‐clamp; Pharmacology. Drug treatments; Potassium Channels; Rabbits; Rats; Rats, Wistar; Research Papers; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger - genetics; RT–PCR; S 16257; sino‐atrial action potentials; Swine
• ISSN: 0007-1188; 1476-5381
• DOI: 10.1038/sj.bjp.0706940

Background and purpose: Ivabradine, a specific and use‐dependent I f inhibitor, exerts anti‐ischaemic activity purely by reducing heart rate. The aim of this work was to characterize its effect on the predominant HCN channel isoform expressed in human sino‐atrial nodes (hSAN), to determine its kinetics in HCN channels from multicellular preparations and rate‐dependency of its action. Experimental approach: RT‐PCR analysis of the four HCN channel isoforms was carried out on RNAs from hSAN. Patch‐clamp and intracellular recordings were obtained from CHO cells stably expressing hHCN4 and isolated SAN, respectively. Beating rate of rat isolated atria was followed using a transducer. Key results: hHCN4 mRNAs were predominant in hSAN. Ivabradine induced a time‐dependent inhibition of hHCN4 with an IC50 of 0.5 μM. In rabbit SAN, ivabradine progressively reduced the frequency of action potentials: by 10% after 3 h at 0.1 μM, by 14% after 2 h at 0.3 μM and by 17% after 1.5 h at 1 μM. After 3h, ivabradine reduced the beating rate of rat right atria with an IC30 of 0.2 μM. The onset of action of ivabradine was use‐dependent rather than time‐dependent with slower effects than caesium, an extracellular I f blocker. Ivabradine 3 μM decreased the frequency of action potentials in SAN from guinea‐pig, rabbit and pig by 33%, 21% and 15% at 40 min, respectively. Conclusions and implications: The use‐dependent inhibition of hHCN4 current by ivabradine probably contributes to its slow developing effect in isolated SAN and right atria and to its increased effectiveness in species with rapid SAN activity. British Journal of Pharmacology (2007) 150, 37–46. doi:10.1038/sj.bjp.0706940