Acute direct effects of cyclosporine on extracellular field potential of isolated rabbit AV node during experimental atrial fibrillation

Introduction: Previous studies have indicated a relationship between MPTP pore and AV nodal rate-dependent properties. The aim of present study was to determine acute direct effects of cyclosporine on extracellular field potential of isolated rabbit AV node during experimental atrial fibrillation. Methods: In one group of male New Zealand rabbits (1.5-2.5 kg) cumulative concentrations of cyclosporine (0.5 – 10 m) were applied on isolated perfused atrio-nodal preparation (n=7). Extracellular field potential recording was sampled during specific stimulation protocols (recovery, zone of concealment and atrial fibrillation) in the presence of drug on electrophysiological properties of AV-node. Results: Cyclosporine significantly decreased the ventricular rate (HH mean) from 231.8 ± 5.7 to 277.4 ± 14.6 msec and functional refractory period during AF (AF FRP) from 138.3 ± 7.5 to 161.2 ± 10.31 msec in control and treated groups, respectively. Effective refractory period during AF (AF ERP) was significantly decreased by cyclosporine 10 mM compared to control group (p<0.05). Conclusion: Cyclosporine-evoked slowing ventricular heart rate during AF was induced by increasing functional refractoy period and ZOC. A possible mechanism can be through blocking of MPT pores.