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.