Investigating the action of ryanodine receptor on cycle length of action potential of the rabbit intact sinoatrial and atrioventricular nodes

Introduction: The role of ryanodine canal/receptor current on the pacemaker activity of heart cells is controversial. This study was performed to characterize the effects of ryanodine receptor (RyR), on the cycle length (CL) of action potential of the sinoatrial node (SAN) and the atrioventricular node (AVN) of rabbit heart. Materials and Methods: As a specific blocker of the RyR, the effects of 0.2 and 2 micromolar of Ryanodine on action potential CL was investigated. The action potential was recorded and measured from endothelial surface of intact SAN and AVN by two separated metal microelectrode before and after using ryanodine. The experimental method used, was intervention. Data analysis was performed using independent and paired T test Results: Inhibition of RyR by 0.2 and 2 M of Ryanodine prolonged CL by 11.6±4.3 and 30±6.75 % in SAN preparations and by 18.5 ± 6.3 and 65±11 % in AVN preparations. This effect was significantly (p< 0.05) longer on AVN than SAN. Conclusion: Rabbit SAN and AVN showed distinct different responses to the inhibition of RyR, which reflects the variation in contribution of this current to the pacemaker function of the cardiac nodes in the rabbit. As ryanodine did not cease pacemaker activity of any tissue preparation for two nodes therefore , it is possible to say that ryanodine receptor has no absolute role in generating action potential of nodes.