Razi Journal of Medical Sciences

    Background & Aim: The role of ryanodine receptor(RYR) on pacemaker activity of heart cells is controversial. Some investigators have suggested that it is obligatory, while others believe it is partial and not obligatory. The principle aim of this study was once more to characterize the role of ryanodine receptor(RyR) on the pacemaker activity of the sinoatrial node(SAN) and the atrioventricular node(AVN) in the mouse. Material and Methods: In an experimental study the effect of ryanodine on the cycle length(CL) of action potential of the intact SAN and the AVN of the heart mouse was assessed. The recording of action potential was extra cellular and was done by 2 separated metal microelectrodes. Paired and independent t tests were carried on accordingly. If the P values were less than 0.05, the differences were considered significantly. Results: Ryanodine with 0.2 and 2µM concentrations prolonged CL of action potential by 46.50±15.75% and 70±21% in SAN preparations while 163±72.25% and 241±91.25% in AVN preparations. During ryanodine use, the pacemaker activity was not stopped for all preparations. The effect of ryanodine on two nodes was significant with respect to control. Conclusion: On the basis of obtained result, it may be said that the ryanodine receptor current exists in SAN & VAN. AVN the pacemaker activity was functioning continuously in cardiac nodes when ryanodine was used, therefore, the role of RyR for pacemaker activity is not obligatory. The effect of ryanodine on AVN is significantly greater than SAN that is, the role of RyR in two nodes is not similar.