Characterization of the effects of Ryanodine, TTX, E-4031 and 4-AP on the sinoatrial and atrioventricular nodes

Aims: To characterize the effects of inhibition of Ryanodine receptor (RyR), TTX-sensitive neuronal Na+ current (i(Na)), rapidly activating delayed rectifier K+ current (i(Kr)) and ultrarapid delayed rectifier potassium current (I-Kur) on the pacemaker activity of the sinoatrial node (SAN) and the atrioventricular node (AVN) in the mouse. Methods: The structure of mouse AVN was studied by histology and immunolabelling of Cx43 and hyperpolarization-activated, cyclic nucleotide-binding channels (HCN). The effects of Ryanodine, TTX, E-4031 and 4-AP on pacemaker activities recorded from mouse intact SAN and AVN preparations have been investigated. Results: Immuno-histological characterization delineated the structure of the AVN showing the similar molecular phenotype of the SAN. The effects of these inhibitors on the cycle length (CL) of the spontaneous pacemaker activity of the SAN and the AVN were characterized. Inhibition of RyR by 0.2 and 2 mu M Ryanodine prolonged CL by 42 +/- 12.3% and 64 +/- 18.1% in SAN preparations by 163 +/- 72.3% and 241 +/- 91.2% in AVN preparations. Inhibition of TTX-sensitive i(Na) by 100 nM TTX prolonged CL by 22 +/- 6.0% in SAN preparations and 53 +/- 13.6% in the AVN preparations. Block of i(Kr) by E-4031 prolonged CL by 68 +/- 12.5% in SAN preparations and 28 +/- 3.4% in AVN preparations. Inhibition of i(Kr) by 50 mu M 4-AP prolonged CL by 20 +/- 3.4% in SAN preparations and 18 +/- 3.0% in AVN preparations. Conclusion: Mouse SAN and AVN showed distinct different response to the inhibition of RyR, TTX-sensitive I-Na, I-Kr and i(Kur). which reflects the variation in contribution of these currents to the pacemaker function of the cardiac nodes in the mouse. Our data provide valuable information for developing virtual tissue models of mouse SAN and AVN. (C) 2007 Published by Elsevier Ltd.