抄録
The sinoatrial (SA) node is a complex and heterogeneous tissue in terms of electrical activity: its pacemaker activity, shape of the action potential and conduction velocity vary between the center and periphery of the SA node. The aim of this study was to investigate regional heterogeneity of ion channel mRNA expression in the rabbit SA node and its surrounding atrial muscle. Small tissue samples (1.5x1.5x0.5 mm) including the center or the periphery of the SA node (C-SAN or P-SAN) as well as the right atrial appendage (RA) were dissected from the rabbit heart and mRNAs of various ion channel subunits were evaluated using a quantitative real-time PCR method. There were progressive increases in the expression of HCN1, HCN4 and Cav1.3 mRNAs from the RA to the center of the SA node (RA<P-SAN<C-SAN). In contrast, Cav1.2, Kv1.4, connexin43 and ryanodine receptor mRNAs were less abundant in the SA node than in the RA. There was no significant difference in sarcolemmal Na/K pump and connexin45 mRNAs among the three sites. These observations may provide a molecular basis for understanding the sophisticated structural and functional organization of the SA node as a dependable pacemaker of the heart. [Jpn J Physiol 54 Suppl:S107 (2004)]
