Morphology of mouse sinoatrial node and its expression of NF-160 and HCN4.

OBJECTIVE To explore the morphology and cell component of the sinoatrial node in adult mice and to observe the expressions of neurofilament protein (NF-160) and hyperpolarization-activated cyclic nucleotide regulation of cation channel 4 (HCN4) in sinus node cells. METHODS The right and left atria were collected from 10 adult mice. After paraffin embedding and serial section, these sections underwent Masson trichrome staining and NF-160 immunohistochemical staining, respectively, followed by observation under a light microscope. The right and left atria from another 5 mice were used for immunofluorescence staining using NF-160 and HCN4 antibodies, respectively, followed by observation under a confocal microscope. RESULTS The mouse sinoatrial node was close to the superior vena cava and below the epicardium. The shape of the mouse sinoatrial node was ovoid or irregular in the horizontal sections. We clearly saw a sinus node artery passing through the sinoatrial node, so the artery can be used as a location marker of the sinoatrial node. Immunofluorescence displayed the expression of NF-160 and HCN4 in both pacemaker cells and transitional cells of the sinoatrial node. Finally, sinoatrial node migrated along with Purkinje fibers of the right atrium. CONCLUSION The position of mouse sinoatrial node is more stable. The distal end of sinoatrial node extends to the right subendocardial layer and migrates with Purkinje fibers. In mouse sinoatrial node, both pacemaker cells and transitional cells are regularly distributed, and all have HCN4 and NF-160 expression.