Quantitative Head-to-Tail Analysis Reveals Heterogeneous Cellular Organization and Connexin Expression in the Porcine Sinoatrial Node

Porcine sinoatrial node head-to-tail mapping shows >9-fold higher pacemaking cardiomyocyte density than a prior cross-species estimate, with region-specific connexin and HCN4 expression.

• Why it matters: Functional differences between leading pacemaking sites lack a resolved structural mechanism linking intra- and inter-tissue current source–sink relationships in the SAN.
• What they did: Porcine SAN longitudinal cryosections were immunostained and quantitatively analyzed for pacemaking cardiomyocyte density, cell organization, and connexin isoform (CX40, CX43, CX45) plus HCN4 expression across head, mid, and tail regions.
• The result: The head had large PCM clusters, low fibroblast density, highest HCN4, and lowest CX40/CX43; the tail had smaller clusters, lower HCN4, and higher CX40/CX43/CX45; the mid showed aligned clusters and highest CX40/CX45, supporting distinct intra- and inter-tissue coupling patterns.

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