Caratterizzazione molecolare e funzionale del canale HCN4 nel nodo senoatriale di coniglio

Molecular and functional characterisation of the HCN4 channel in rabbit sinoatrial node The cardiac sinoatrial node (SAN) is composed of specialised myocytes that generate the spontaneous electrical activity responsible for the cardiac rhythm. This automaticity relies on the spontaneous slow depolarization (pacemaker potential), which at the end of an action potential drives the membrane potential to the threshold for a new event. The most important contribution to the net inward current flowing during this pacemaker potential comes from the activation of the If current. We characterised the principal f channels molecular constituent, HCN4 (Hyperpolarization-activated Cyclic Nucleotide-gated) channel, identified as the most important in the rabbit SAN. In the present work, we used immunofluorescence and western blot analysis to reveal the expression of HCN4 protein and in situ hybridisation to reveal the expression of HCN4 mRNA. There was a strong correlation between HCN4 mRNA and protein expression in the intercaval region, the same region from which pacemaker activity can be recorded. We also delineated the HCN4 distribution in the entire tissue and, with gene silencing experiments, we demonstrated that this isoform is functionally the major constituent of the pacemaker channel. In conclusion, this work shows that HCN4 is a specific marker of the natural cardiac pacemaker, interesting and important result in perspective to realising a biological pacemaker.