Résumé
Objective: We have investigated the properties of the hyperpolarization-activated (If) current in pacemaker cells from the mouse sino-atrial node (SAN). Methods: The If current was studied in cells isolated enzymatically from the SAN region of adult C57BL6/J mice. The whole-cell variation of the patch-clamp technique was employed to investigate the basic properties of If. Results: In mouse SAN cells, the If current density at −120 mV was 18±2 pA/pF (n=23). If was not detected in cells showing atrial-like morphology that were also found in SAN preparations (n=7). If was blocked by 5 mM Cs+, was inhibited by application of 5 μM acetylcholine, and was increased by 10 μM noradrenaline. The If current reversal potential was −31±2 mV under physiological concentration of Na+ and K+ ions. Lowering the extracellular Na+ concentration reduced If amplitude, while increased when the extracellular K+ concentration was augmented. If voltage for half activation was −87±1 mV (n=6). Conclusions: We conclude that the native If current in mouse SAN cells shows functional properties that are similar to If described in rabbit SAN tissue. This study opens the possibility of investigating the involvement of If in the regulation of heart rate in genetically modified mice.