Properties of the hyperpolarization-activated current (If) in isolated mouse sino-atrial cells

Abstract

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