A LOW-THRESHOLD SUSTAINED INWARD CURRENT ACTIVATED AT THE DIASTOLIC POTENTIAL RANGE IN RABBIT SINOATRIAL NODE CELLS

The whole-cell voltage clamp was performed in myocytes dissociated from the rabbit sinoatrial node using the collagenase method. After blocking both the hyperpolarization-activated current and the membrane K+ conductance, depolarizations from -80 mV to values in the range -70 to -50 mV induced a sustained current. This low-threshold sustained inward current was blocked by both organic and inorganic Ca2+ channel blockers, but tetrodotoxin 30 mu M was ineffective. Isoprenaline increased this current. It is suggested that this current plays an important role in driving the diastolic depolarization.