Pacemaker activity of the sinoatrial node has been studied extensively in various animal species, but is virtually unexplored in man. As such, it is unknown whether the fast sodium current (I(Na)) plays a role in the pacemaker activity of the human sinoatrial node. Recently, we had the unique opportunity to perform patch-clamp experiments on single pacemaker cells isolated from a human sinoatrial node. In 2 out of the 3 cells measured, we observed large inward currents with characteristics of I(Na). Although we were unable to analyze the current in detail, our findings provide strong evidence that I(Na) is present in human sinoatrial node pacemaker cells, and that this I(Na) is functionally available at potentials negative to -60 mV.
Keywords: action potentials; humans; ion channels; sinoatrial node; sodium channels.