Objective    To investigate the potassium currents of the cardiac pacemaking cells induced and differentiated from rat mesenchymal stem cells (MSCs) modified by HCN4 gene.     Methods    Identified cardiac pacemaking cells were adopted as the experiment group

and the sinoatrial node cells of original infant rat cultured in the same period were regarded as the control group. Whole cell patch was used to measure the action potential of the pacemaking cells and sinoatrial node cells.     Results    Action potential of automatic depolarization at dilatation was recorded in both the differentiated cardiac pacemaking cells and sinoatrial node cells. There was no significant difference on amplitudes of resting potential

amplitudes and cycle of action potential [(-50±2.8) vs (-55±5.5)，(-60±2.5) vs (-65±2.5)，(240±57) ms vs (250±60) ms]

but the field potential was much lower in cardiac pacemaking cells than the control group[(-30±2.5) vs (-55±55)，P0.01].     Conclusion    Whole cell patch technology can record the action potential of automatic depolarization at dilatation in the cardiac pacemaking cells

with the similar characteristics of the sinoatrial node cells of infant rat cultured originally.