The interstitial cells of Cajal (ICC) as pacemaker cells of the gut contribute to rhythmic peristalsis and muscle excitability through initiation of slow wave activity that subsequently actively propagates into the musculature. An E-4031-sensitive potassium current makes a critical contribution to membrane potential in ICC. This study provides novel features of this current in ICC in physiological solutions and seeks to identify the channel isoform. In situ hybridization and KIT immunohistochemistry were combined to assess ERG mRNA expression in ICC in mouse jejunum, while the translated message was assessed by immunofluorescence co-localization of ERG and KIT proteins. E4031-sensitive currents in cultured ICC were studied by whole cell patch clamp using physiological potassium concentration in bath and pipette. M-erg1 and m-erg3 mRNA but not m-erg2 mRNA were detected in ICC by in situ hybridization combined with Kit immunohistochemistry. ERG3 protein was co-localized with KIT-immunoreactive ICC in jejunum sections, but ERG1 protein was visualized only in the smooth muscle cells. In physiological potassium, the E-4031-sensitive outward current in ICC was different from its counterpart in cardiac and gut smooth muscle cells. In particular, the inactivation upon depolarization and recovery from inactivation by hyperpolarization was modest in ICC. In summary, the E-4031-sensitive currents influence the kinetics of the pacemaker activity in ICC and contribute to the maintenance of the resting membrane potential in smooth muscle cells, which together constitutes a marked effect on tissue excitability. Whereas this current is mediated by ERG1 in smooth muscle, it is primarily mediated by ERG3 in ICC.