Ether a-go-go related gene (ERG) K channels have been implicated in the generation of pacemaker activities in the heart. To study the presence and function of ERG K channels in the pacemaker cells of the small intestine (the interstitial cells of Cajal, ICC), a combination of the patch clamp technique, tissue and live cell immunohistochemistry, RT-PCR and in vitro functional studies were performed. Nonenzymatically isolated ICC in culture were identified by vital staining and presence of rhythmic inward currents. RT-PCR showed presence of ERG mRNA in the intestinal musculature and immunohistochemistry on tissue and cultured cells demonstrated that HERG-like protein was concentrated on ICC in the Auerbach's plexus region with scattered positivity in smooth muscle cells. Whole cell ERG K⁺ currents were evoked upon hyperpolarization from 0 mV (but not from -70 mV) up to -120 mV and showed strong inward rectification. The currents were inhibited by E-4031, cisapride, La³⁺ and Gd³⁺. The ERG K⁺ inward current had a typical transient component with very fast activation and inactivation kinetics followed by significant steady state current. The ERG K⁺ current was insensitive to barium up to 50 µM. E-4031 also inhibited TEA insensitive outward current indicating that the ERG K⁺ current is operating at depolarizing potentials. In contrast to TEA, blockers of the ERG K⁺ currents caused marked increase in tissue excitability as reflected by an increase in slow wave duration and an increase in superimposed action potential activity. Effects of 4-AP were minor in comparison with E4031. In summary, ERG K channels in ICC contribute to the membrane potential and play a role in the regulation of pacemaker activity of the small intestine.