Interstitial cells of Cajal (ICCs) are pacemaker cells that activate the periodic spontaneous depolarization (pacemaker potentials) responsible for the production of slow waves in gastrointestinal smooth muscle. Under current clamping, ICCs had a mean resting membrane potential of -58±3 mV and externally applied ET produced membrane depolarization in a dose-dependent manner. These effects were reduced by intracellular GDP beta S. A comparison of the concentration-dependent membrane depolarizations on pacemaker potentials to ET-1, ET-2 and ET-3 showed a rank order of potency ET-1≥ET-2≥ET-3 in cultured murine small intestinal ICCs. The pretreatment with Ca2+-free solution and thapsigargin, a Ca2+-ATPase inhibitor in endoplasmic reticulum, abolished the generation of pacemaker potentials and suppressed the ET-1 induced membrane depolarizations. Chelerythrine and calphostin C, protein kinase C inhibitors or naproxen, an inhibitor of cyclooxygenase, did not block the ET-1 induced effects on pacemaker potentials. Pretreatment with BQ-123 (ETA receptor antagonist) or BQ-788 (ETB receptor antagonist) blocked the ET-1 induced effects on pacemaker potentials in cultured murine small intestinal ICCs. However, pretreatment with BQ-788 selectively did not block the ET-1 induced effects on pacemaker potentials in cultured murine large intestinal ICCs. Also, only externally applied selective ETB receptor agonist, IRL 1620 did not show any influence on pacemaker potentials in cultured murine large intestine ICCs. RT-PCR results indicated the presence of the ETA and ETB receptor in ICCs. These results suggested that ET-1 modulates pacemaker potentials through ETA and ETB receptor activation in murine small intestinal ICCs and ETA receptor activation in murine large intestinal ICCs by external Ca2+ influx and internal Ca2+ release via protein kinase C or cyclooxygenase-independent mechanism. Therefore, the ICCs are targets for ET and their interaction can affect intestinal motility.