The present study was aimed at elucidating how pacemaker activity (plateau potentials) (mean frequency: 15.9 +/- 2.8 times min(-1)) from submucosal interstitial cells of Cajal (ICC-SM) control spontaneous contractions in the mouse proximal colon. Mechanical activities in the circular muscle direction showed high-frequency (mean frequency: 15.6 +/- 2.7 times min(-1)) and low-amplitude (mean amplitude: 0.01 +/- 0.005 g) (HFLA) rhythmic contractions. Simultaneous recordings of circular muscle mechanical activity and electrical activity from ICC-SM revealed that HFLA contractions were synchronized with plateau potentials (mean frequency: 15.9 +/- 2.8 times min(-1)). Although low-frequency (3.5 +/- 2.1 times min(-1)) and high-amplitude (0.12 +/- 0.03 g) (LFHA) contractions in both longitudinal and circular muscle directions were synchronized with burst of action potentials in both muscle cells, these LFHA contractions were not synchronous with plateau potentials. Intracellular Ca2+ release from the internal stores through IP3 receptors is not a major factor to generate both action potentials differently from plateau potentials. Neither tetrodotoxin nor atropine affected the plateau potentials. The results reveal that the pacemaker activity from ICC-SM drives only the spontaneous HFLA (one-tenth amplitude of the LFHA circular and longitudinal muscle contractions) circular muscle contractions without control by enteric nerves.