Pacemaker activity from submucosal interstitial cells of Cajal drives high‐frequency and low‐amplitude circular muscle contractions in the mouse proximal colon

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Abstract
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.