Different distributions of interstitial cells of Cajal and platelet-derived growth factor receptor-α positive cells in colonic smooth muscle cell/interstitial cell of Cajal/platelet-derived growth factor receptor-α positive cell syncytium in mice

AIM To investigate the distribution and function of interstitial cells of Cajal (ICCs) and platelet-derived growth factor receptor-alpha positive (PDGFR alpha(+)) cells in the proximal and distal colon. METHODS The comparison of colonic transit in the proximal and distal ends was performed by colonic migrating motor complexes (CMMCs). The tension of the colonic smooth muscle was examined by smooth muscle spontaneous contractile experiments with both ends of the smooth muscle strip tied with a silk thread. Intracellular recordings were used to assess electrical field stimulation (EFS)induced inhibitory junction potentials (DP) on the colonic smooth muscle. Western blot analysis was used to examine the expression levels of ICCs and PDGFR alpha in the colonic smooth muscle. RESULTS Treatment with NG-nitro-L-arginine methyl ester hydrochloride (L-NAME) significantly increased the CMMC frequency and spontaneous contractions, especially in the proximal colon, while treatment with MRS2500 increased only distal CMMC activity and smooth muscle contractions. Both CMMCs and spontaneous contractions were markedly inhibited by NPPB, especially in the proximal colon. Accordingly, CyPPA sharply inhibited the distal contraction of both CMMCs and spontaneous contractions. Additionally, the amplitude of stimulation-induced nitric oxide (NO)/ICC-dependent slow DPs (sDPs) by intracellular recordings from the smooth muscles in the proximal colon was larger than that in the distal colon, while the amplitude of electric field stimulation-induced purinergic/PDGFR alpha-dependent fast DPs (fDPs) in the distal colon was larger than that in the proximal colon. Consistently, protein expression levels of c-Kit and anoctamin-1 (ANO1) in the proximal colon were much higher, while protein expression levels of PDGFR alpha and small conductance calcium-activated potassium channel 3 (SK3) in the distal colon were much higher. CONCLUSION The ICCs are mainly distributed in the proximal colon and there are more PDGFR alpha(+) cells are in the distal colon, which generates a pressure gradient between the two ends of the colon to propel the feces to the anus.