Objective    To investigate the distribution of interstitial cells of Cajal (ICCs) —the pacemaker cells of the gut in the different parts of guinea pig pyeloureteral tract and explore the effect on the contraction of smooth muscle.     Methods    The ureteropelvic junction

upper ureteral

middle ureteral

lower ureteral tissues harvested from 10 guinea pigs were performed KIT immunofluorescent staining in stretched preparations. Smooth muscle strips of 2 mm×6 mm were dissected from the sites for tone determination. The frequency and amplitude of the smooth muscle were compared among different sites of pyeloureteral tract.     Results    Cells with positive staining by KIT and with similar morphology to ICCs were found in the entire pyeloureteral tract of guinea pigs. The density of ICCs-like cells in the ureteropelvic junction

upper ureteral

middle ureteral

and lower ureteral tissues were (5.20±0.98)

(3.90±0.98)

(3.03±0.98) and (2.50±0.81) respectively. The contraction of strips in different sites varied according to the distribution of ICCs. The amplitude and frequency of strips from the ureteropelvic junction and upper ureteral were significantly higher than those from middle ureteral and lower ureteral (P0.05). The contraction amplitude and frequency of strips were positively correlated with the number of ICCs (P0.05).     Conclusion    ICCs is unevenly distributed in the upper ureteral tract of guinea pig. The contraction amplitude and frequency of smooth muscle strips are correlated with the number of ICCs in different of sites of pyeloureteral tract.