Characterization of spontaneous contractions of circular muscle strips isolated from rat proximal colon. A: Representative traces showing spontaneous mechanical activities of mucosa-free circular muscles. An arrow indicates the initial tension applied after mounting tissues. Arrowheads in each trace indicate at time = 45 min. Calculation method of peak amplitude, peak time, FWHM value were shown in the high-magnification view. B-E: Average of contraction frequency (B), peak amplitude (C), FWHM (D), and peak time (E) were determined in the presence or absence (None) of indomethacin (IND, 10 μM), tetrodotoxin (TTX, 1 μM), and/or L-NAME (0.1 mM). *P < 0.05 vs. None group by ANOVA followed by Dunnett's multiple comparison test. No significant difference was detected in amplitude or FWHM. (N = 6 - 25)