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Arginine (Arg), as a basic amino acid, has been reported to be involved in regulation of gut motility. However, the evidence is limited and the underlying mechanism is not fully understood. Our study was conducted to investigate the effects of L-Arg on spontaneous contraction of the longitudinal muscle strip (LMS) of the rat colon and the relevant mechanisms. An organ bath system was used to detect the contractile force of the LMS. Whole-cell voltage-clamp techniques were applied to observe alterations in the currents of large conductance Ca2+-activated K+ (KCa) channels, voltage-dependent potassium (KV) channels, and L-type Ca2+ channels (LTCCs) in smooth muscle cells (SMCs) of the colon. We found that L-Arg within the physiological concentration had no effect on contraction of LMS, while 1 mM L-Arg significantly increased both the amplitude and frequency of LMS contractility. And the increase in force was mucosa-dependent, whereas changes in frequency as well as in amplitude were inhibited by atropine. In addition, L-Arg (1 mM) activated the LTTCs and inhibited both KCa channels and KV channels on SMCs. Thus, L-Arg above the physiological concentration exerted an excitatory effect on colonic LM contraction, and stimulation by L-Arg was mediated by ACh. In addition, LTCCs, KCa channels, and KV channels on SMCs were involved in the action of L-Arg. [ABSTRACT FROM AUTHOR]