AIM: To investigate the effects of in vivo application of L - arginine on potassium channels in bronchial smooth muscle cells (BSMC) isolated from asthmatic model rats.METHODS: Male SD rats were randomly divided into control group,asdimatic group and asthmatic rats treated with L-arginine (L-Arg group). Single BSMCs were obtained by acute enzyme separation method. The resting membrane potential (Em), Ca2+ - activated K+ channels (BKca) currents and voltage - dependent K+ channel (Kv) currents in BSMCs were recorded under whole - cell patch clamp technique. RESULTS: (1) The Em of asthmatic group was significantly lower than that in control group ( P 0.05) . (2) The peak current density at + 50 mV of Kca: IKca in asthmatic group [ (43.8?16.5) pA/pF] was significandy lower than that in normal group [ (72.5?19.9) pA/pF] ( P