PURPOSE: Ionic currents in smooth muscle have fundamental roles in initiation and maintenance of excitability and contractile status. So we studied and characterized potassium ion channels in smooth muscle cells of rabbit seminal vesicle. MATERIALS AND METHODS: Single smooth muscle cells of New Zealand White rabbit seminal vesicle were obtained using proteolytic enzymes (collagenase and papain). Using single cell and channel recording methods of patch clamp, potassium channels in smooth muscle of seminal vesicle were recorded. RESULTS: Potassium currents recorded whole-cell patch clamp method were divided into maxi-K channel dominant cells (n=11) and the cells with mixture of maxi-K and delayed rectifier K channels (n=7). Inside-out mode of patch clamp technique was used to characterize the maxi-K channel. The channel showed outward rectification and Ca-dependency. The single channel conductance of this channel estimated from slope conductance was 188 pS in physiological condition. These characters were typical properties of maxi-K channel. CONCLUSIONS: From these results it is suggested that maxi-K channel was predominantly distributed in rabbit seminal vesicle cell. The physiological roles of this channel in modulating seminal vesicle smooth muscle tone need further studies.