In order to determine whether the K+ channel openers (PCOs), which are suggested to open K+ channels and to relax bronchial smooth muscle, would directly activate voltage-dependent K+ channels, single channel currents were studied on cell-attached and inside-out patches of smooth muscle acutely dissociated from bronchi of guinea-pig. The resting membrane potentials measured in whole-cell recording configuration showed no difference with control when cromakalim and lemakalim were applied extracellularly, which, however increased the conductance values of K+ channels with depolarization from 75.2 +/- 5.1 pS to 85.9 +/- 11.8 pS and 82.1 +/- 5.5 pS, respectively. The channels kinetics were also affected by PCOs. Mean open time (tau o) and open probability increased, in which the effects of lemakalim was stronger than that of cromakalim. Both PCOs elicited the multichannel activities in some patches. It is suggested that PCOs could evoke K+ channels with depolarization and stimulate K+ efflux, which may affect the excitability of muscle cells.