Blue light activates potassium-efflux channels in flexor cells from Samanea saman motor organs via two mechanisms

Light induced leaflet movement of Samanea saman depends on the regulation o f membrane transporters in motor cells. Blue light (BL) stimulates leaflet opening by inducing K+ release from the flexor motor cells. To elucidate th e mechanism of K+-efflux (K-D)-channel regulation by light, flexor motor ce ll protoplasts were patch-clamped in a cell-attached configuration during v arying illumination. Depolarization elicited outward currents through singl e open K-D channels. Changes in cell membrane potential (E-M) were estimate d by applying voltage ramps and tracking the change of the apparent reversa l potential of K-D-channel current. BL shifted E-M in a positive direction (i.e. depolarized the cell) by about 10 mV. Subsequent red light pulse foll owed by darkness shifted E-M oppositely (i.e. hyperpolarized the cell). The BL-induced shifts of E-M were not observed in cells pretreated with a hydr ogen-pump inhibitor, suggesting a contribution by hydrogen-pump to the shif t. BL also increased K-D-channel activity in a voltage-independent manner a s reflected in the increase of the mean net steady-state patch conductance at a depolarization of 40 mV relative to the apparent reversal potential (G (@40)). G(@40) increased by approximately 12 pS without a change of the sin gle-channel conductance, possibly by increasing the probability of channel opening. Subsequent red-light and darkness reversed the change in G(@40). T hus, K+ efflux, a determining factor for the cell-volume decrease of flexor cells, is regulated by BL in a dual manner via membrane potential and by a n independent signaling pathway.