Light-induced leaflet movement of Samanea samandepends on the regulation of membrane transporters in motor cells. Blue light (BL) stimulates leaflet opening by inducing K⁺release from the flexor motor cells. To elucidate the mechanism of K⁺-efflux (K_D)-channel regulation by light, flexor motor cell protoplasts were patch-clamped in a cell-attached configuration during varying illumination. Depolarization elicited outward currents through single open K_D channels. Changes in cell membrane potential (E _M) were estimated by applying voltage ramps and tracking the change of the apparent reversal 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 followed by darkness shifted E _M oppositely (i.e. hyperpolarized the cell). The BL-induced shifts ofE _M were not observed in cells pretreated with a hydrogen-pump inhibitor, suggesting a contribution by hydrogen-pump to the shift. BL also increased K_D-channel activity in a voltage-independent manner as 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 _@40increased by approximately 12 pS without a change of the single-channel conductance, possibly by increasing the probability of channel opening. Subsequent red-light and darkness reversed the change inG _@40. Thus, 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 an independent signaling pathway.

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