Transient light-induced changes in ion channel and proton pump activities in the plasma membrane of tobacco mesophyll protoplasts

Rapid, transient changes of the membrane potential upon lighttransitions are generally observed in microelectrode studies.In a patch-clamp study similar responses to light transitionswere found in current clamp. Corresponding with the changesof membrane potential, light-induced current changes in voltageclamp were observed. This paper evaluates the involvement ofoutward rectifying conductances and plasma membrane bound H⁺-ATpases(proton pump) to these light responses in mesophyll protoplastsof Nicotiana tabacum L. The contribution of K⁺-channels to theseresponses, could be minimized by variation of the holding potentialor addition of the K⁺-channel blocker verapamil. It was concludedthat light transitions modulate both proton pump and K⁺-channelactivity. Effects of light on membrane current were not observedin root cells and chlorophyll-deficient cells, suggesting thatthe response requires photosynthetic activity. However, blockersof photosystems I and II did not affect current changes. Key words: Light, patch-clamp, plasma membrane, tobacco, whole cell