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 light transitions are generally observed in microelectrode studies, In a patch-clamp study similar responses to light transitions were found in current clamp, Corresponding with the changes of membrane potential, light-induced current changes in voltage clamp were observed, This paper evaluates the involvement of outward rectifying conductances and plasma membrane bound H+-ATPases (proton pump) to these light responses in mesophyll protoplasts of Nicotiana tabacum L. The contribution of K+-channels to these responses, could be minimized by variation of the holding potential or addition of the K+-channel blocker verapamil, It was concluded that light transitions modulate both proton pump and K+-channel activity, Effects of light on membrane current were not observed in root cells and chlorophyll-deficient cells, suggesting that the response requires photosynthetic activity, However, blockers of photosystems and II did not affect current changes.