Ca2+-permeable, outwardly-rectifying K+ channels in mesophyll cells of Arabidopsis thaliana
1998
Romano, L.A. | Miedema, H. | Assmann, S.M.
Arabidopsis thaliana has become a powerful tool in genetics and molecular biology. In order to use Arabidopsis as a model system for electrophysiological studies on plant cells, a detailed characterization of the transporters present in the plasma and vacuolar membranes of this species is required. We used the patch-clamp technique to study ion channels in the plasma membrane of Arabidopsis mesophyll cells. The most prominent conductance in these cells was a K+-selective, voltage-dependent, outwardly-rectifying channel (I(K.out)). In the whole-cell configuration, I(K.out) was observed in 100% of the cells assayed. In contrast, inward current was observed in less than 50% of the cells which were bathed in 100 mM K+, and was totally absent from cells bathed in 10 mM K+. The activation kinetics of I(K.out) were modulated by the external K+ concentration with a faster activation at low external K+. Tail-current analysis revealed that in addition to K+, I(K.out) is also permeable to Ca2+ and Ba2+. Externally applied Ba2+ also caused a voltage-dependent decrease in current magnitude, indicating that I(K.out) is also partially blocked by this classic K+ channel blocker. Single channels studied in outside-out patches showed Ca2+ and Ba2+ sensitivity, voltage dependence and time activation similar to that of I(K.out) in the whole-cell configuration. Given their permeability to Ca2+, these channels may function as an avenue for Ca2+ influx as well as K+ efflux, both of which may affect photosynthesis.
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