Identification of a K^+ Channel from Potato Leaves by Functional Expression in Xenopus Oocytes

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Poly(A)^+ mRNA was isolated from leaves of potato plants (Solanum tuberosum L.cv.Desiree) according to standard protocols. This poly(A)^+ mRNA was injected via glass microcapillaries into oocytes that were surgically removed from the African clawed toad Xenopus laevis. As a control, oocytes were either injected with H_2O or remained untreated. Three days after injection the oocytes were analyzed by two electrode voltage clamping. Current voltage analysis revealed that a K^+ channel from potato was functionally expressed in injected oocytes. The identity of this K^+ channel was confirmed by its substrate specificity and a shift in the reversal potential. In particular, when the outside K^+ concentration was increased the reversal potential of poly(A)^+ injected oocytes shifted to more positive values. Furthermore, K^+ outward currents declined when the outside K^+ concentration was raised from 0.1 to 100 mM. Inward currents increased with an elevation of the K^+ concentration. Several pharmaceuticals were tested for their potential to block this K^+ channel. As a result, the channel was completely blocked by BaCl_2. A three state reaction kinetic model was used to simulate the currents through the K^+ transport protein as function of the extracellular K^+ concentration. In particular, the simulation revealed current voltage relations that exactly matched the measured ones. Saturation of current voltage curves emerged from the simulation as a consequence of high extracellular potassium concentration.
日本植物生理学会の論文

Identification of a K^+ Channel from Potato Leaves by Functional Expression in Xenopus Oocytes

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