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Plant and Cell Physiology, 1998, Vol. 39, No. 6 600-606
© 1998

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

Stephan Brandt and Joachim Fisahn1

Max Planck Institut für molekulare Pflanzenphysiologie Karl Liebknechtstr. 25, 14476 Golm, Germany

1 To whom correspondence should be addressed.

Poly(A)+ mRNA was isolated from leaves of potato plants (Solatium 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 H20 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 BaCl2. 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.

(Received November 7, 1997; Accepted March 21, 1998)
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