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Characterization of SKT1, an Inwardly Rectifying Potassium
Channel from Potato, by Heterologous Expression in Insect Cells
Sabine Zimmermann1,
Ina Talke1,
Thomas Ehrhardt,
Gabriele Nast2, and
Bernd Müller-Röber*
Max-Planck-Institut für Molekulare Pflanzenphysiologie,
Karl-Liebknecht-Strasse 25, Haus 20, D-14476 Golm/Potsdam,
Germany
A cDNA
encoding a novel, inwardly rectifying K+
(K+in) channel protein, SKT1, was cloned from
potato (Solanum tuberosum L.). SKT1 is related to
members of the AKT family of K+in channels
previously identified in Arabidopsis thaliana and potato. Skt1 mRNA is most strongly expressed in leaf
epidermal fragments and in roots. In electrophysiological, whole-cell,
patch-clamp measurements performed on baculovirus-infected insect
(Spodoptera frugiperda) cells, SKT1 was identified as a
K+in channel that activates with slow kinetics
by hyperpolarizing voltage pulses to more negative potentials than  60
mV. The pharmacological inhibitor Cs+, when applied
externally, inhibited SKT1-mediated K+in
currents half-maximally with an inhibitor concentration
(IC50) of 105 µm. An almost identical high
Cs+ sensitivity (IC50 = 90 µm) was found for the potato guard-cell K+in channel KST1 after expression in insect
cells. SKT1 currents were reversibly activated by a shift in external
pH from 6.6 to 5.5, which indicates a physiological role for
pH-dependent regulation of AKT-type K+in
channels. Comparative studies revealed generally higher current amplitudes for KST1-expressing cells than for SKT1-expressing insect
cells, which correlated with a higher targeting efficiency of the KST1
protein to the insect cell's plasma membrane, as demonstrated by
fusions to green fluorescence protein.
1
These authors contributed equally to this
paper.
2
Present address: PlantTec Biotechnologie GmbH,
Forschung & Entwicklung, Hermannswerder 14, D-14473 Potsdam, Germany.
*
Corresponding author; e-mail mueller{at}mpimp-golm.mpg.de; fax
49-311-977-2301.
Plant Physiol. (1998) 116: 879-890
Copyright Clearance Center: 0032-0889/98/116/0879/12
© 1998 American Society of Plant Physiologists
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