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  • Title: Characterization of SKT1, an inwardly rectifying potassium channel from potato, by heterologous expression in insect cells.
    Author: Zimmermann S, Talke I, Ehrhardt T, Nast G, Müller-Röber B.
    Journal: Plant Physiol; 1998 Mar; 116(3):879-90. PubMed ID: 9501121.
    Abstract:
    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 microM. An almost identical high Cs+ sensitivity (IC50 = 90 microM) 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.
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