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Phosphatase antagonist okadaic acid inhibits steady‐state K + currents in guard cells of Vicia faba
Author(s) -
Thiel Gerhard,
Blatt Michael R.
Publication year - 1994
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/j.1365-313x.1994.00727.x
Subject(s) - okadaic acid , phosphatase , depolarization , chemistry , biophysics , dephosphorylation , conductance , acid phosphatase , patch clamp , voltage clamp , membrane potential , guard cell , biochemistry , phosphorylation , biology , enzyme , receptor , physics , condensed matter physics
Summary The effects of protein phosphatase inhibitors on steady‐state K + currents in the plasma membrane of Vicia faba guard cells were studied. Cells were impaled with double barrelled electrodes to monitor membrane voltage and K + currents under voltage clamp. Okadaic acid (OA) (1 μM), a specific inhibitor of phosphatase 1 and 2A activity, blocks inward ( l K + (in) ) and outward ( l K + (out) ) rectifying K + channels. Both currents decreased in parallel with a sigmoidal time course with 50% inhibition at about 8 min. With 0.2 μM OA inhibition became slower and more variable (4–34 min). Inhibition did not recover by washing cells ≤ 20 min in OA‐free solution. In five out of seven cells OA also induced a rise in the background conductance, which lagged behind the inhibition of K + current. Both decaying l K * (out) and rising leak conductance caused a depolarization. OA‐induced inhibition of l K + (in) and l K + (out) was without a significant effect on the kinetics of voltage‐dependent current activation and deactivation. In an alternative approach, guard cells were loaded from the voltage recording pipette with the non‐specific phosphatase inhibitor naphthylphosphate. After an impalement of some minutes l K + (in) and l K + (out) were small or undetectable. In conclusion inward and outward K + channels in guard cells have a common voltage‐independent mode of control which is sensitive to phosphatase inhibitors. The known specificity of OA points to a mode of action in which a net increase of protein phosphorylation through inhibition of phosphatase 1 and/or 2A activity blocks conductance of both, l K + (in) and l (out)