The elevation of Ca2+ levels in the cytoplasm inactivates inward-rectifying K+ channels that play a central role in regulating the apertures of stomatal pores in higher plants. However, the mechanism for the Ca2+-mediated inhibition of K+-channel function is unknown. Using patch-clamp techniques, we show that cyclophilin-cyclosporin A and FK506-binding protein-FK506 complexes, which are highly specific inhibitors of protein phosphatase 2B (calcineurin), block Ca2+-induced inactivation of K+ channels in Vicia faba guard cells. A constitutively active calcineurin fragment that is Ca2+-independent inhibits K+-channel activity in the absence of Ca2+. We have also identified an endogenous Ca2+-dependent phosphatase activity from V. faba that is inhibited by the cyclophilin-cyclosporin A and FK506-binding protein-FK506 complexes. Our findings implicate a Ca2+-dependent, calcineurin-like protein phosphatase in a Ca2+ signal-transduction pathway of higher plants.
|Original language||English (US)|
|Number of pages||5|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|State||Published - Mar 15 1993|
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