Immunosuppressants implicate protein phosphatase regulation of K+ channels in guard cells

Sheng Luan, Weiwei Li, Frank Rusnak, Sarah M. Assmann, Stuart L. Schreiber

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219 Scopus citations


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 languageEnglish (US)
Pages (from-to)2202-2206
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number6
StatePublished - Mar 15 1993

All Science Journal Classification (ASJC) codes

  • General


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