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Published on December 3, 2008; 10.1104/pp.108.129007

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Received September 1, 2008
Accepted November 24, 2008

Phosphatidylinositol (4,5)-bisphosphate inhibits K+-efflux channel activity in NT1 tobacco cultured cellsTobacco Cultured Cells

Xiaohong Ma , Oded Shor , Sofia Diminstein , Ling Yu , Yang Ju Im , Imara Perera , Aaron Lomax , Wendy F. Boss , and Nava Moran *

The Robert H. Smith Institute for Plant Sciences and Genetics in Agriculture, Faculty of Agricultural, Food and Environmental Quality Sciences, the Hebrew University of Jerusalem, Rehovot 76100, Israel; Dept. Plant Biology, North Carolina State University, Raleigh, NC 27695-7649, USA

* Corresponding author; email: nava.moran{at}huji.ac.il.

In the animal world the regulation of ion channels by phosphoinositides (PIs) has been investigated extensively demonstrating a wide range of channels controlled by phosphatidylinositol (4,5)bisphosphate (PtdInsP2). To understand PI regulation of plant ion channels we examined the in-Planta effect of PtdInsP2 on the K+-efflux channel of tobacco, Nicotiana tabacum Outward-Rectifying K channel (NtORK). We applied patch-clamp in the whole-cell configuration (with fixed "cytosolic" [Ca2+] and pH) to protoplasts isolated from cultured tobacco cells with genetically manipulated plasma-membrane (PM) levels of PtdInsP2 and cellular inositol (1,4,5)trisphosphate: "Low PIs" had depressed levels of these PIs and "High PIs" had elevated levels relative to controls. In all these cells, K channel activity, reflected in the net, steady-state outward K+ currents, IK, was inversely related to the PM PtdInsP2 level. Consistent with this, short-term manipulations decreasing PtdInsP2 levels in the High PIs, such as pretreatment with the phytohormone ABA (25 µM) or neutralizing the bath solution from pH 5.6 to pH 7, increased IK – i.e. NtORK activity. Moreover, increasing PtdInsP2 levels in controls or in ABA-treated High-PIs cells, using the specific PI-PLC inhibitor, U73122 (2.5-4 µM), decreased NtORK activity. In all cases, IK decreases stemmed largely from decreased maximum-attainable NtORK channels conductance and partly from shifted voltage dependence of channel gating to more positive potentials, making it more difficult to activate the channels. These results are consistent with NtORK inhibition by the negatively-charged PtdInsP2 in the internal PM leaflet. Such effects are likely to underlie PI signaling in intact plant cells.






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