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Titolo:
MULTIPLE INWARD CHANNELS PROVIDE FLEXIBILITY IN NA+ K+ DISCRIMINATIONAT THE PLASMA-MEMBRANE OF BARLEY SUSPENSION-CULTURE CELLS/
Autore:
AMTMANN A; LAURIE S; LEIGH R; SANDERS D;
Indirizzi:
UNIV YORK,DEPT BIOL,POB 373 YORK YO1 5YW N YORKSHIRE ENGLAND ROTHAMSTED EXPT STN,DEPT BIOCHEM & PHYSIOL HARPENDEN AL5 2JQ HERTS ENGLAND
Titolo Testata:
Journal of Experimental Botany
, volume: 48, anno: 1997,
pagine: 481 - 497
SICI:
0022-0957(1997)48:<481:MICPFI>2.0.ZU;2-2
Fonte:
ISI
Lingua:
ENG
Soggetto:
RECTIFYING K+ CHANNELS; PLANAR LIPID BILAYERS; SALT TOLERANCE; RYE ROOTS; PATCH-CLAMP; GUARD-CELLS; ARABIDOPSIS-THALIANA; XYLEM PARENCHYMA; CATION CHANNEL; ION CHANNELS;
Keywords:
ANION CHANNEL; K+-INWARD RECTIFIER; NONSELECTIVE CATION CHANNEL; PATCH CLAMP; SALT-TOLERANCE;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
49
Recensione:
Indirizzi per estratti:
Citazione:
A. Amtmann et al., "MULTIPLE INWARD CHANNELS PROVIDE FLEXIBILITY IN NA+ K+ DISCRIMINATIONAT THE PLASMA-MEMBRANE OF BARLEY SUSPENSION-CULTURE CELLS/", Journal of Experimental Botany, 48, 1997, pp. 481-497

Abstract

Ion transport across the plasma membrane of suspension-culture cells derived from immature barley embryos has been studied in low (15 mM KCl) and high (additional 150 mM NaCl) salt conditions to understand howplants discriminate between K+ and Na+ during ion uptake. In both media about 50% of the cells exhibited resting potentials more negative than any of the passive diffusion potentials. In whole-cell patch clampexperiments membrane hyperpolarization activated large inward currents. Whilst the instantaneous current components did not discriminate between K+ and Na+, the time-dependent current, I-in, was selective for K+ over Na+. Further analysis of I-in revealed the following properties: double exponential current activation (time-constants 0.03 s and 0.3 s, half activation potential similar to 171 mV); no inactivation; complete block by Ba2+ (30 mM in 100 mM KCl) and part block by TEA(+) (maximum 50% with 20 mM); dependence on millimolar concentrations of cytoplasmic ATP; no block by external or cytoplasmic Na+. The selectivitysequences K+ >> Rb+ > NH4+ > Na+ >> Cl- and K+ >> NH4+ > Na+ > Rb+ were determined from measurements of reversal potentials and relative steady-state currents respectively. P-NA:P-K was 0.07+/-0.02 (from reversal potentials) and I-Na:I-K was 0.17+/-0.05 (from relative currents). A high variance among the observed permeability ratios suggested thatseveral channels with different ion-selectivities contributed to the time-dependent whole-cell currents. In single channel experiments, several inward channels with distinct properties were found. The major channels were voltage-gated, K+-selective channel (12 pS), (ii) an ATP-activated non-selective cation channel (7 pS) and (iii) an inward-rectifying anion-channel (150 pS, all unitary conductances given for 100 mMKCl). No significant differences were found in whole-cell currents orsingle-channel characteristics between cells that had been adapted toa high-salt growth-medium (150 mM NaCl) and non-adapted cells. The idea that differential regulation of plasma membrane ion channels gives rise to a physiological flexibility, allowing the cells to control Nauptake under varying external conditions, is discussed.

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Documento generato il 28/11/20 alle ore 18:44:10