Sodium Fluxes through Nonselective Cation Channels in the Plasma Membrane of Protoplasts from Arabidopsis Roots

• Published in: Plant physiology (Bethesda) Vol. 128; no. 2; pp. 379 - 387
• Main Authors: Vadim Demidchik, Tester, Mark
• Format: Journal Article
• Language: English
• Published: Rockville, MD American Society of Plant Biologists 01.02.2002; American Society of Plant Physiologists
• Subjects: Arabidopsis - cytology; Arabidopsis - metabolism; Biological and medical sciences; Biological Transport, Active - drug effects; Calcium Channel Blockers - pharmacology; Cations; Cations - metabolism; Cations - pharmacology; Cell Membrane Permeability - drug effects; Cell membranes; Cell physiology; Cesium - metabolism; Cesium - pharmacology; Corn; Electric potential; Environmental Stress and Adaptation; Fundamental and applied biological sciences. Psychology; Guard cells; Ion channels; Ion Channels - metabolism; Ion Transport - physiology; Lithium - metabolism; Lithium - pharmacology; Membrane Potentials - drug effects; Patch-Clamp Techniques; Plant cells; Plant physiology and development; Plant roots; Plant Roots - cytology; Plant Roots - metabolism; Plants; Plasma membrane and permeation; Potassium - metabolism; Potassium - pharmacology; Potassium Chloride - pharmacology; Protoplasts; Protoplasts - drug effects; Protoplasts - physiology; Quaternary Ammonium Compounds - metabolism; Quaternary Ammonium Compounds - pharmacology; Rubidium - metabolism; Rubidium - pharmacology; Rye; Sodium - metabolism; Tetraethylammonium Compounds - pharmacology; Calcium; Cell permeability; Root; Ionic channel; Biological activity; Arabidopsis thaliana; Regulation(control); Ionic selectivity; Sodium; Cruciferae; Dicotyledones; Protoplast; Angiospermae; Plasma membrane; Cations; Spermatophyta; Ionic conductance; Experimental plant
• DOI: 10.1104/pp.010524
• ISSN: 0032-0889

The aim of the present work was to characterize Na+ currents through nonselective cation channels (NSCCs) in protoplasts derived from root cells of Arabidopsis. The procedure of the protoplast isolation was modified to increase the stability of Arabidopsis root protoplasts in low external Ca2+ by digesting tissue in elevated Ca2+. Experiments in whole-cell and outside-out modes were carried out. We found that Na+ currents in Arabidopsis root protoplasts were mediated by cation channels that were insensitive to externally applied $\text{tetraethylammonium}^{+}$ and verapamil, had no time-dependent activation (permanently opened or completely activated within 1-2 ms), were voltage independent, and were weakly selective for monovalent cations. The selectivity sequence was as follows: K+ (1.49) > NH4 + (1.24) > Rb+ (1.15) ≈ Cs+ (1.10) ≈ Na+ (1.00) > Li+ (0.73) > $\text{tetraethylammonium}^{+}$ (0.47). Arabidopsis root NSCCs were blocked by H+ (pK ≈ 6.0), Ca2+ (K1/2 ≈ 0.1 mM), Ba2+, Zn2+, La3+, Gd3+, quinine, and the His modifier diethylpyrocarbonate. They were insensitive to most organic blockers (nifedipine, verapamil, flufenamate, and amiloride) and to the SH-group modifier p-chloromercuriphenyl sulfonic acid. Voltage-insensitive, Ca2+-sensitive single channels were also resolved. Properties of Arabidopsis root NSCCs are discussed and compared with characteristics of similar conductances studied previously in plants and animals. It is suggested that NSCCs present a distinct group of plant ion channels, mediating toxic Na+ influx to the cell and probably having other important roles in physiological processes of plants.