Redox-dependent modulation of the carrot SV channel by cytosolic pH.
Currents mediated by a slow vacuolar (SV) channel were recorded and characterized in vacuoles from cultured carrot cells. The carrot channel shows the typical functional characteristics reported for channels of the SV category previously identified in other plants, i.e., slow voltage-dependent activation kinetics, current activation favoured by cytosolic calcium and permeability to different monovalent cations. The carrot channel is strongly activated by cytosolic reducing agents (such as dithiothreitol, DTT, and glutathione, GSH) and has a peculiar dependence on cytosolic pH, which, in turn, is affected by the concentration of cytosolic reducing agents. Specifically, in 1 mM DTT or GSH the channel displayed a maximum conductance at neutral pH. The normalized conductance did not depend significantly on DTT concentration at acidic pH, while at alkaline pH the attenuation of the normalized conductance declines with increasing DTT concentration. Our results suggest two pH-titratable groups within the carrot SV channel, one of these depending on cysteine residues exposed to the cytosolic side of the vacuole.
Scholz-Starke
Joachim
J
Istituto di Biofisica, Consiglio Nazionale delle Ricerche, Via De Marini 6, 16149 Genova, Italy. scholz@ge.ibf.cnr.it
De Angeli
Alexis
A
Ferraretto
Cristiana
C
Paluzzi
Silvio
S
Gambale
Franco
F
Carpaneto
Armando
A
D015220:Calcium Channels / Q000502:physiology*; D002478:Cells, Cultured; D003600:Cytosol / Q000502:physiology; D018552:Daucus carota / Q000502:physiology*; D004229:Dithiothreitol / Q000494:pharmacology; D005978:Glutathione / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007473:Ion Channels / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D010084:Oxidation-Reduction; D010940:Plant Proteins / Q000502:physiology
D015220:Calcium Channels; D007473:Ion Channels; D010940:Plant Proteins; D005978:Glutathione; D004229:Dithiothreitol