Two Different Conductances Contribute to the Anion Currents in Coffea arabica Protoplasts

Two Different Conductances Contribute to the Anion Currents in Coffea arabica Protoplasts The anion conductance of the plasma membrane of Coffea arabica protoplasts was isolated and characterized using the whole-cell patch clamp technique. Voltage pulse protocols revealed two components: a voltage-gated conductance (G s ) and a voltage-independent one (G l ). G s is activated upon depolarization (e-fold activation every +36 mV) with time constants of 1 sec and 5 sec at all potentials. G l and G s also differ by their kinetic and biophysical properties. In bi-ionic conditions the current associated with G s shows strong outward rectification and its permeability sequence is F− > NO3 − > Cl−. In the same conditions the current associated with G l does not rectify and its permeability sequence is F−≫ NO3 −= Cl−. Furthermore, at potentials over +50 mV G s , but not G l , increases with a time constant of several minutes. Finally the gating of G s is affected by stretch of the membrane, which leads to an increased activation and a reduced voltage sensitivity. Anion conductances similar to the ones described here have been found in many plant preparations but G l -type components have been generally interpreted as the background activation of the slow voltage-gated channels (corresponding to G s ). We show that in coffee protoplasts G l and G s are kinetically and biophysically distinct, suggesting that they correspond to two different molecular entities. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of Membrane Biology Springer Journals

Two Different Conductances Contribute to the Anion Currents in Coffea arabica Protoplasts

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Publisher
Springer-Verlag
Copyright
Copyright © 1997 by Springer-Verlag New York Inc.
Subject
Life Sciences; Biochemistry, general; Human Physiology
ISSN
0022-2631
eISSN
1432-1424
D.O.I.
10.1007/s002329900271
Publisher site
See Article on Publisher Site

Abstract

The anion conductance of the plasma membrane of Coffea arabica protoplasts was isolated and characterized using the whole-cell patch clamp technique. Voltage pulse protocols revealed two components: a voltage-gated conductance (G s ) and a voltage-independent one (G l ). G s is activated upon depolarization (e-fold activation every +36 mV) with time constants of 1 sec and 5 sec at all potentials. G l and G s also differ by their kinetic and biophysical properties. In bi-ionic conditions the current associated with G s shows strong outward rectification and its permeability sequence is F− > NO3 − > Cl−. In the same conditions the current associated with G l does not rectify and its permeability sequence is F−≫ NO3 −= Cl−. Furthermore, at potentials over +50 mV G s , but not G l , increases with a time constant of several minutes. Finally the gating of G s is affected by stretch of the membrane, which leads to an increased activation and a reduced voltage sensitivity. Anion conductances similar to the ones described here have been found in many plant preparations but G l -type components have been generally interpreted as the background activation of the slow voltage-gated channels (corresponding to G s ). We show that in coffee protoplasts G l and G s are kinetically and biophysically distinct, suggesting that they correspond to two different molecular entities.

Journal

The Journal of Membrane BiologySpringer Journals

Published: Feb 4, 2014

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