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 (Gs) and a voltage-independent one (Gl). Gs is activated upon depolarization (e-fold activation every +36 mV) with time constants of 1 sec and 5 sec at all potentials. Gl and Gs also differ by their kinetic and biophysical properties. In bi-ionic conditions the current associated with Gs shows strong outward rectification and its permeability sequence is F- > NO3- > Cl-. In the same conditions the current associated with Gl does not rectify and its permeability sequence is F- > > NO3- = Cl-. Furthermore, at potentials over +50 mV Gs, but not Gl, increases with a time constant of several minutes. Finally the gating of Gs 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 Gl-type components have been generally interpreted as the background activation of the slow voltage-gated channels (corresponding to Gs). We show that in coffee protoplasts Gl and Gs are kinetically and biophysically distinct, suggesting that they correspond to two different molecular entities.
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Laboratorio de Biofísica, Centro Internacional de Física, Ciudad Universitaria, Bogotá, Colombia.
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D000838:Anions / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D003069:Coffee / Q000502:physiology*; D004553:Electric Conductivity; D015640:Ion Channel Gating; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D008536:Meglumine / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D008962:Models, Theoretical; D018408:Patch-Clamp Techniques; D011523:Protoplasts / Q000502:physiology; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D000838:Anions; D003069:Coffee; D007473:Ion Channels; D013757:Tetraethylammonium Compounds; D019789:Tetraethylammonium; D008536:Meglumine