, Volume 159, Issue 1, pp 83-94
Date: 04 Feb 2014

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

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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.

Received: 25 November 1996/Revised: 9 April 1997