Interaction of extracellular potassium and cesium with the kinetics of inward rectifying K+ channels in the plasma membrane of mesophyll protoplasts of Avena sativa
1996
Kourie, J.I. (Yale Univ., Connecticut (USA))
Using the patch-clamp technique the kinetics of whole-cell and single channel inwardly rectifying K+ currents were measured in enzymatically-isolated protoplasts from Avena sativa mesophyll leaf cells. the hyperpolarization-activated whole-cell current had an initial K+ component (Iki) and a time-dependent K+ component which reaches steady state (Ikss) within 500 ms. After an initial delay, the activation of Ikss and the deactivation of the tail K+ current (Ikt) followed an exponential time course. The time-constants of activation (tau-a), at 10 mM and 50 mM [K+]o, and of deactivation (tau-d) could be described by exponential and sigmoidal dependence on membrane voltage (Vm), respectively. The relative number of the activated K+ channel population increased sigmoidally as a function of hyperpolarized Vm. On the other hand, the relative number of the deactivated K+ channel population decreased exponentially as a function of hyperpolarized Vm. The kinetics of the inward rectifying K+ current were dependent on Vm but not on extracellular K+ concentration, [K+]o
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