Inwardly rectifying whole cell potassium current in human blood eosinophils

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Abstract
1 Membrane currents were studied in single human blood eosinophils using the whole cell voltage clamp technique. The whole cell current‐voltage relationship exhibited rectification about the membrane potential which followed the potassium equilibrium potential when [K+]o was raised. Elevation of [K+]o considerably potentiated inward current amplitude, and in some cells channel activity was discernible in the whole cell membrane current recordings. The single channel conductance was 24 ± 1 pS ([K+]o, 100 mM; [K+]i, 140 mM), and eosinophils were found to have as few as three, and on average twenty, inward rectifier channels each. 2 The inward current was inhibited in a voltage‐dependent manner by extracellular cations in order of potency Ba2+ > Cs+ > Na+. Intracellular acidification inhibited while alkalization augmented the inward current. Mg2+ contributed to rectification as dialysis with nominally Mg2+‐free pipette solution was associated with an increase in the outward current during membrane polarization. 3 By reverse transcription‐polymerase chain reaction (RT‐PCR) using suitable primers on human eosinophil mRNA, an inward rectifier channel, Kir2.1, was identified, which is known from expression studies to have very similar properties to those found in this study. 4 Superoxide anion production or its stimulation by phorbol 12‐myristate 13‐acetate (PMA) was not significantly affected by depolarization with 140 mM [K+]o, or by 1 mM BaCl2. 5 It is concluded that the single channel currents and the whole cell current rectification observed in human blood eosinophils resulted from the presence of an inwardly rectifying potassium channel, probably Kir2.1.