Summary
The apical membrane of epithelial cells from the A6 cell line grown on impermeable substrata was studied using the patch-clamp technique. We defined the apical membrane as that membrane in contact with the growth medium. In about 50% of the patches, channels with single-unit conductances of 360±45 pS in symmetrical 105mm NaCl solutions, and characteristic voltage-dependent inactivation were observed. Using excised membrane patches and varying the ionic composition of the bathing medium, we determined that the channels were anion selective, with a permeability ratio for Cl− over Na+ of about 9∶1, calculated from the reversal potential using the constantfield equation. The channel was most active at membrane potentials between ±20 mV and inactivated, usually within a few seconds, at higher potentials of either polarity. Reactivation from this inactivation was slow, sometimes requiring minutes. In addition to its fully open state, the channel could also enter a flickering state, which appeared to involve rapid transitions to one or more submaximal conductance levels. The channel was inhibited by the disulfonic stilbene SITS in a manner characteristic of reversible open-channel blockers.
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Nelson, D.J., Tang, J.M. & Palmer, L.G. Single-channel recordings of apical membrane chloride conductance in A6 epithelial cells. J. Membrain Biol. 80, 81–89 (1984). https://doi.org/10.1007/BF01868692
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DOI: https://doi.org/10.1007/BF01868692