Conduction and blocking properties of a predominantly anion-selective channel from human platelet surface membrane reconstituted into planar phospholipid bilayers

1432-1424

platelet surface membrane ; lipid bilayer ; anion channel ; ion selectivity ; block

Springer Online Journal Archives 1860-2000

Biology

Chemistry and Pharmacology

Summary We have investigated the basic properties of a predominantly anion-selective channel derived from highly purified human platelet surface membrane. Single channels have been reconstituted into planar phospholipid bilayers by fusion of membrane vesicles and recorded under voltage-clamp conditions. The channel is found to have the following properties: (i) Channel activity occurs in bursts of openings separated by long closed periods. (ii) The current-voltage relationship is nonlinear. Channel current is seen to rectify, with less current flowing at positive than at negative voltages. Rectification may be due to asymmetric block by HEPES/Tris buffers. In 450mm KCl, 5mm HEPES/Tris, pH 7.2 the single channel conductance at −40 mV is ∼160 pS and at +40 mV is ∼90 pS. (iii) The conductanceconcentration relationship follows a simple saturation curve. Half maximal conductance is achieved at a concentration of ∼1000mm KCl, and the curve saturates at a conductance of ∼500 pS. (iv) Reversal potentials interpreted in terms of the Goldman-Hodgkin-Katz equation indicate a Cl∶K permeability ratio of 4∶1. (v) The channel accepts all of the halides as well as a number of other anions. The following sequence of relative anion permeabilities (in the presence of K+) is obtained: F−〈acetate−〈gluconate−〈Cl−〈Br−〈I−〈NO 3 − 〈SCN−. (vi) Cations as large as TEA+ are permeant. (vii) Current through the channel is blocked in the presence of DIDS, SITS and ATP, but not by Zn2+.

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