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Keywords:

  • Pardaxin;
  • Bilayer;
  • Phospholipid;
  • Membrane;
  • Anion;
  • Cation;
  • Selectivity;
  • Single channel;
  • Current;
  • Voltage

Abstract

Using the method of bilayer membranes at the tip of a patch pipette, the properties of the ionic channels produced by the ionophore toxin pardaxin were investigated. At low toxin concentrations, voltage-dependent, single-channel events were measured. The current-voltage curves were non-linear when determined in Tris-CI solution, but were linear in K+-HEPES solution. Using asymmetric ion solutions, the ionic selectivity of pardaxin channels was estimated from the reversal potentials obtained. The sequence of the relative permeabilities for monovalent cations was Tl+ > Rb+ > Cs+ > K+,NH4+ > methylamine+ > Li+ > dimethylamine+ > Na+. Except for Li+, the selectivity sequence fitted the cations relative hydrated size. For bivalent ions the permeability of Ba2+, Sr2+, and Mn2+ relative to Mg2+ changed according to the relative hydrated size. For anions the selectivity sequence was I > NO3 > Br > CI > CIO4 > SCN > BF > HCOO > F > CH3COO. The selectivity sequence for the small anions (I, NO3, Br, CI) was different from their hydrated size. Pardaxin channel showed a modest ion selectivity between small anions and cations (PK:PCI:PNa = 1.28:1.00:0.56). Pardaxin is proposed as a biophysical model to study ionic channel selectivity. © 1995 Wiley-Liss, Inc.