The Effects of Salts and Sugars on the Plasma Membrane Permeabilizing Activity of Polycationic Peptides Derived from Protoxins

Abstract

Polycationic peptides with high activity in mitochondria permeabilization were derived from natural protoxins. Their capacity to permeabilize the plasma membrane was studied using red blood cells incubated in isotonic media with different salts (LiCl, NaCl, KCl, choline chloride) and/or sugars (mannitol, sucrose, raffinose). The addition of valinomycin induced high membrane potential (negative inside) and caused cell shrinkage with the rate that seemed to be mainly restricted by the plasma membrane permeability to anions (in isotonic salt and/or sugar media with 0.1 mM KCl, but not in KCl medium). Under these conditions, permeabilizing activity of the peptides was significantly higher in choline chloride and low ionic strength sugar media. Before swelling, fast shrinkage of the cells was caused by some relatively short peptides at concentrations of 0.25-2.0 μM in NaCl/sugar (1:1 osmotic contribution) or choline chloride media. The first derivative of the shrinkage traces coincided with the first derivative of the membrane potential drop. The rate of cell swelling decreased with an increase in the molecule size of sugar or polyethylene glycol. The initial phase of cell shrinkage was also observed in the absence of valinomycin, but at significantly higher peptide concentrations. We suggest that the cell shrinkage induced by polycationic peptides is due to anion selectivity of the peptide pores at the initial step of their formation. The obtained data contribute to a better understanding of the mechanism of biomembrane permeabilization by anticancer and antimicrobial polycationic peptides. (Colciencias grant #111840820380 and the National University of Colombia grant #20101007930).