  Recent molecular dynamics simulations (Herce and Garcia, PNAS, 104: 20805
(2007)) have suggested that the arginine-rich HIV Tat peptides might be able to
translocate by destabilizing and inducing transient pores in phospholipid
bilayers. In this pathway for peptide translocation, arginine residues play a
fundamental role not only in the binding of the peptide to the surface of the
membrane but also in the destabilization and nucleation of transient pores
across the bilayer, despite being charged and highly hydrophilic. Here we
present a molecular dynamics simulation of a peptide composed of nine arginines
(Arg-9) that shows that this peptide follows the same translocation pathway
previously found for the Tat peptide. We test this hypothesis experimentally by
measuring ionic currents across phospholipid bilayers and cell membranes
through the pores induced by Arg-9 peptides. We find that Arg-9 peptides, in
the presence of an electrostatic potential gradient, induce ionic currents
across planar phospholipid bilayers, as well as in cultured osteosarcoma cells
and human smooth muscle cells freshly isolated from the umbilical artery. Our
results suggest that the mechanism of action of Arg-9 peptide involves the
creation of transient pores in lipid bilayers and cell membranes.
