A major prion protein (PrP) mutant that forms amyloid fibrils in the diseased brain of patients with Gerstmann-Sträussler-Scheinker syndrome (GSS) is a fragment of 7 kDa spanning from residues 81-82 to 144-153 of PrP. Analysis of ionic membrane currents, recorded with a lipid bilayer technique, revealed that the wild-type fragment PrP(82-146) WT and the partially scrambled PrP(82-146) (127-146) SC are capable of forming heterogeneous ion channels that are similar to those channels formed with PrP(106-126). In contrast, PrP(82-146) peptides in which the region from residue 106 to 126 had been scrambled (SC) showed a reduction in interaction with lipid membranes and did not form channels. The PrP(82-146) WT- and PrP(82-146) (127-146) SC-formed cation channels with fast kinetics are Cu2+ sensitive and rifampicin (RIF) insensitive, whereas the time-dependent inactivating channels formed by these same peptides are both Cu2+ and RIF insensitive. The presence of RIF in the solution before the addition of PrP(82-146) WT or PrP(82-146) (127-146) SC affected their incorporation into the lipid bilayers. PrP(82-146) WT and PrP(82-146) (127-146) SC fast cation channels formed in the presence of RIF appeared in an electrically semisilent state or an inactivated state. Increasing [Cd2+]cis enhanced the incorporation of PrP(82-146) WT and PrP(82-146) (127-146) SC channels formed in the presence of RIF. We conclude that the major PrP mutant fragment in the diseased brain of GSS patients is prone to form channels in neuronal membranes, causing their dysfunction. We propose that Cd2+ may accentuate the neurotoxicity of this channel-forming PrP fragment by enhancing its incorporation into the membrane.