Alzheimer's disease amyloid beta-protein forms Zn(2+)-sensitive, cation-selective channels across excised membrane patches from hypothalamic neurons.

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We have previously shown that the 40-residue peptide termed amyloid beta-protein (A beta P[1-40]) in solution forms cation-selective channels across artificial phospholipid bilayer membranes. To determine whether A beta P[1-40] also forms channels across natural membranes, we used electrically silent excised membrane patches from a cell line derived from hypothalamic gonadotrophin-releasing hormone GnRH neurons. We found that exposing either the internal or the external side of excised membrane patches to A beta P[1-40] leads to the spontaneous formation of cation-selective channels. With Cs+ as the main cation in both the external as well as the internal saline, the amplitude of the A beta P[1-40] channel currents was found to follow the Cs+ gradient and to exhibit spontaneous conductance changes over a wide range (50-500 pS). We also found that free zinc (Zn2+), reported to bind to amyloid beta-protein in solution, can block the flow of Cs+ through the A beta P[1-40] channel. Because the Zn2+ chelator o-phenanthroline can reverse this blockade, we conclude that the underlying mechanism involves a direct interaction between the transition element Zn2+ and sites in the A beta P[1-40] channel pore. These properties of the A beta P[1-40] channel are rather similar to those observed in the artificial bilayer system. We also show here, by immunocytochemical confocal microscopy, that amyloid beta-protein molecules form deposits closely associated with the plasma membrane of a substantial fraction of the GnRH neurons. Taken together, these results suggest that the interactions between amyloid beta-protein and neuronal membranes also occur in vivo, lending further support to the idea that A beta P[1-40] channel formation might be a mechanism of amyloid beta-protein neurotoxicity.

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