Amyloid ß peptide (25-35) in picomolar concentrations modulates the function of glycine receptors in rat hippocampal pyramidal neurons through interaction with extracellular site(s).

ß-Amyloid peptide (Aß) plays a central role in the pathogenesis of Alzheimer׳s disease, but in lower amounts it is found in normal brains where it participates in physiological processes and probably regulates synaptic plasticity. This study investigated the effects of physiologically relevant concentrations of Aß (1 pM-100 nM), fragment 25-35, on glycine-mediated membrane current in acutely isolated rat hippocampal pyramidal neurons using whole-cell patch-clamp technique. We have found that short (600 ms) co-application of glycine with Aß caused reversible dose-dependent and voltage-independent acceleration of desensitization of glycine current. The peak amplitude of the current remained unchanged. The effect of picomolar Aß concentrations persisted in the presence of 1 µM Aß in the pipette solution, implying that Aß bounds to extracellular site(s). Concentration-dependence curve was N-shaped with maximums at 100 pM and 100 nM, suggesting the existence of two binding sites, which may interact with each other. Glycine current resistant to 100 µM picrotoxin, was insensitive to Aß, which suggests that Aß affected mainly homomeric glycine receptors. When Aß was added to bath solution, besides acceleration of desensitization, it caused reversible dose-dependent reduction of glycine current peak amplitude. These results demonstrate that physiological (picomolar) concentrations of Aß reversibly augment the desensitization of glycine current, probably by binding to external sites on homomeric glycine receptors. Furthermore, Aß can suppress the peak amplitude of glycine current, but this effect develops slowly and may be mediated through some intracellular machinery.