The Ca2+ influx induced by beta-amyloid peptide 25-35 in cultured hippocampal neurons results from network excitation.
Although a neurotoxic role has been postulated for the beta-amyloid protein (beta AP), which accumulates in brain tissues in Alzheimer's disease, a precise mechanism underlying this toxicity has not been identified. The peptide fragment consisting of amino acid residues 25 through 35 (beta AP25-35), in particular, has been reported to be toxic in cultured neurons. We report that beta AP25-35, applied to rat hippocampal neurons in culture, caused reversible and repeatable increases in the intracellular Ca2+ concentration ([Ca2+]i), as measured by fura 2 fluorimetry. Furthermore, beta AP25-35 induced bursts of excitatory potentials and action potential firing in individual neurons studied with whole cell current clamp recordings. The beta AP25-35-induced [Ca2+]i elevations and electrical activity were enhanced by removal of extracellular Mg2+, and they could be blocked by tetrodotoxin, by non-N-methyl-D-aspartate (NMDA) and NMDA glutamate receptor antagonists, and by the L-type Ca2+ channel antagonist nimodipine. Similar responses of bursts of action potentials and [Ca2+]i increases were evoked by beta AP1-40. Responses to beta AP25-35 were not prevented by pretreatment with pertussis toxin. Excitatory responses and [Ca2+]i elevations were not observed in cerebellar neuron cultures in which inhibitory synapses predominate. Although the effects of beta AP25-35 depended on the activation of glutamatergic synapses, there was no enhancement of kainate- or NMDA-induced currents by beta AP25-35 in voltage-clamp studies. We conclude that beta AP25-35 enhances excitatory activity in glutamatergic synaptic networks, causing excitatory potentials and Ca2+ influx. This property may explain the toxicity of beta AP25-35.
Brorson
J R
JR
Department of Neurology, University of Chicago, Illinois 60637, USA.
Bindokas
V P
VP
Iwama
T
T
Marcuccilli
C J
CJ
Chisholm
J C
JC
Miller
R J
RJ
D016229:Amyloid beta-Peptides / Q000633:toxicity*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D018698:Glutamic Acid / Q000502:physiology; D009415:Nerve Net / Q000502:physiology*; D010446:Peptide Fragments / Q000633:toxicity*; D017966:Pyramidal Cells / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D009435:Synaptic Transmission / Q000187:drug effects
D016229:Amyloid beta-Peptides; D010446:Peptide Fragments; C078592:amyloid beta-protein (1-40); C074636:amyloid beta-protein (25-35); D018698:Glutamic Acid; D002118:Calcium