Alzheimer's amyloid-beta peptide inhibits sodium/calcium exchange measured in rat and human brain plasma membrane vesicles.
Na+/Ca2+ exchange activity was measured by monitoring vesicular Ca2+ content after incubation in buffers containing 45Ca2+. When Na+-loaded vesicles were placed into Na+-free buffer, vesicular Ca2+ content increased rapidly and reached a plateau after two to three minutes. Only preaggregated amyloid-beta1-40 (Abeta1-40) and Abeta25-35 reduced vesicular Ca2+ content. Both peptides produced a maximal reduction in Ca2+ content of approximately 50%. The peptides reduced Ca2+ content with similar potency and half maximal effects were seen at less than 10 microM for Abeta25-35. Calcium-loaded vesicles mediate a rapid Ca2+/Ca2+ exchange, which also was inhibited by aggregated Abeta25-35. Aggregated Abeta25-35 did not affect the passive Ca2+ permeability of the vesicles. Aggregated Abeta25-35 reduced Ca2+ content in plasma membrane vesicles isolated from normal and Alzheimer's disease frontal cortex with less potency but the same efficacy as seen in rat brain. Aggregated Abeta25-35 did not produce nonspecific effects on vesicle morphology such as clumping or loss of intact vesicles. When placed in the buffer used to measure Ca2+ content, Congo Red at molar ratios of less than one blocked the inhibitory effect of preaggregated Abeta25-35. When added in equimolar concentrations to freshly dissolved and unaggregated Abeta25-35, Congo Red also was effective at blocking the inhibitory effect on Ca2+ content. In contrast, vitamin E (antioxidant) and N-tert-butyl-alpha-phenylnitrone (spin trapping agent) failed to block the inhibitory action of aggregated Abeta25-35. The exact mechanisms of Abeta-induced neurotoxicity in cell culture has yet to be solved. Accumulation of free radicals play a necessary role, but disruptions of Ca2+ homeostasis are also important. The data presented here are consistent with a proposed mechanism where aggregated Abeta peptides directly interact with hydrophobic surfaces of the exchanger protein and/or lipid bilayer and interfere with plasma membrane Ca2+ transport.
Wu
A
A
Department of Biological Sciences, Ohio University College of Osteopathic Medicine, Athens 45701, U.S.A.
Derrico
C A
CA
Hatem
L
L
Colvin
R A
RA
D000544:Alzheimer Disease / Q000378:metabolism*; D000595:Amino Acid Sequence; D016229:Amyloid beta-Peptides / Q000737:chemistry / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D018699:Coated Vesicles / Q000187:drug effects / Q000378:metabolism*; D003224:Congo Red / Q000494:pharmacology; D005625:Frontal Lobe / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008969:Molecular Sequence Data; D008985:Monensin / Q000494:pharmacology; D010446:Peptide Fragments / Q000737:chemistry / Q000494:pharmacology*; D051381:Rats; D012964:Sodium / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger / Q000378:metabolism*
D016229:Amyloid beta-Peptides; D010446:Peptide Fragments; D019831:Sodium-Calcium Exchanger; C078592:amyloid beta-protein (1-40); C074636:amyloid beta-protein (25-35); D003224:Congo Red; D008985:Monensin; D012964:Sodium; D002118:Calcium