Evaluation of β-amyloid peptide 25-35 on calcium homeostasis in cultured rat dorsal root ganglion neurons

Accumulation of beta-amyloid (Abeta) protein in brain is an important characteristic for the etiology of Alzheimer's disease. Of all the possible processes generating the neurotoxic effects by Abeta, disruption of intracellular Ca2+ homeostasis is the primary event. In this process, various intracellular Ca2+ regulatory mechanisms are reported to be involved. Using patch-clamp techniques, both low and high voltage activated Ca2+ channel currents were recorded in the cultured dorsal root ganglion (DRG) neurons. Application of Abeta protein fragment, Abeta(25-35) (2 muM), for 30 s increased the amplitude in both currents. The Abeta-triggered facilitation effect of Ca2+ channel was found in all the depolarized potentials tested, as shown in the current-voltage relationship. Furthermore, after applying single cell Ca2+ microfluorometric method, it was found that Abeta(25-35) alone Could trigger elevations of intracellular Ca2+ concentration ([Ca2+](i)) level in 90% of the cells tested. The elevation diminished completely by cumulatively adding CdCl2, NiCl2, thapsigargin (TG), FCCP and ZN(2+) in the normal bath solution. Combining pharmacological approaches, we found that voltage-dependent Ca2+ channels, Ca2+ stores and a putative Zn2+-sensitive extracellular Ca2+ entry, respectively, makes 61.0, 25.1, and 13.9% contribution to the [Ca2+](i) increase caused by Abeta. When tested in a Ca2+-free buffer, mitochondria was found to contribute 41.3% of Abeta produced [Ca2+](i) elevation and the remaining 58.7% was attributed to endoplasmic reticulum (ER) release. (C) 2002 Elsevier Science B.V. All rights reserved.