Evaluation of beta-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 Ca(2+) homeostasis is the primary event. In this process, various intracellular Ca(2+) regulatory mechanisms are reported to be involved. Using patch-clamp techniques, both low and high voltage activated Ca(2+) channel currents were recorded in the cultured dorsal root ganglion (DRG) neurons. Application of Abeta protein fragment, Abeta(25-35) (2 microM), for 30 s increased the amplitude in both currents. The Abeta-triggered facilitation effect of Ca(2+) channel was found in all the depolarized potentials tested, as shown in the current-voltage relationship. Furthermore, after applying single cell Ca(2+) microfluorometric method, it was found that Abeta(25-35) alone could trigger elevations of intracellular Ca(2+) concentration ([Ca(2+)](i)) level in 90% of the cells tested. The elevation diminished completely by cumulatively adding CdCl(2), NiCl(2), thapsigargin (TG), FCCP and Zn(2+) in the normal bath solution. Combining pharmacological approaches, we found that voltage-dependent Ca(2+) channels, Ca(2+) stores and a putative Zn(2+)-sensitive extracellular Ca(2+) entry, respectively, makes 61.0, 25.1, and 13.9% contribution to the [Ca(2+)](i) increase caused by Abeta. When tested in a Ca(2+)-free buffer, mitochondria was found to contribute 41.3% of Abeta produced [Ca(2+)](i) elevation and the remaining 58.7% was attributed to endoplasmic reticulum (ER) release.