Increased intraneuronal resting [Ca²⁺] in adult Alzheimer’s disease mice

Neurodegeneration in Alzheimer's disease (AD) has been linked to intracellular accumulation of misfolded proteins and dysregulation of intracellular Ca2+. In the current work, we determined the contribution of specific Ca2+ pathways to an alteration in Ca2+ homeostasis in primary cortical neurons from an adult triple transgenic (3xTg-AD) mouse model of AD that exhibits intraneuronal accumulation of beta-amyloid proteins. Resting free Ca2+ concentration ([Ca2+](i)), as measured with Ca2+-selective microelectrodes, was greatly elevated in neurons from 3xTg-AD and APP(SWE) mouse strains when compared with their respective non-transgenic neurons, while there was no alteration in the resting membrane potential. In the absence of the extracellular Ca2+, the [Ca2+](i) returned to near normal levels in 3xTg-AD neurons, demonstrating that extracellular Ca2+contributed to elevated [Ca2+](i). Application of nifedipine, or a non-L-type channel blocker, SKF-96365, partially reduced [Ca2+](i). Blocking the ryanodine receptors, with ryanodine or FLA-365 had no effect, suggesting that these channels do not contribute to the elevated [Ca2+](i). Conversely, inhibition of inositol trisphosphate receptors with xestospongin C produced a partial reduction in [Ca2+](i). These results demonstrate that an elevation in resting [Ca2+](i), contributed by aberrant Ca2+entry and release pathways, should be considered a major component of the abnormal Ca2+ homeostasis associated with AD.