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 Ca ²⁺ homeostasis in primary cortical neurons from an adult triple transgenic (3xTg-AD) mouse model of AD that exhibits intraneuronal accumulation of β-amyloid proteins. Resting free Ca²⁺ concentration ([Ca ²⁺]_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.