In a similar manner, experiments using neurons cultured from transgenic AD mice have reported that intraneuronal Ab increases the vulnerability of neurons to stressful cellular environments such as excitotoxicity and oxidative stress. In some cases, the intraneuronal expression of Ab itself can trigger apoptotis of neurons via a p53-dependent mechanism. It is worth noting that one simplistic manner in which exogenous Ab may induce neurodegenerative changes in Tg2576 neurons is due to uptake of Ab via LRP1, which increases intracellular Ab levels above a threshold level leading to decreased viability and alterations in tau distribution and phosphorylation. However, two pieces of evidence argue against this possibility. Firstly, the distribution of endogenous Ab and internalised Ab in Tg2576 is quite different, suggesting that these two pools of Ab are not able to act in the same manner. And secondly, our MIFE studies demonstrate rapid and direct changes in ionic homeostasis of Tg2576 neurons triggered by application of exogenous Ab, indicating that exogenously applied Ab is probably acting in a different manner to intracellular endogenous Ab. While the studies discussed above have provided important information PSB 0739 regarding the effect of extracellular and intracellular Ab upon cultured neurons, it is important to consider that AD is a progressive condition, in which neurons are likely to be continuously exposed to sublethal concentrations of both intracellular and extracellular Ab. To more accurately model this situation, Tg2576 neurons were cultured in the presence of extracellular Ab. This RG 102240 combination of intra- and extracellular Ab induced caspase-3 dependent apoptosis of Tg2576 but not wildtype neurons. To elucidate the mechanisms underlying this, we used a non-invasive MIFE approach to observe changes in net ion flux of K + and H + ions in response to Ab. Using this approach, we were able to continuously observe net ion flux of K + and H + for more than 2 hours. We found that Ab treatment of wildtype neurons caused an immediate efflux of K +, which gradually returned to homeostasis within 10 minutes. However, we found that Abtreated Tg2576 neurons were unable to maintain K + homeostasis, leading to prolonged leakage of K + out of neurons. K + efflux from cells is a key early initiator of apoptosis, as a low potassium intracellular microenvironment assists apoptosome formation and the activation of caspases and endonucleases.