Calcium oscillations in type-1 astrocytes, the effect of a presenilin 1 (PS1) mutation

Stimulation of type-1 astrocytes, by a number of agonists, has been shown to increase cytosolic Ca2+ concentrations in an oscillatory manner. However, it is unknown how these are driven or altered by aging, injury or disease. Therefore, we characterized the signaling properties of rat type-1 astrocytes in monolayer cultures. Ca2+ responses were recorded in astrocytes stimulated with ATP or glutamate. Oscillations were evident in cultures at 3 days in vitro (DIV 3) with a peak percentage (26%) of cells responding by DIV 7. The presence or absence of serum in the culture medium did not influence this percentage. Likewise, long-term culture (DIV 30+) did not increase the oscillating cell numbers. ATP was found to have a more potent effective dose (50 μM) than glutamate (10 mM). Membrane potential was recorded with fluorescent voltage-sensitive dye (membrane potential dye for FLIPR™) and was similar regardless of the culture age and intracellular Ca2+ response. This suggests that mechanisms associated with the intracellular release of Ca2+ from endogenous Ca2+ stores, rather than ion fluxes across the plasma membrane, may contribute to the oscillations in the astrocytes. In order to identify a possible pathological significance of this response, we transfected astrocytes with wild-type presenilin (PS1) as well as PS1 harboring a mutation linked to familial Alzheimer's disease (FAD). PS mutation expressing astrocytes oscillated at lower ATP and glutamate concentrations when compared to wild-type PS1 expressing astrocytes. This indicates that PS1 mutation may introduce aberrations in the intracellular Ca2+ mobilization in astrocytes contributing to the accelerated pathogenesis in FAD.