Calcium stores in cultured fibroblasts and their changes with Alzheimer's disease

The experiments in this paper identify multiple calcium compartments in cultured human fibroblasts and reveal abnormalities in one of these pools in cells from Alzheimer patients. In the presence of external calcium, bradykinin (BK) increased cytosolic free calcium ([Ca2+](i)) about 3-fold and then [Ca2+](i) rapidly declined. Omission of calcium from the media did not affect the BK-induced peak, which indicates that the peak reflects internal stores. Other compounds that also released calcium from internal stores included A23187 (a calcium ionophore), thapsigargin (Tg; an inhibitor of endoplasmic reticulum ATPase), and FCCP (an uncoupler of oxidative phosphorylation). The [Ca2+](i) response to sequential addition of compounds in calcium-free media identified discrete internal calcium stores. BK depleted internal calcium pools such that subsequent stimulation with BK, FCCP or bombesin did not increase [Ca2+](i). However, A23187 or thapsigargin still elicited responses. A23187 depleted essentially all internal calcium pools. Either Tg or FCCP reduced the calcium stores that could be released by BK or A23187. Thus, cellular calcium compartments that respond to BK and A23187 partially overlap. The common pool includes Tg- and FCCP-sensitive compartments. Calcium stores were examined in cells from Alzheimer disease patients, because previous studies suggest that their calcium homeostasis is altered. A23187 addition to BK-treated cells produced a 95% greater response in cell Lines from Alzheimer patients (n = 7) than in those from controls (n = 5). Thus, various calcium stores can be pharmacologically distinguished in fibroblasts and at least one of these compartments is abnormal in Alzheimer's disease.