Alzheimer's β-Amyloid, Human Islet Amylin, and Prion Protein Fragment Evoke Intracellular Free Calcium Elevations by a Common Mechanism in a Hypothalamic GnRH Neuronal Cell Line*

A growing number of reports suggest that elevated levels of extracellular Alzheimer's β-amyloid protein alter the homeostasis of free [Ca2+] i in different cell types of the mammalian brain. In line with these results, we have previously shown that AβP[1–40] forms cation-selective channels (Ca2+ included) across artificial planar bilayers formed from acidic phospholipids and across excised membrane patches from immortalized hypothalamic GnRH neurons (GT1-7 cells), suggesting that the nonregulated Ca2+-influx through these spontaneously formed “amyloid channels” may provide a mechanism to explain its toxicity (1). We have now found and report here that the application of AβP[1–40] to GT1-7 neurons consistently elevates [Ca2+] i levels. We also found that human islet amylin and the prion protein fragment (PrP106–126), peptides that acquire β-pleated sheet conformation in water solutions and have been reported to form ion channels across planar bilayer membranes, also increase cytosolic free calcium in GT1-7 neurons. Searching for protective agents, we found that soluble cholesterol, known to decrease the fluidity of the cell membrane, inhibits AβP[1–40]-evoked [Ca2+] i rise. These results suggest that unregulated Ca2+ entry across amyloid channels may be a common mechanism causing cell death, not only in diseases of the third age, including Alzheimer's disease and type 2 diabetes mellitus, but also in prion-induced diseases.