Modulation of Ca2+ channel currents in primary cultures of rat cortical neurones by amyloid beta protein (1-40) is dependent on solubility status

Abstract

The Alzheimer's disease peptide amyloid beta protein (Abeta) can exist in soluble and fibrillar, aggregated forms. Abeta in the aggregated form is thought to be pro-apoptotic, causing cell death when applied to cultured neurones by disrupting Ca(2+) homeostasis. This process may involve changes in Ca(2+) influx across the plasma membrane. The aim of this study was to quantify this effect by applying both the aggregated and unaggregated forms of Abeta to cultured rat cortical neurones. Unaggregated Abeta(1-40) (24-h pretreatment, 1 microM) stimulated an increase in voltage-dependent Ca(2+) channel current activity, which was found to comprise of N- and P-type current. In the aggregated form, Abeta(1-40) pre-treatment reduced Ca(2+) channel current density in cortical neurones via an action on N-type Ca(2+) current. This failure of aggregated Abeta(1-40) to increase the Ca(2+) channel current was confirmed on cerebellar granule neurone Ca(2+) currents which normally undergo an increase in activity following soluble Abeta application. Using the MTT and TUNEL assays, aggregated Abeta(1-40) was found to promote apoptotic cell death in cortical neurones confirming that Abeta exhibited the expected biological activity. Unaggregated Abeta had no neurotoxic effect. These data indicate that the unaggregated, non-pathological form of Abeta(1-40), and not the aggregated form, cause changes in neuronal Ca(2+) channel activity. This may reflect a normal functional role for amyloid peptides in the central nervous system.