beta-Amyloid[1-40]-induced early hyperpolarization in M26-1F cells, an immortalized rat striatal cell line

The short-term (20-minute) action of beta[1-40]-amyloid on the resting transmembrane potential was investigated by means of flow-cytofluorimetric studies in M26-1F cells, an immortalized rat striatal cell line, using the potential-sensitive fluorescent probe bis-oxonol. The distribution of the individual cell-associated probe fluorescence was found to be shifted to lower levels in cells treated with beta-amyloid[1-40] for 20 minutes as compared with that of their untreated counterparts. A change in the same direction was caused by valinomycin, a hyperpolarizing ionophore, whereas gramicidin, a depolarizing ionophore, induced a shift to higher fluorescence intensities. These findings, together with the reported behaviour of this particular fluorescent probe at different transmembrane potential levels, indicate that beta-amyloid[1-40] is capable of inducing early hyperpolarization in M26-1F cells. This is one of the earliest cell physiological effect of beta-amyloid peptides that has been reported so far. Moreover, our findings indicate an ionophore-like action of amyloid peptides.