Prion protein fragment 106-126 potentiates catecholamine secretion from PC-12 cells

The toxic actions of scrapie prion protein (PrP(sc)) are poorly understood. We investigated the ability of the toxic PrP(sc) fragment 106-126 to interfere with evoked catecholamine secretion from PC-12 cells. Prion protein fragment 106-126 (PrP106-126) caused a time- and concentration-dependent augmentation of exocytosis due to the emergence of a Ca(2+) influx pathway resistant to Cd(2+) but sensitive to other inorganic cations. In control cells, secretion was dependent on Ca(2+) influx through L- and N-type Ca(2+) channels, but after exposure to PrP106-126, secretion was unaffected by N-type channel blockade. Instead, selective L-type channel blockade was as effective as Cd(2+) in suppressing secretion. Patch-clamp recordings revealed no change in total Ca(2+) current density in PrP106-126-treated cells or in the contribution to total current of L-type channels, but a small Cd(2+)-resistant current was found only in PrP106-126-treated cells. Thus PrP106-126 augments secretion by inducing a Cd(2+)-resistant Ca(2+) influx pathway and alters coupling of native Ca(2+) channels to exocytosis. These effects are likely contributory factors in the toxic cellular actions of PrP(sc).