Pardaxin-stimulated calcium uptake in pc12 cells is blocked by cadmium and is not mediated by l-type calcium channels

Pardaxin is an excitatory neurotoxin which triggers neurotransmitter release as a result of voltage-dependent pore formation within the neuronal membrane. We have used several pharmacological manipulations of calcium influx to characterize pardaxin pore activity in PC12 cells in culture. Pardaxin stimulates the uptake of radioactive calcium into PC12 cells in a dose dependent fashion (EDso of 0.4//M). This stimulation is partially inhibited by nifedipine, a blocker of L-type calcium channels. Effective blockade of pardaxin stimulation was produced by the inorganic calcium channel blockers cadmium (ICso of 10//M) and nickel (2 mM). Homologous down regulation of L-calcium channels by the agonist Bay K-8644, inhibited the subsequent stimulation of calcium uptake by this drug, but not by pardaxin. A fluorometric analysis of pardaxin pore formation in unilamellar large liposomes indicates pardaxin pores are blocked by cadmium (10-200//M). These data distinguish between pardaxin pores and L-type calcium channels in PC12 cells. We suggest pardaxin as a pharmacological ionophore tool to modulate neuronal calcium homeostasis and neurotransmitter release.