Inhibition of glutamate uptake by a polypeptide toxin (phoneutriatoxin 3-4) from the spider Phoneutria nigriventer

Glutamate concentration increases significantly in the extracellular compar tment during brain ischaemia and anoxia. This increase has an important Ca2 +-independent component, which is due in part to the reversal of glutamate transporters of the plasma membrane of neurons and glia. The toxin phoneutr iatoxin 3-4 (Trx3-4) from the spider Phoneutria nigriventer has been report ed to decrease the evoked glutamate release from synaptosomes by inhibiting Ca2+ entry via voltage-dependent Ca2+ channels. However, we report here th at Tx3-4 is also able to inhibit the uptake of glutamate by synaptosomes in a time-dependent manner and that this inhibition in turn leads to a decrea se in the Ca2+-independent release of glutamate. No other polypeptide toxin so far described has this effect. Our results suggest that Tx3-4 can be a valuable tool in the investigation of function and dysfunction of glutamate rgic neurotransmission in diseases such as ischaemia.