Naspm (1-Naphthyl acetyl spermine), a synthetic analogue of Joro spider toxin, is a calcium permeable AMPA (CP-AMPA) receptors antagonist. In Vitro: NASPM selectively suppresses the inwardly rectifying and Ca²⁺-permeable AMPA receptors expressed in type II neurons. It has no effect on AMPA receptors in type I neurons. At -60 mV, NASPM suppresses AMPA receptors in type II neurons with an IC₅₀ value of 0.33 µM. The blocking effect of NASPM on the Ca²⁺-permeable AMPA receptors is use and voltage-dependent^[1].