Blocking effect of 1-naphthyl acetyl spermine on Ca 2+-permeable AMPA receptors in cultured rat hippocampal neurons

Abstract

Effects of 1-naphthyl acetyl spermine (NASPM), a synthetic analogue of Joro spider toxin (JSTX), on α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors were studied in cultured rat hippocampal neurons using the whole-cell patch clamp technique. A population of cultured neurons had AMPA receptors with a strong inward rectification and a high permeability to Ca 2+ (type II neurons), whereas most neurons (type I neurons) had AMPA receptors with a slight outward rectification and little Ca 2+ permeability. NASPM selectively suppressed the inwardly rectifying and Ca 2+-permeable AMPA receptors expressed in type II neurons. It had no effect on AMPA receptors in type I neurons. The blocking effect of NASPM on the Ca 2+-permeable AMPA receptors was use and voltage-dependent. When the effect of NASPM reached a steady state, current responses induced by ionophoretic applications of kainate, a non-desensitizing agonist of AMPA receptors, in type II neurons were suppressed by NASPM in a dose-dependent manner at −60 mV (IC 50 0.33 μM, and Hill coefficient 0.94). The response to kainate recovered partially after washing out NASPM. NASPM did not affect the Ca 2+-permeable AMPA receptors when the neuronal membrane was held at potentials more positive than +40 mV. Furthermore, the blockade by NASPM which was attained at negative potentials was transiently removed by shifting membrane potential to +60 mV for 5 s together with a single ionophoretic application of kainate. NASPM would be useful as a pharmacological tool for elucidating both physiological and pathological significances of Ca 2+-permeable AMPA receptors in the CNS.