Abstract
1. The effect of synthetic joro spider toxin (JSTX-3) on alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor channels in cultured rat hippocampal neurones was investigated using the whole-cell patch-clamp technique. 2. A population of cultured neurones had AMPA receptors with strong inward rectification and substantial Ca2+ permeability (type II neurones), whereas most neurones (type I neurones) had slight outward rectification and little Ca2+ permeability. JSTX-3 selectively suppressed the inwardly rectifying and Ca(2+)-permeable AMPA receptors expressed in type II neurones without affecting AMPA receptors in type I neurones. 3. The effect of JSTX-3 on the Ca(2+)-permeable AMPA receptors was use and voltage dependent. In the steady state, current responses induced by ionophoretic applications of kainate (a non-desensitizing agonist of AMPA receptors) were suppressed by the toxin in a dose-dependent manner at negative potentials (IC50 = 56 nM at -60 mV). 4. At the standard membrane potential (-60 mV), recovery from the blockage by JSTX-3 was very slow. Even after washout for more than 7 min, the recovery was only partial. However, the blockage was completely removed immediately after application of a +60 mV voltage pulse for 5 s in conjunction with a single ionophoretic application of kainate.