Voltage-dependent blockage of Ca(2+)-permeable AMPA receptors by joro spider toxin in cultured rat hippocampal neurones.
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.
Department of Physiology, School of Medicine, Gunma University, Japan.
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Iino
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Koike
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Isa
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Ozawa
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D004594:Electrophysiology; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D006624:Hippocampus / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D015640:Ion Channel Gating / Q000187:drug effects; D007478:Iontophoresis; D007608:Kainic Acid / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009498:Neurotoxins / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D051381:Rats; D018091:Receptors, AMPA / Q000819:agonists / Q000037:antagonists & inhibitors* / Q000378:metabolism; D013111:Spider Venoms / Q000494:pharmacology*
D018690:Excitatory Amino Acid Agonists; C044936:JSTX spider toxin; D009498:Neurotoxins; D018091:Receptors, AMPA; D013111:Spider Venoms; D007608:Kainic Acid; D002118:Calcium