Dissociation between the Joro spider toxin sensitivity of recombinant alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors and their ability to increase intracellular calcium.
We compared the toxin sensitivity, Ca2+ flux response and rectification properties of recombinant alpha-amino-3-hydroxy-5-methyl-4-isoazolepropionic acid (AMPA) receptors obtained by transfecting human embryonic kidney (HEK) 293 cells with different ratios of GluR1 and GluR2 cDNAs (10:1 to 1:10). Simultaneous measurements of kainate-activated Ca2+ fluxes and inward currents, using fura-2 microfluorimetry under voltage clamp conditions, suggested the existence of GluR2 containing channels which are permeable to Ca2+ and insensitive to Joro spider toxin (JSTx). Imaging experiments showed that JSTx inhibition of the Ca2+ response induced by kainate was reduced by increasing the relative amount of GluR2. However, even at GluR1/GluR2(R) ratios of 1:1 and 1:4, cells were still able to flux Ca2+ when stimulated by kainate. GluR2 similarly inhibited the ability of JSTx to reduce kainate-evoked inward currents in whole cell patch-clamp experiments. Variations in the rectification properties of the AMPA currents, induced by changes in the cDNA ratio, were not always correlated with the changes in toxin sensitivity and [Ca2+]i response. Thus, cells with almost linear I-V relationships were partially blocked by JSTx and still Ca2+ permeable. Our results indicate a dissociation between the toxin sensitivity and Ca2+ flux through GluR2 containing AMPA receptors and suggest that receptors with diverse Ca2+ permeabilities are generated by the expression of variable amounts of GluR2.
Meucci
O
O
Department of Pharmacological and Physiological Sciences, The University of Chicago, IL 60637, USA.
Miller
R J
RJ
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D007608:Kainic Acid / Q000494:pharmacology; D009498:Neurotoxins / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D018091:Receptors, AMPA / Q000187:drug effects* / Q000378:metabolism; D011994:Recombinant Proteins; D013111:Spider Venoms / Q000494:pharmacology*
D002118:Calcium; D007608:Kainic Acid; D009498:Neurotoxins; D018091:Receptors, AMPA; D011994:Recombinant Proteins; D013111:Spider Venoms; C044936:JSTX spider toxin; C104722:glutamate receptor ionotropic, AMPA 2