Differential modulation of alpha 3 beta 2 and alpha 3 beta 4 neuronal nicotinic receptors expressed in Xenopus oocytes by flufenamic acid and niflumic acid.
Effects of flufenamic acid (FFA) and niflumic acid (NFA), which are often used to block Ca(2+)-activated Cl- current, have been investigated in voltage-clamped Xenopus oocytes expressing alpha 3 beta 2 and alpha 3 beta 4 nicotinic ACh receptors (nAChRs). NFA and FFA inhibit alpha 3 beta 2 nAChR-mediated inward currents and potentiate alpha 3 beta 4 nAChR-mediated inward currents in normal, Cl(-)-free and Ca(2+)-free solutions to a similar extent. The concentration-dependence of the inhibition of alpha 3 beta 2 nAChR-mediated ion current yields IC50 values of 90 microM for FFA and of 260 microM for NFA. The potentiation of alpha 3 beta 4 nAChR-mediated ion current by NFA yields an EC50 value of 30 microM, whereas the effect of FFA does not saturate for concentrations of up to 1 mM. At 100 microM, FFA reduces the maximum of the concentration-effect curve of ACh for alpha 3 beta 2 nAChRs, but leaves the EC50 of ACh unaffected. The same concentration of FFA potentiates alpha 3 beta 4 nAChR-mediated ion currents for all ACh concentrations and causes a small shift of the concentration-effect curve of ACh to lower agonist concentrations. The potentiation, like the inhibition, is most likely due to a noncompetitive effect of FFA. Increasing ACh-induced inward current either by raising the agonist concentration from 10 microM to 200 microM or by coapplication of 10 microM ACh and 200 microM FFA causes a similar enhancement of block of the alpha 3 beta 4 nAChR-mediated ion current by Mg2+. This suggests that the effects of FFA and of an increased agonist concentration result in a similar functional modification of the alpha 3 beta 4 nAChR-operated ion channel. It is concluded that alpha 3 beta 4 and alpha 3 beta 2 nAChRs are oppositely modulated by FFA and NFA through a direct beta-subunit-dependent effect.
Zwart
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R
Research Institute of Toxicology, Utrecht University, The Netherlands.
Oortgiesen
M
M
Vijverberg
H P
HP
D000818:Animals; D018118:Chloride Channels / Q000187:drug effects* / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D005260:Female; D005439:Flufenamic Acid / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects*; D009474:Neurons / Q000737:chemistry; D009544:Niflumic Acid / Q000494:pharmacology*; D009865:Oocytes; D018408:Patch-Clamp Techniques; D011978:Receptors, Nicotinic / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis* / Q000235:genetics; D014982:Xenopus laevis
D018118:Chloride Channels; D011978:Receptors, Nicotinic; D011993:Recombinant Fusion Proteins; D009544:Niflumic Acid; D005439:Flufenamic Acid