Effects of N-(2-propylpentanoyl) urea on nmda receptor subtype NR1A/NR2B Expressed in xenopus laevis oocytes

Abstract

The main goal of this study was to gain insight into the mechanisms underlying the anticonvulsant activity of N-(2-Propylpentanoyl)Urea (VPU), a new synthetic valproate derivative, on NR1AINR2B NMDA receptors subtype using the two-electrode voltage-clamp technique in Xenopus laevis oocytes injected with cRNAs. Application of VPU (1-300 ) µM) produced no changes on the membrane conductance of Xenopus oocytes . However, coapplication of glutamate (0.01 - 300 µM) and 1OµM glycine induced inward currents with a dose-response curve giving the EC50 of glutamate at 2.26±0.31 µM. Whereas 1 mM of VPA produced very marginal effect, VPU (100- 300 µM) exerted a reversible and competitive inhibition of glutamate response on NR1AINR2B NMDA receptor characterized by shifting the glutamate concentration curve to the right with no alteration of maximal response. Similar response was elicited by AP5, a selective, competitive NMDA binding site antagonist at the concentration of 10 µM. Thus the inhibitory of VPU seems to be comparatively weaker than AP5. Furthermore, based on the results that the inhibitory effects of 100 µM VPU on inward currents induced by 3 µM glutamate did not alter either when the holding potential was stepwise increased from -150 to + 50mV or when different concentration of glycine, a co-agonist of glutamate , was co-applied , it is apparent that antagonistic effect of VPU on glutamate-induced inward current was neither voltage nor glycine dependent. In addition, it was found that VPU (100-300 µM) significantly decrease stimulatory effect of spermine on glutamate response. Taken into consideration that polyamines has been reported to be increased on the face of seizure or ischemia, it is suggestive that inhibitory effect of VPU on NR1AINR2B NMDA receptors , though rather weak , may, in concert with its effect on GABAA receptor and perhaps with some other mechanism that remain to be identified , contribute to its anticonvulsant effect in vivo.