Search

Matrix Metalloproteinase 9 (MMP-9) has been demonstrated to play a crucial role in maintenance of NMDA receptor-dependent LTP and in lateral mobility of these receptors. However, the effect of MMP-9 on NMDA receptor (NMDAR) functional properties is unknown. For this purpose we have investigated the impact of recombinant MMP-9 on the whole-cell NMDAR-mediated current responses in cultured hippocampal neurons. Treatment with MMP-9 induced a reversible acceleration of desensitization and deactivation kinetics but had no effect on current amplitude. Interestingly, phorbol ester, a PKC activator known to enhance NMDAR lateral mobility, induced kinetic changes of currents similar to those produced by MMP-9. In conclusion, our results show that MMP-9 reversibly modulates the NMDAR kinetics and raise a possibility that this modulation could be related to the lateral mobility of these receptors., (© 2009 Wiley-Liss, Inc.)

Background and Purpose: Oenanthotoxin (OETX), a polyacetylenic alcohol from plants of the genus Oenanthe, has recently been identified as potent inhibitor of GABA-evoked currents. However, the effects of OETX on the inhibitory postsynaptic currents (IPSCs), as well as the pharmacological mechanism(s) underlying its effects on GABA(A) receptors, remain unknown. The purpose of this study was to elucidate the mechanism underlying the inhibition of GABAergic currents by OETX., Experimental Approach: Effects of OETX on GABAergic currents were studied using the patch clamp technique on rat cultured hippocampal neurons. Miniature IPSCs (mIPSCs) were recorded in the whole-cell configuration, while the current responses were elicited by ultrafast GABA applications onto the excised patches., Key Results: OETX potently inhibited both mIPSCs and current responses, but its effect was much stronger on synaptic currents. Analysis of the effects of OETX on mIPSCs and evoked currents disclosed a complex mechanism: allosteric modulation of both GABA(A) receptor binding and gating properties and a non-competitive, probably open channel block mechanism. In particular, OETX reduced the binding rate and nearly abolished receptor desensitization. A combination of rapid clearance of synaptic GABA and OETX-induced slowing of binding kinetics is proposed to underlie the potent action of OETX on mIPSCs., Conclusions and Implications: OETX shows a complex blocking mechanism of GABA(A) receptors, and the impact of this toxin is more potent on mIPSCs than on currents evoked by exogenous GABA. Such effects on GABAergic currents are compatible with the convulsions and epileptic-like activity reported for OETX.