Rapid solution application methods

A conserved structural mechanism of NMDA receptor inhibition: A comparison of ifenprodil and zinc

Zinc and ifenprodil induce similar conformational changes in the NMDA receptor, suggesting a conserved mechanism of inhibition independent of receptor subtype and the site at which the inhibitor binds.

N-methyl-d-aspartate (NMDA) receptors, one of the three main types of ionotropic glutamate receptors (iGluRs), are involved in excitatory synaptic transmission, and their dysfunction is implicated in various neurological disorders. NMDA receptors, heterotetramers typically composed of GluN1 and GluN2 subunits, are the only members of the iGluR family that bind allosteric modulators at their amino-terminal domains (ATDs). We used luminescence resonance energy transfer to characterize the conformational changes the receptor undergoes upon binding ifenprodil, a synthetic compound that specifically inhibits activation of NMDA receptors containing GluN2B. We found that ifenprodil induced an overall closure of the GluN2B ATD without affecting conformation of the GluN1 ATD or the upper lobes of the ATDs, the same mechanism whereby zinc inhibits GluN2A. These data demonstrate that the conformational changes induced by zinc and ifenprodil represent a conserved mechanism of NMDA receptor inhibition. Additionally, we compared the structural mechanism of zinc inhibition of GluN1–GluN2A receptors to that of ifenprodil inhibition of GluN1–GluN2B. The similarities in the conformational changes induced by inhibitor binding suggest a conserved structural mechanism of inhibition independent of the binding site of the modulator.

Achieving synaptically relevant pulses of neurotransmitter using PDMS microfluidics

Fast synaptic transmission is mediated by post-synaptic ligand-gated ion channels (LGICs) transiently activated by neurotransmitter released from pre-synaptic vesicles. Although disruption of synaptic transmission has been implicated in numerous neurological and psychiatric disorders, effective and practical methods for studying LGICs in vitro under synaptically relevant conditions are unavailable. Here, we describe a novel microfluidic approach to solution switching that allows for precise temporal control over the neurotransmitter transient while substantially increasing experimental throughput, flexibility, reproducibility, and cost-effectiveness. When this system was used to apply ultra-brief ( approximately 400micros) GABA pulses to recombinant GABA(A) receptors, members of the cys-loop family of LGICs, the resulting currents resembled hippocampal inhibitory post-synaptic currents (IPSCs) and differed from currents evoked by longer, conventional pulses, illustrating the importance of evaluating LGICs on a synaptic timescale. This methodology should therefore allow the effects of disease-causing mutations and allosteric modulators to be evaluated in vitro under physiologically relevant conditions.