Optical control of calcium‐permeable AMPA receptors by azobenzene–spermines

Background and Purpose Photo‐switchable compounds acting on ion channels are valuable tools for neuroscience. Specific ligands have been developed for many channels, but selective compounds providing effective optical control for calcium‐permeable α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA) receptors are still lacking. Because the difference between calcium‐permeable and impermeable receptors is localised in the channel selectivity filter, the only feasible approach to discriminate between them is to design photo‐switchable pore blockers. We have, here, synthesised azobenzene derivatives of spermine and investigated their actions. Experimental Approach The biological activity of azobenzene–spermines was studied in electrophysiological experiments using isolated rat brain neurons, synaptic transmission in slices, fly larvae neuromuscular junction and recombinant AMPA receptors expressed in CHO cells. The experimental results were rationalised using computer modelling. Key Results The most active compound, azobenzene–spermine‐6 (ABSP‐6), selectively blocked calcium‐permeable AMPA receptors in low nanomolar concentrations under ambient light, with an IC 50 under illumination, three orders of magnitude higher. Using rat brain slices, ABSP‐6 provided optical control of excitatory postsynaptic current (EPSC) mediated by AMPA receptors in giant interneurons of striatum, while EPSCs in cortical pyramidal neurons were unaffected. Computer modelling suggests that in the light‐induced cis configuration, formation of an intramolecular H bond reduces the effective length of polyamine chain, resulting in marked loss of activity. Conclusions and Implications Our work provides the first effective optical control of calcium‐permeable AMPA receptors, suited to neurophysiological studies. It will be crucial in elucidating the localisation of glutamate receptor subtypes and clarifying their role in various processes.