Precise spatiotemporal control of voltage-gated sodium channels by photocaged saxitoxin

Here we report the pharmacologic blockade of voltage-gated sodium ion channels (NaV) by a synthetic saxitoxin derivative affixed to a photocleavable protecting group. We demonstrate that a functionalized saxitoxin (STX-eac) enables exquisite spatiotemporal control of NaV blockade to interrupt action potentials (APs) in dissociated neurons and nerve fiber bundles. The photo-uncaged inhibitor (STX-ea) is a nanomolar potent, reversible binder of NaVs. We use STX-eac to reveal differential susceptibility of myelinated and unmyelinated axons in the corpus callosum to NaV-dependent alterations in AP propagation, with unmyelinated axons preferentially showing reduced AP fidelity under conditions of partial NaV blockade. These results validate STX-eac as a high precision tool for robust photocontrol of neuronal excitability and AP generation.