Simulated ischemia in live cerebral slices is mimicked by opening the Na ⁺ /K ⁺ pump: clues to the generation of spreading depolarization

The gray matter of the higher brain undergoes spreading depolarization (SD) in response to the increased metabolic demand of ischemia, promoting acute neuronal injury and death following stroke, traumatic brain injury, or sudden cardiac arrest. The mechanism linking ischemic failure of the Na⁺/K⁺ ATPase (NKA) pump to the immediate onset of a large inward current driving SD has remained a mystery because blockade of conventional ion channels does not prevent SD nor ischemic neuron death. The marine poison palytoxin (PLTX) specifically binds the NKA at picomolar concentrations, converting this transporter to an open cationic channel, causing sudden neuronal Na⁺ influx and K⁺ efflux. This pump failure, together with induction of a strong inward current, should evoke SD-like activity in gray matter. Indeed, 1-10 nM PLTX applied to live coronal brain slices of rodents induces a propagating depolarization remarkably like SD induced by oxygen/glucose deprivation (OGD). This PLTX depolarization (PD) mimicked other effects of OGD. In the neocortex, as an elevated light transmittance (LT) front passed by an extracellular pipette, a distinct negative DC shift indicated mass cell depolarization, whether induced by bath OGD or PLTX. Either treatment induced strong SD-like responses in the same higher or lower brain regions. Furthermore, we imaged identical real-time OGD-SD or PD effects upon live pyramidal neurons using 2-photon microscopy. Taken together, these findings support our proposal that an endogenous PLTX-like molecule may open the NKA to conduct Na⁺ influx/K⁺ efflux, thereby driving SD and, in its wake, ensuing neuronal damage.<b>NEW & NOTEWORTHY</b> With stroke, traumatic brain injury, or sudden cardiac arrest, there is no therapeutic drug to aid brain recovery. Within 2 min of severe ischemia, a wave of spreading depolarization (SD) propagates through affected gray matter. More SDs arise over hours, expanding the injury. This period represents a therapeutic window to inhibit recurring SD and reduce neuronal damage, but we do not understand the underlying molecular sequence. Here, we argue for a novel molecule to target.