Altered Na+-channel function as an in vitro model of the ischemic penumbra: Action of lubeluzole and other neuroprotective drugs

Veratridine blocks Na+-channel inactivation and causes a persistant Na+-influx. Exposure of hippocampal slices to 10 mu M veratridine led to a failure of synaptic transmission, repetitive spreading depression (SD)-like depolarizations of increasing duration, loss of Ca+-homeostasis, a large reduction of membrane potential, spongious edema and metabolic failure. Normalization of the amplitude of the negative DC shift evoked by high K+ ACSF 80 min after veratridine exposure was taken as the primary endpoint for neuroprotection. Compounds whose mechanism of action includes Na+-channel modulation were neuroprotective (IC50-values in mu M): tetrodotoxin 0.017, verapamil 1.18, riluzole 1.95, lamotrigine greater than or equal to 10, and diphenylhydantoin 16.1. Both NMDA (MK-801 and APH) and non-NMDA (NBQX) excitatory amino acid antagonists were inactive, as were NOS-synthesis inhibitors (nitro-L-arginine and L-NAME), Ca2+-channel blockers (cadmium, nimodipine), and a K+-channel blocker (TEA). Lubeluzole significantly delayed the time before the slices became epileptic, postponed the first SD-like depolarization, allowed the slices to better recover their membrane potential after a larger number of SD-like DC depolarizations, preserved Ca2+ and energy homeostasis, and prevented the neurotoxic effects of veratridine (IC50-value 0.54 mu M). A concentration of lubeluzole, which was 40 X higher than its IC50-value for neuroprotection against veratridine, had no effect on repetitive Na+-dependent action potentials induced by depolarizing current in normal ACSF. The ability of lubeluzole to prevent the pathological consequences of excessive Na+-influx, without altering normal Na+-channel function may be of benefit in stroke.