Blockade of voltage-sensitive sodium channels by NS-7, a novel neuroprotective compound, in the rat brain

The effects of 4-(4-fluorophenyl)-2-methyl-6-(5-piperidinopentyloxy) pyrimidine hydrochloride (NS-7), a novel neuroprotective compound, on the voltage-sensitive sodium channels (VSSC) were examined in the rat brain and cardiac myocytes. NS-7 inhibited [H-3]batrachotoxinin A 20 alpha-benzoate (BTX) binding (neurotoxin receptor site 2) in brain membranes with a Ki value of 1 mu M, while the compound was less effective in the cardiac myocytes (Ki = 13 mu M). Aconitine, on the other hand, inhibited [H-3]BTX binding to brain membranes and cardiac myocytes with the same potency. In contrast, NS-7 had no affinity for [H-3]saxitoxin binding in brain (neurotoxin receptor site 1). In superfused slices of the rat cerebral cortex, NS-7 inhibited the veratridine (5 mu M)-evoked glutamate release in a concentration-dependent manner, the IC50 value of which was 7.7 mu M, whereas the compound showed a weak and not significant suppression of KCl-evoked glutamate release. The tissue concentrations of NS-7 in the rat cerebral cortex and heart were 89 and 28 nmole/g tissue, respectively, 5 min after its intravenous injection (8 mg/kg). Furthermore, in the cerebral cortex, NS-7 distributed preferentially to the membrane-enriched synaptosomal fraction. Since neurotoxin receptor site 2 is located in the transmembrane region of the VSSC moiety, the channel function may be substantially inhibited by a peripheral administration of NS-7. These results suggest that the blockade of neurotoxin receptor site 2 of VSSC in the brain contributes to the neuroprotective action of NS-7.