Pharmacological profile and anti-ischemic properties of the Ca(2+)-channel blocker NS-638

Included in the sequence of events leading to neuronal death in ischemic tissue following stroke is an excessive and toxic rise in the intracellular CA(2+)-concentration, predominantly due to an influx of Ca2+ through nonselective cation-channels as well as CA(2+)-channels. In the present study we have characterized the pharmacological profile and anti-ischemic effects of 2-amino-1-(4-chlorobenzyl)-5-trifluoromethylbenzimidazole (NS-638), a small nonpeptide molecule with CA(2+)-channel blocking properties. NS-638 dose dependently inhibited K(+)-stimulated [45Ca2+]-uptake in chick cortical synaptosomes and 2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA)-stimulated [3H]GABA-release from cultured cortical neurons with IC50 values of 2.3 and 4.3 microM, respectively. K(+)-stimulated intracellular CA(2+)-elevation in cultured cerebellar granule cells was equipotently blocked with an IC50 value of 3.4 microM. At this concentration no effect on CA(2+)-induced contractions in K(+)-depolarized guinea pig taenia coli was observed. The effect of NS-638 on neuronal CA(2+)-channels was evaluated using whole cell patch clamp techniques. The compound reversibly blocked N- and L-type CA(2+)-channels in cultured chick dorsal root ganglion cells in the concentration range of 1-30 microM. In the mouse middle cerebral artery occlusion (MCAO) model, NS-638 administered i.p. (50 mg kg-1) at 1 h and 6 h post-ischemia, and once a day for the next two days, resulted in a 48% reduction in total infarct volume. The compound did not show protection against ischemic neuronal damage in the gerbil model of bilateral carotid artery occlusion (BCAO). This data suggests, that neuronal CA(2+)-channel blockers may have potential in ameliorating the pathological damage after focal ischemia.