Preferential inhibition by a novel Na+/Ca2+ channel blocker NS-7 of severeto mild hypoxic injury in rat cerebrocortical slices: A possible involvement of a highly voltage-dependent blockade of Ca2+ channel

The hypoxic injury was induced in rat cerebrocortical slices by the exposur e to hypoxia for 45 min in the absence or presence of 3 mM glucose, followe d by reoxygenation for 5 h. The injury was more pronounced in the absence o f glucose (severe hypoxic injury) than in the presence of glucose (mild hyp oxic injury). A novel Na+/Ca2+ channel blocker, NS-7 [4-(4-fluorophenyl)-2- methyl-6-(5-piperidinopentyloxy) pyrimidine hydrochloride], at 3 to 30 mu M inhibited preferentially the severe hypoxic injury, whereas MK-801, omega- conotoxin GVIA (omega-CTX), and N-G-nitro-L-arginine methylester suppressed preferentially the mild hypoxic injury. The extracellular cyclic GMP forma tion, a marker of nitric oxide synthesis, was enhanced during hypoxia, alth ough the extent was greater in the absence of glucose. As observed in the h ypoxic injury, NS-7 preferentially inhibited the cyclic GMP formation induc ed by severe hypoxic insults, whereas MK-801 or omega-CTX reduced it under mild hypoxic condition. When 30 to 50 mM KCl was applied to normoxic slices , a concentration-dependent increase in the extracellular cyclic GMP format ion was observed. NS-7 blocked the cyclic GMP formation induced by 50 mM KC l but not by 30 to 40 mM KCl, whereas omega-CTX suppressed only the 30 mM K Cl-evoked response. In primary neuronal culture, NS-7 reversed KCl-induced increase in intracellular Ca2+ in which the inhibition was marked when the KCl concentration was increased. These findings suggest that NS-7, unlike o ther neuroprotective compounds used in this study, is more effective in sev ere hypoxic injury. The highly voltage-dependent Ca2+ channel blockade may contribute to the mode of neuroprotective action of NS-7.