Effect of nitric oxide synthase inhibition on high affinity Ca-ATPase during hypoxia in cerebral cortical neuronal nuclei of newborn piglets

Previous studies have shown that during hypoxia, neuronal nuclear high affinity Ca²⁺-ATPase activity is increased in the cerebral cortex of newborn piglets. The present study tests the hypothesis that pretreatment with N-nitro- -arginine (NNLA) will prevent the hypoxia-induced increase in high affinity Ca²⁺-ATPase activity in cortical neuronal nuclear membrane of newborn piglets. We also tested the hypothesis that nitration is a mechanism of elevation of the high affinity Ca²⁺-ATPase activity during hypoxia. Studies were performed in five normoxic, five hypoxic, and six NNLA-pretreated (40 mg/kg) hypoxic newborn piglets. Cerebral cortical neuronal nuclei were isolated and the high affinity Ca²⁺-ATPase activity was determined. Further, normoxic samples were aliquoted into two sub-groups for in vitro nitration with 0.5 mM peroxynitrite and subsequent determination of the high affinity Ca²⁺-ATPase activity. The activity increased from 309±40 nmol Pi/mg protein/h in the normoxic group to 520±108 nmol Pi/mg protein/h in the hypoxic group (P<0.05). In the NNLA-pretreated group, the activity was 442±53 nmol Pi/mg protein/h (P<0.05), which is 25% lower than in the hypoxic group. In the nitrated group the enzyme activity increased to 554±59 nmol Pi/mg protein/h (P<0.05). Thus peroxynitrite-induced nitration in vitro increased the high affinity Ca²⁺-ATPase activity and NNLA administration in vivo partially prevented the hypoxia-induced increase in neuronal nuclear high affinity Ca²⁺-ATPase activity. We conclude that the hypoxia-induced increase in nuclear membrane high affinity Ca²⁺-ATPase activity is NO-mediated and that nitration of the enzyme is a mechanism of its modification.