Effect of nitric oxide synthase inhibition on high affinity Ca2+-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-L-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 Rye 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. Tn the nitrated group the enzyme activity increased to 554+/-59 nmol Pi/mg protein/h (P<0.05). Thus peroxynitrire-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. (C) 2000 Elsevier Science B.V. All rights reserved.