Effect of hypoxia on nuclear high affinity Ca2+ ‐ATPase activity and nuclear Ca2+ ‐influx in the cerebral cortex of newborn piglets (888.2)

Abstract

Nuclear calcium signals control a number of critical nuclear functions including regulation of transcription factors, cell cycle regulation, gene transcription and DNA replication. Previous studies have shown that during hypoxia, there is increase in intracellular Ca2+‐and in nuclear high affinity Ca2+‐ATPase activity in the cerebral cortex of newborn piglets.We test the hypothesis that hypoxia results in increased activity of high affinity Ca2+‐ATPase and increased concentration of Ca2+‐influx in cortical neuronal nuclei of newborn piglets, and this hypoxia‐induced increase is Src kinase mediated.Piglets were divided into normoxic (Nx, n=4), hypoxic (Hx, n=4), and hypoxic pretreated with Src kinase inhibitor (Hx+Srci, n=4). Hypoxia was induced by decreasing FiO2 to 0.07 for 1 hr. Src kinase inhibitor (PP2, 1.0 mg/kg i.v.) was administered 30 min prior to hypoxia. Hypoxia was documented by levels of ATP and phosphocreatine (PCr). Nuclear 45Ca2+ concentration and activity of high affinity Ca2+‐ATPase was determined at 37°C for 30 min.Nuclear 45Ca2+ ‐influx (pmoles/mg protein) was 3.95±0.57 in Nx , 13.36±1.56 in Hx (p<0.05) and 9.61±2.76 in the Hx+Srci group. Ca2+‐ATPase activity increased following hypoxia: from 244.66±73.55 nmol Pi/mg protein/h in the normoxic group to 426.33±94.99 nmol Pi/mg protein/h in the hypoxic group (p<0.05 vs. normoxic group). In the Hx+Srci group, the high affinity Ca2+‐ATPase activity increased to 354.25±62.88 nmol Pi/mg protein/h (p<0.05 vs. hypoxic group). The data show that administration of PP2, a selective inhibitor of Src kinase, prevents the hypoxia‐induced increase in nuclear 45Ca2+ ‐influx concentration and Ca2+‐ATPase activity.We conclude that the hypoxia‐induced increase in nuclear membrane high affinity Ca2+‐ATPase activity is Src kinase‐mediated activation of the high affinity Ca2+‐ATPase, a mechanism of ATP‐dependent Ca2+uptake may lead to increase in intranuclear Ca2+during hypoxia.Grant Funding Source: NIH HD200337