Selective sensitivity of synaptosomal membrane function to cerebral cortical hypoxia in newborn piglets

The effect of hypoxia on the structure and function of the synaptosomal membranes and myelin fraction (glial cells, neuronal cells bodies and axonal membranes) was investigated by measuring Na+,K(+)-ATPase activity and levels of lipid peroxidation products in cerebral cortical synaptosomal membranes and myelin fractions obtained from newborn piglets. Hypoxic hypoxia was induced and cerebral hypoxia was documented as a decrease in the ratio of phosphocreatine to inorganic phosphate (PCr/Pi) using 31P-NMR spectroscopy. PCr/Pi decreased from baseline of 2.93 +/- 0.76 to 0.61 +/- 0.36 during hypoxia. The synaptosomal membrane Na+,K(+)-ATPase activity decreased from a control value of 56.6 +/- 3.7 to 40.4 +/- 6.0 mumol Pi/mg protein/h during hypoxia. The level of conjugated dienes increased from zero (reference value) to 4.5 +/- 2.7 nmol/mg lipid and the level of fluorescent compounds increased from 23.5 +/- 2.2 to 92.6 +/- 46.4 ng quinine sulfate/mg lipid in the synaptosomal membranes during hypoxia. No change in myelin fraction Na+,K(+)-ATPase activity or levels of lipid peroxidation products were noted. These data indicate that synaptosomal membranes, rich in polyunsaturated fatty acids, are more susceptible to oxygen free radical mediated lipid peroxidative damage during hypoxia.