MEMBRANE-PROTEIN ALTERATIONS IN RODENT ERYTHROCYTES AND SYNAPTOSOMES DUE TO AGING AND HYPEROXIA

We have applied the technique of electron paramagnetic resonance (EPR) protein-specific spin labeling to the study of membrane protein alter ations occurring during age and exposure to isobaric hyperoxia. Cortic al synaptosomes and erythrocyte membranes (ghosts) were isolated from young rodents (Fisher 344 rats or mongolian gerbils, 3-4 months of age ) and aged rodents (age 22-27 months for rats, greater than 15 months for gerbils). Membrane proteins were spin labeled with the thiol-speci fic spin label MAL-6 (2,2,6,6,-tetramethyl-4-maleimido-piperdin- 1-oxy l). The relevant EPR spectral parameter of MAL-6 labeled membranes, th e W/S ratio, decreased significantly with age of animal in both synapt osomes and ghosts (P < 0.001). As a paradigm for accelerated oxidative stress, young and aged gerbils were exposed to an atmosphere of 90-10 0% O-2 for 0-48 h. In both young and aged gerbils, the W/S ratio decre ased significantly with hyperoxic stress (P < 0.003). The W/S ratio of synaptosomes isolated from aged gerbils decreased continually from 0- 48 h hyperoxia, whereas the W/S ratio of synaptosomes from young anima ls demonstrated a pronounced rebound effect from 24-48 h. The results are discussed with reference to membrane protein oxidation in aging.