TIME-COURSE OF PROTEIN-CHANGES FOLLOWING IN-VITRO ISCHEMIA IN THE RATHIPPOCAMPAL SLICE

Following 5 min in vitro ischemia, total protein synthesis is dramatic ally and persistently inhibited in neurons in the rat hippocampal slic e. This model system was used to explore the responses of individual p roteins to this irreversible insult. In vitro ischemia inhibited new p rotein synthesis of most proteins analyzed; however, the synthesis of a 68/70 kDa protein was substantially stimulated for the first hour af ter ischemia. By 3 h postischemia, its synthesis rates were depressed to 60% of control rates. Although the total amounts of most proteins w ere not significantly depleted for the first few hours after an ischem ic episode, there were several notable exceptions. The levels of HSC73 , a constitutively expressed member of the 70 kDa stress protein famil y, were reduced after in vitro ischemia. In addition, MAP-2 (microtubu le-associated protein-2) and alpha-tubulin were depleted in the early hours after the insult, with MAP-2 exhibiting a detectable depletion e arlier than tubulin. In contrast, the levels and distribution of a 68 kDa neurofilament protein localized to CA3 pyramidal neurons in the sl ice, apparently distinct from the band whose new synthesis was stimula ted, were not affected by the 5 min in vitro ischemia insult. Thus, th e responses of individual proteins to ischemia varied considerably. Th ese individual responses could play an important role in the damage me chanism that is initiated in response to in vitro ischemia.