Rabbits were subjected to
hypoxia (5% O2) for up to 90 min and allowed to recover for a maximum of 4 days. Hippocampus homogenate was assayed for
fodrin breakdown product (BDP). After separation into a nuclear and mitochondrial fraction (NMF), a membrane and microsomal fraction (MMF), and a cytosolic fraction (CF), samples were assayed for
mu-calpain,
m-calpain, and
calpastatin immunoreactivity.
Calpain and
calpastatin immunoreactivity decreased in the NMF and CF but increased in the MMF during
hypoxia and short-term recovery. This translocation occurred in parallel with the increase in
fodrin BDP. Because the increase in the MMF was not large enough to explain the decrease in the other two fractions, it was assumed that the translocation and activation was accompanied by a reduction in the total amounts of calpains and
calpastatin.
Glucocorticoid pretreatment (beta-methasone, 0.4 mg x kg-1 x day-1) for 7 days produced a decrease in the ratio of activated
mu-calpain in all three fractions in nearly all samples before, during, and after
hypoxia, compared with untreated animals.
Glucocorticoid pretreatment also prevented the increase in
fodrin BDP that occurred in untreated animals during
hypoxia and short-term recovery, indicating impairment of
calpain activation.