Age-related changes by hypoxia and TRH analogue on synaptic ATPase activities.

Some synaptosomal energy-requiring ATPases were evaluated in the cerebral cortex from 3- and 24-month-old normoxic rats and rats submitted to either mild or severe chronic (4 weeks) intermittent normobaric hypoxia. Furthermore, 4-week treatment with saline or TRH analogue posatireline was performed. The activities of Na+,K(+)-ATPase, low- and high-affinity Ca(2+)-ATPase, and Ca2+,Mg(2+)-ATPase were assayed in synaptosomes and synaptosomal subfractions, namely synaptosomal plasma membranes and synaptic vesicles. With the exception of the high-affinity Ca(2+)-ATPase, aging induced a decrease in the ATPase activities from normoxic rats. The adaptation to chronic intermittent mild hypoxia was characterized by an increase in the activity of Mg(2+)-ATPase in 3-month-old rats, concomitant with a decrease in the activities of: a) Na+,K(+)-ATPase and high-affinity Ca(2+)-ATPase in both 3- and 24-month-old rats, and b) Ca2+,Mg(2+)-ATPase in 3-month-old ones. The TRH analogue posatireline increased the high-affinity Ca(2+)-ATPase in both 3- and 24-month-old hypoxic rats, concomitant with an increase in Mg(2+)-ATPase activity in 24-month-old ones. The adaptation to chronic intermittent severe hypoxia was characterized by a decrease in the activities of: a) Na+,K(+)-ATPase, Ca2+,Mg(2+)-ATPase and high-affinity Ca(2+)-ATPase in both 3- and 24-month-old rats, and b) low-affinity Ca(2+)-ATPase only in 24-month-old ones. The effect on Mg(2+)-ATPase activity was characterized by a decrease in the enzymatic form located in the synaptic plasma membranes, concomitant with an increase in the form located in the synaptic vesicles.(ABSTRACT TRUNCATED AT 250 WORDS)