SYNAPTOSOMAL NONMITOCHONDRIAL ATPASE ACTIVITIES - AGE-RELATED ALTERATIONS BY CHRONIC NORMOBARIC INTERMITTENT HYPOXIA

In synaptosomes and synaptosomal subfractions (namely, synaptosomal plasma membranes and synaptic vesicles) the age-related alteration in the plasticity of synaptic energy-requiring ATPases (Na+, K+-ATPase, low- and high-amnity Ca2+-ATPase: Mg2+-ATPase and Ca2+, Mg2+-ATPase) were assayed in the cerebral cortex from 3- and 24-month-old normoxic rats and rats subjected to either mild or severe chronic (4 weeks) intermittent normobaric hypoxia. With the exception of the high-affinity Ca2+- ATPase, aging induced a decrease in the ATPase activities from normoxic rats. The adaptation to mild hypoxia was characterized by an increase in the activity of Mg2+-ATPase in 3-month-old rats, concomitant with a decrease in the activities of: (i) Na+, K+-ATPase and high-affinity Ca2+-ATPase in both 3- and 24-month-old rats; and (ii) Ca2+, Mg2+-ATPase in 3-month-old ones. The adaptation to chronic intermittent severe hypoxia was characterized by a decrease in the activities of: (i) Na+, K+-ATPase, Ca2+, Mg2+-ATPase and high-affinity Ca2+-ATPase in both 3- and 24-month-old rats and (ii) low-affinity Ca2+-ATPase only in 24-month-old ones. The effect on Mg2+-ATPase activity was characterized by a decrease in the activity of the enzymatic Form located in the synaptic plasma membranes (involved in ATP hydrolysis to adenosine production), concomitant with an increase in the activity of the form located in the synaptic vesicles (involved in the turnover of transmitters, e.g., glutamate).