Na+-K+-ATPase pump function in rat brain synaptosomes is different in males and females

To understand the increased morbidity and mortality associated with acute hyponatremia in young women, we characterized the Na+-K+-adenosinetriphosphtase (ATPase) pump in rat brain synaptosomes to determine if this adaptive mechanism was different between the sexes. Veratridine-stimulated sodium (Na+) uptake was significantly greater (P less than 0.001) in females than in males (8.08 +/- 0.3 vs. 5.56 +/- 0.4 nmol/mg protein), suggesting either an increased rate of Na+ uptake and/or decreased extrusion of Na+ by the Na+-K+-ATPase pump in females. Uptake rate was determined by measuring Na+ transport at 5 s, and it was found to be twice as large in females as in males (1.01 +/- 0.2 vs. 0.46 +/- 0.1 nmol/mg protein). However, in the presence of 2.5 mM ouabain, uptake in both groups were similar, suggesting that the difference was probably due to decreased function of the Na+-K+-ATPase pump in females. Transport evaluation of the Na+-K+-ATPase pump showed ouabain-sensitive K+ uptake in males to be significantly greater (P less than 0.001) than in females (10.53 vs. 4.97 nmol/mg protein), and ouabain-sensitive Na+ uptake in inverted synaptosomes was 70% greater in males (4.00 vs. 2.37 nmol/mg protein). [3H]ouabain binding studies showed maximum binding capacity in males and females to be similar (103 +/- 12 vs. 110 +/- 15 pmol/mg protein), whereas the dissociation constant was significantly (P less than 0.005) greater in males (109 +/- 8 vs. 82 +/- 6 nM).(ABSTRACT TRUNCATED AT 250 WORDS)