title: Kinetic studies of the Na+-K+-ATPase enzyme system in brain and heart of aging rats.
abstract: Kinetic analyses of the Na+-K+-adenosine triphosphatase (ATPase) system were performed in brain and heart preparations from young mature (4 mo old) and healthy aged (25 mo old) rats. The K+-activated p-nitrophenylphosphatase (K+-pNPPase) method was used to assess activity of the enzyme system. Ouabain inhibition of K+-pNPPase activity was also examined. A significant age-related decrease in maximal velocity (Vmax) was found in cardiac K+-pNPPase activity, but no changes were seen in the K+ concentration for half-maximal velocity (K0.5). No age differences in Vmax or K0.5 were seen for brain. No differences in ouabain inhibition were found in either brain or heart. In a second experiment, the major component of the age-related decline in cardiac K+-pNPPase activity was found to occur between 5 and 14 mo of age, a period during which plasma thyroxine had previously been found to decline in the same animals. Since peripheral Na+-K+-ATPase activity is partly thyroid hormone dependent, the age-dependent decrease in cardiac enzyme activity appears to be secondary to neuroendocrine changes.
mesh_terms: D009597:4-Nitrophenylphosphatase / Q000378:metabolism; D000375:Aging; D000818:Animals; D001921:Brain / Q000201:enzymology*; D004789:Enzyme Activation / Q000187:drug effects; D007700:Kinetics; D008297:Male; D009206:Myocardium / Q000201:enzymology*; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D011916:Rats, Inbred F344; D000254:Sodium-Potassium-Exchanging ATPase / Q000096:biosynthesis / Q000378:metabolism*; D013974:Thyroxine / Q000097:blood
chemical_list: D010042:Ouabain; D009597:4-Nitrophenylphosphatase; D000254:Sodium-Potassium-Exchanging ATPase; D013974:Thyroxine; D011188:Potassium