AJP - Regulatory, Integrative and Comparative Physiology, Vol 247, Issue 5 850-R855, Copyright © 1984 by American Physiological Society
Kinetic studies of the Na+-K+-ATPase enzyme system in brain and heart of aging rats
L. B. Poole, M. S. Liu and P. W. Landfield
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.
