Journals of Gerontology Series A: Biological Sciences and Medical Sciences, Vol 54, Issue 9 B369-B378, Copyright © 1999 by The Gerontological Society of America
Potassium depletion: renal membrane lipid metabolism and Na/H exchanger abundance in aged F344 x BNF1 rats
S Eiam-Ong and S Sabatini
Department of Internal Medicine, Texas Tech University Health Sciences Center, Lubbock, USA.
Potassium depletion (-K) is a common electrolyte abnormality in elderly
humans, occurring after diuretic use or poor oral intake. We hypothesized
that aging would result in an increase in renal membrane lipid metabolism
in both control and -K, and that the Na/H exchanger's protein abundance to
-K would be blunted. Young and senescent non-obese male Fisher 344 x
Brown-Norway F1 rats (F344 x BNF1) were fed either a normal or a
K-deficient diet for 7 days. At 24-h, 32P incorporation was measured for
renal cortical brush-border (BBM) and basolateral membrane (BLM) lipid
metabolism. All -K animals showed a reduction in total body potassium
stores, a fall in plasma aldosterone, a urinary concentrating defect, and
an increase in plasma cholesterol and urine ammonium excretion (p <
.001). In BBM of both age groups, -K increased phosphatidylserine,
sphingomyelin, phosphatidylcholine, and phosphatidylethanolamine
concentrations, but 32P incorporation fell. In BLM of young K-depleted
rats, however, only phosphatidylcholine concentration increased. In the
hypokalemic aged rats, the concentration of all BLM phospholipids rose,
whereas 32P incorporation fell. In both membranes, cholesterol
concentration and the molar ratio of cholesterol to total phospholipid
increased with -K (p < .05). Potassium depletion caused brush-border
membrane NHE-3 protein abundance to rise, but only in the young rats.
Neither NHE-3 nor basolateral NHE-1 protein abundance was affected in aged
animals with - K. These results provide the first evidence, in non-obese
aged rats, that selective age-associated modifications occur in membrane
lipid metabolism and membrane transporter protein abundance during -K. That
aging causes a maladaptive response in brush-border NHE-3 protein
expression may have important implications for elderly humans, particularly
if they are given diuretics and become potassium depleted.
