Abstract
The uneven distribution of Na K ATPase along the renal tubule of the rat has only recently been recognized (1). The resulting unequal distribution of this enzyme in the cortex and medulla (2) is currently an important consideration when renal Na K ATPase activity is assayed (3). Usually, this enzyme is measured in one kidney or in tissue pooled from both kidneys of the experimental animal. To the extent that equal quantities of tissue from each kidney are included in the measurement, the resultant enzyme activity approaches the mean of the enzyme activity of the two kidneys. In fact, equal quantities of tissue from each kidney are rarely obtained, since it is commonly assumed that the specific activity of Na K ATPase is equal in both kidneys. This study was undertaken to test this assumption.
Methods. Male albino Sprague-Dawley rats weighing 180–300 g were maintained on a standard Purina Rat Chow diet with free access to water. Under light ether anesthesia, right and left kidneys were removed in random order and placed in chilled 0.9% saline. After removal of the capsule, each kidney was weighed. Sagittal hemisection of the kidney was performed revealing the boundary between outer (red) medulla and cortex. Samples of each zone were obtained by careful dissection of this boundary. The inner (white) medulla was discarded. Dissection was performed on a filter paper moistened with saline and placed upon a glass petri dish resting on ice. The specific activity of Na K ATPase in whole homogenates of renal cortex and outer medulla of each kidney was determined as previously described (3). A minimum of 20 min after homogenization samples were incubated in a medium at pH 7.8 containing NaCl, 100 mM; KCl, 20 mM, imidazole buffer, 10 mM; MgCl2, 6 mM; and disodium ATP (Sigma Chemical Corp., Grade II), 6 mM. The reaction was begun by addition of MgCl2 and ATP and carried out at 37° for 15 min in a shaking water bath.
Get full access to this article
View all access options for this article.