The long-term objectives of this proposal include the elucidation of nephronal heterogeneity of transport enzymes, the factors which regulate transport enzymes in each nephron segment and the mechanism by which these factors regulate the transport enzymmes, especially ATPases. An electroneutral H-K-Atpase has been reported to be present in the stomach where it is responsible for H+ secretion. Our preliminary observations indicate that an ATPase, is present in the distal nephron where it may be responsible for K+ reabsorption and/or H+ secretion. The specific aim of this project is to study the regulation of renal tubular K- ATPase in the distal segments of the mammalian nephron by adrenocorticosteroids, plasma K+ and extracellular volume (Na intake). This aim will be pursued by determining K-ATPase activity in distal nephron segments of normal and adrenalectomized rabbits by an ultramicroassay method developed in our laboratory. The effects of different intakes of potassium and sodium and administration of corticosteroids (aldosterone and dexamethasone) on K-ATPase activity in the distal nephron segments will be studied. The relationships between concentrations of K+ and cortocosteroids in the plasma and K-ATPase activity in different nephron segments will then be determined. The kidney plays an inportant role in maintaining the volume and composition of the body fluids. Urine formation is corollary of the primary function of the kidney in regulating the concentration of salts in the body fluids. There are two principal steps involved in the formation of urine: 1) filtration of large amounts of nutrients and salts, but not proteins and cells from blood, through specialized structures called glomeruli, and 2) reabsorption of 100% of filtered nutrients (such as glucose and amino acid) and approximately 99% of salts back into the blood through microscopic structures called tubules which are connected to the glomeruli. It is the second step which is regulated by several hormones (specialized chemicals released into the blood by special organs of the body) and the changes in salt composition of the blood due to a change in our diet. An enzyme protein called Na-K-ATPase is present in the renal tubules and is responsible for reabsorption of salt and nutrients from the filtered tubular fluid back into the blood. Recently, we have discovered that another enzyme called H-K-ATPase is also present in the distal parts of the renal tubule. Our preliminary observations suggest that this H-K-ATPase may be responsible for maintaining normal concentration of potassium in the blood during decreased intake of potassium in our diet.
