acid-phosphatase and Potassium-Deficiency

Lysosome formation was induced in cells of the renal medulla by feeding rats on a K+-deficient diet. The role of the endoplasmic reticulum in the production of acid phosphatase, a typical lysosomal enzyme, was examined. Lysosomal and microsomal fractions were prepared for study by differential centrifugation of homogenates of renal papilla and inner stripe of red medulla. Acid phosphatase activity in the microsomal fraction was distinguished from the activity in the lysosomal fraction in normal tissue by differences in pH optima, tartrate inhibition, distribution of multiple forms after polyacrylamide-gel electrophoresis and detergent-sensitivity. During progressive K+ depletion, acid phosphatase activity in both microsomal and lysosomal fractions of the tissue increased 3-fold. In the lysosomes, K+ depletion was associated with the appearance of a new band of acid phosphatase. The neuraminidase-sensitivity of this band on polyacrylamide-gel electrophoresis indicated that the enzyme protein had been modified by the addition of sialic acid residues. K+ depletion also altered the lysosomal enzyme so that thiol compounds were able to stimulate its activity.

Topics: Acid Phosphatase; Animals; Electrophoresis, Polyacrylamide Gel; In Vitro Techniques; Isoenzymes; Kidney Medulla; Lysosomes; Male; Neuraminidase; Potassium Deficiency; Rats; Rats, Inbred Strains; Subcellular Fractions

The biochemical correlates of droplet formation in renal inner medullary cells of potassium-deficient rats were studied. An increase in the activities of five hydrolytic enzymes typical of lysosomes was associated with an increase in the number and size of droplets observed during progressive potassium depletion. Acid phosphatase activity increased 7-fold whereas beta-glucuronidase, beta-galactosidase, cathepsin, and acid DNase increased 2- to 4-fold in medullary homogenates at 25 days of depletion. Following potassium repletion the activities returned to normal at a rate dependent upon the duration of potassium depletion. The decreases in enzyme activities were associated with a concomitant rapid disappearance of the droplets from medullary cells. Protein synthesis for new droplet enzyme formation was studied by measuring the rate of [14C]leucine incorporation into protein in medullary slices. The rate increased at 1 day of depletion and reached a maximum which was 139 per cent higher than control after 7 days of depletion. In droplets isolated from medullary tissue during progressive potassium depletion the rate of protein labeling with [14C]leucine and acid phosphatase specific activity increased in parallel. When droplet proteins were separated by gel electrophoresis, acid phosphatase activity was detected in a protein band which had been labeled with [14C]leucine, thereby suggesting new enzyme protein formation. The increase in enzyme and protein synthesis and a previously demonstrated increase in phospholipid synthesis and membrane formation indicate that potassium depletion induces specific alterations in renal inner medullary cell metabolism which result in increased lysosome formation.

Topics: Acid Phosphatase; Alkaline Phosphatase; Animals; Cathepsins; Cycloheximide; Deoxyribonucleases; Galactosidases; Glucuronidase; Kidney; Kidney Cortex; Kidney Diseases; Kidney Medulla; Leucine; Lysosomes; Male; Potassium Deficiency; Protein Biosynthesis; Rats

Topics: Acetamides; Acetylesterase; Acid Phosphatase; Adenosine Triphosphatases; Alkaline Phosphatase; Animals; Aspartic Acid; Dihydrolipoamide Dehydrogenase; Electron Transport Complex IV; Glucose-6-Phosphatase; Glucosephosphate Dehydrogenase; Glutamate Dehydrogenase; Histocytochemistry; Isocitrate Dehydrogenase; L-Lactate Dehydrogenase; Liver; Liver Glycogen; Malate Dehydrogenase; Male; Potassium Chloride; Potassium Deficiency; Rats; RNA; Succinate Dehydrogenase

Topics: Acid Phosphatase; Electrons; Histocytochemistry; Kidney; Lysosomes; Microscopy; Microscopy, Electron; Potassium Deficiency; Rats; Research