Differential enzymatic behaviour of single proximal segments of the superficial and juxtamedullary nephron. I. Alkaline phosphatase, (Mg++) ATPase and Na+K+) ATPase

Renal tubular differentiation in mouse and mouse metanephric culture. II. Na-K-ATPase activity

Sodium-potassium adenosine triphosphatase (Na-K-ATPase) activity was measured by microassay, and the surface density of basolateral membranes was measured morphometrically in postglomerular segments of single tubules isolated from normally developing, intact mouse kidneys and from transfilter metanephric cultures. Proximal tubule Na-K-ATPase activity was 1092 +/- 480 pmol/mm per hour in newborn mice, increasing to 2462 +/- 258 in 1-week-old and 3470 +/- 578 pmol/mm per hour in adult mice. The Na-K-ATPase activity in newborn mice was approximately one-third of the activity in adult mice. Tubular Na-K-ATPase in transfilter metanephric culture was 972 +/- 536 pmol/mm per hour, a mean value almost identical to that in newborn mice. The surface density of basolateral cell membranes was 1.36 +/- 0.60 microns2/microns3 in newborn mice and 1.34 +/- 0.45 microns2/microns3 in 1-week-old mice, increasing to 2.70 +/- 0.98 microns2/microns3 in 4-week-old mice and 2.89 +/- 0.51 microns2/microns3 in adult mice. The surface density of tubular basolateral cell membranes in transfilter metanephric culture was 1.13 +/- 0.51 microns2/microns3, not significantly different from the surface density in newborn mice. The calculated mean surface area of basolateral membranes per unit tubular length was greater in cultures than in newborns, however, because total epithelial volume per unit length was significantly larger in the cultured tubules. Membrane surface area in intact mice increased with age, the surface area per unit length of tubule in adults being 4.6 times the area in newborn animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Histochemical enzyme activity correlated to the structural segmentation of the proximal convoluted tubule in salt-depleted and salt-loaded rat kidneys

In salt-depleted and salt-loaded rat kidneys a study was made of the structural segmentation of the proximal convoluted tubule (PCT) and the histochemical activity of non-specific acid and alkaline phosphatases and succinate dehydrogenase in the same segments. No quantitative structural or segmental alterations were observed, but significant changes in enzyme activity occured. These comprised: 1) A decrease in activity of acid phosphatase in segment 1 and the transitional zone in salt-depleted kidneys, and an increase in enzyme activity in segment 2 in salt-loaded kidneys. 2) a decrease in alkaline phosphatase activity in segment 2 in both salt-depleted and salt-loaded kidneys and 3) a decrease in succinate dehydrogenase activity in segment 2 in salt-depleted kidneys, and an increase in activity in the same segment in salt-loaded kidneys. Thus long-term variation in sodium intake are followed by segment-correlated variations in the activity of acid and alkaline phosphatase and succinate dehydrogenase in the PCT.

A freeze-fracture study of tight junctions in the pars convoluta and pars recta of the renal proximal tubule

The morphology of tight junctions of the renal proximal tubule was studied comparing the pars convoluta and pars recta of rat, golden hamster, rabbit, cat, dog and tupaia. Though some interspecies variations were observed, the convoluted portions of the proximal tubules revealed quite uniformly very leaky tight junctions with mainly 1-2 strands. Along the whole proximal tubule of the rabbit kidney including the pars recta only minor differences of the zonulae occludentes were found. By contrast, the tight junctions of the pars recta in other species were much more elaborate, especially in cat and tupaia, having up to 6 strands and an overall depth of more than 150 nm. The implications of these findings are discussed with special regard to the functional differences between the pars convoluta and pars recta of the proximal tubule.

Measurement of Na K ATPase activity in segments of proximal tubules from superficial and juxtamedullary rat nephrons during antidiuresis

The role of active sodium transport in the partes rectae of subcortical and juxtamedullary proximal nephrons has not yet been established. Recent knowledge of the histotopographical positions of both types of pars recta has now enabled them to be accurately distinguished and isolated from freeze-dried sections. Na K ATPase activity was measured in single dissected tubular segments by an ultramicro method. No significant difference in Na K ATPase activity in the partes rectae from subcortical and juxtamedullary nephrons could be detected.

Isolation of the basal and lateral plasma membranes of rat kidney tubule cells

A method was developed to isolate renal basolateral membranes from cortical kidney tubule cells of single rats. The isolated membrane fraction was characterized by the measurement of marker enzyme activities and by electron microscopy. 1. After centrifugation of crude plasma membranes on a discontinuous sucrose density gradient the basolateral membranes accumulated at a sucrose density of p= 1.14-1.15 g/ml. The yield was 147 mug membrane protein/g kidney wet weight. Protein recovery was 0.1%. 2. (Na+ + K+)-ATPase was enriched 22-fold from the homogenate. The recovery was 2.6%. The (Na+ + K+)/Mg2+-ATPase ratio was 4.1. 3. The contamination by brush borders was small. Alkaline phosphatase was 1.6-fold enriched and 0.2% was recovered. Aminopeptidase was 1-fold enriched with a recovery of 0.1%. The contamination by mitochondria, lysosomes and endoplasmic reticulum was negligible. 4. In electron micrographs the basolateral membranes showed a typical triple layered profile and were characterized by the presence of junctional complexes, gap junctions or tight junctions.

Correlation of enzyme histochemical and structural segmentation in the proximal convoluted tubule of the rat kidney. Enzyme activity compared to the freeze-dried structure of serial-sectioned normal rat nephrons

In the normal rat kidney enzyme histochemical activity was correlated with the structural segmentation of the convoluted part of the proximal tubule, as seen in freeze-dried sections. Serial sections were employed for alternate morphological and enzyme histochemical studies. The tubules were investigated for activity of the following enzymes: 1) non-specific acid phosphatases, 2) non-specific alkaline phosphatases, 3) succinate dehydrogenase and 4) non-specific esterases. Close to the urinary pole acid phosphatase activity was slight in all instances, whilst in the first and second segment a gradual increase in tubular cells with heavy enzyme activity was seen. All tubular cells at the urinary pole showed heavy alkaline phosphatase activity, but there was a gradual increase of cells showing slight enzyme activity in the first and second segments. Succinate dehydrogenase activity was constantly heavy at the urinary pole, and there was a gradual decrease in these cells with heavy enzyme activity along the course of the first and second segments. The pattern of tubular enzyme activity for these three enzymes was independent of the nephron level in the renal cortex. The non-specific esterase activity was, in comparison, uniform throughout the length of the proximal tubule in nephrons from all levels of the renal cortex. This combined enzyme histochemical and morphological investigation demonstrates conclusively that there is a close correlation between structural segmentation and the pattern of enzyme activity of non-specific acid and alkaline phosphatases and succinate dehydrogenase in the proximal convoluted tubule of normal rat kidney.

A comparison of D-inositol 1:2-cyclic phosphate 2-phosphohydrolase with other phosphodiesterases of kidney

1. The ability to hydrolyse various phosphodiesterase substrates was examined in subcellular fractions of rat kidney and in serial slices of the kidneys of mouse, rat, guinea pig and ox cut from the cortex perimeter inwards. 2. d-Inositol 1:2-cyclic phosphate 2-phosphohydrolase could be clearly distinguished from phosphodiesterases which hydrolyse 2':3'- and 3':5'-cyclic AMP and p-nitrophenyl thymidine 5'-phosphate (phosphodiesterase I). The hydrolysis of sn-glycero-3-phosphorylcholine showed a distribution identical with that of particle-bound d-inositol 1:2-cyclic phosphate 2-phosphodiesterase, but there was a 30-fold difference in the ratio of enzyme activities between the rat and guinea pig. 3. In rat and mouse kidney, d-inositol 1:2-cyclic phosphate 2-phosphohydrolase is virtually all membrane bound and in the outer cortex, whereas in guinea-pig kidney the enzyme is almost entirely soluble and located throughout the kidney tissue. Some properties of the soluble enzyme are described. 4. Distribution and histochemical studies indicated that in the rat and mouse, phosphodiesterase I is associated with the brush borders of the straight portion (pars recta) of the proximal tubule, whereas inositol 1:2-cyclic phosphate 2-phosphohydrolase and probably glycerylphosphorylcholine diesterase are associated with the brush borders of the convoluted part of the tubule (pars convoluta).