Micropuncture studies of proximal tubule albumin concentrations in normal and nephrotic rats

Abstract

A B S T R A C T The concentration of serum albumin in proximal tubule fluid of normal rats and animals with aminonucleoside nephrosis was studied using renal micropuncture techniques. Albumin was quantitated by an ultramicrodisc electrophoresis method capable of measuring 3 X 10'" g of albumin, in 10 nl volumes. With this sensitivity., only small samples of tubule fluid were required for analysis. Collectifn times could be kept short, therefore decreasing the opportunity for sample contamination with extraneous serum albumin. The measured mean concentration of albumin in proximal tubule fluid (1 mg/100 ml in females and 0.7 mg/ 100 ml in males) was somewhat lower than values reported by others, but even these values are apt to have been artifactually high as a result of animal preparation and trace contamination of samples during micropuncture. Rats injected with aminonucleoside of puromycin 4 days earlier, showed a significant increase in tubulefluid albumin concentration coincident with a fall in serum albumin concentration and a 43-fold increase in urine albumin concentration. Tubular absorption of albumin was small relative to that of water. Although albumin filtration was significantly increased over that in normal animals, the glomerular basement membrane still served as a highly efficient barrier to albumin transfer.

"Intact nephrons" as the primary origin of proteinuria in chronic renal disease. Study in the rat model of subtotal nephrectomy.

“…The relationship between the sclerosis index and albumin filtration rate, determined for each glomerulus in group IA rats, is demonstrated Our ELISA method detects < 1 ng/ml albumin and provides a slightly more sensitive assay system than the ultramicrodisc gel electrophoresis technique that has been used for the measurement of albumin in tubular fluid (27). In group 1 B rats, which were prepared in a fashion similar to that of group IA rats, we examined the population distribution ofglomeruli with varying degrees of sclerosis index, which were obtained from multiple thin section analyses.…”

Albumin-stimulated DNA synthesis is mediated by Ca2+/PKC as well as EGF receptor-dependent p44/42 MAPK and NF-κB signal pathways in renal proximal tubule cells

“…Accordingly, micropuncture studies revealed that albumin concentrations range from 20 to 30 g/ml in the proximal tubules of rodents. The induction of nephrosis causes up to a 100-fold increase in the albumin concentration prevailing in the proximal tubule (22,27). Therefore, a range of protein concentrations comparable to those used in other studies were chosen.…”

Resolved

“…This process is probably responsible for the enormous variation in tubular lumen albumin concentrations depending on the method of collection. 1,20 Tojo and Endou 21 noted a 50-fold variation for serially collected fractions from the proximal tubular lumen and had to eliminate 75% of their data to obtain a sieving coefficient of 0.0006. In fact, the initial fractions collected indicate an albumin GSC comparable to that obtained by our 2-photon study, but these data were eliminated as it was thought to be the result of plasma contamination.…”