Protein reabsorption in lake frog’s kidneys during changes in water-salt balance

The aim of the work was to study the reabsorption of proteins in the kidneys of lake frogs (Pelophylax ridibundus) in hypervolemia, dehydration and the action of arginine-vasotocin (AVT), the antidiuretic hormone of amphibians. Methods of immunohistochemistry, confocal microscopy and automated analysis of fluorescent signals were used. The fluorescence of endocytic receptor megalin, injected proteins lysozyme and green fluorescent protein (GFP) in the proximal tubules were analyzed on fixed kidney specimens. The intensity of the signals, the number of fluorescent tubules and endocytic vesicles, and the percentage of colocalization of proteins with megalin were calculated. Dehydration and injections of AVT leads, as a rule, to a decrease in reabsorption parameters. The data were compared with similar effects of hypernatremia, as well as with changes in blood parameters and kidney functions previously demonstrated under analogue experimental conditions. It can be assumed that an increase in the concentrations of osmotically active substances in blood and primary urine, as well as a decrease in the glomerular filtration rate, leads to the decline in protein uptake and rate of intracellular protein transport in proximal tubular cells in frogs.