E. I. Shakhmatova

AVP-independent high osmotic water permeability of frog urinary bladder and autacoids

Abstract In the isolated frog urinary bladder a 20- to 50-fold increase of the osmotic water permeability has been revealed in the absence of arginine vasopressin (AVP) as a result of several successive changes of the serosal Ringer solution. This increase of the osmotic water permeability was of the same magnitude as that of the effect of 1 nM AVP. Similarly to the effect of AVP, the amount of adenosine 3′,5′-cyclic monophosphate (cAMP) in the cells rose, and aggregates of intramembraneous particles were formed in the apical plasma membrane of granular cells (as shown by the freeze-fracture method). Immunocytochemical studies using anti-actin monoclonal antibodies indicated depolymerization of F-actin following the AVP-independent change in water permeability. It was possible to decrease the high level of osmotic permeability to the initial level if 10 µl/ml of frog blood serum or a lipid extract of this blood serum, or 1 µM arachidonic acid or 1 nM prostaglandin E2 was added to the serosal Ringer solution. The rapid restoration of the osmotic water impermeability of the epithelium after the AVP- evoked effect was achieved by the addition to the serosal Ringer solution of Ringer solution in which intact frog urinary bladders had been previously incubated for 1 h. The data obtained indicate that the maintenance of the impermeability to water of the osmoregulating epithelium and the restoration of the initial low level of the osmotic permeability after the effect of AVP are due to participation of prostaglandin E2 and other autacoids as well as, probably, some physiologically active substances of a lipid nature that are present in the blood serum.

PROSTAGLANDIN-DEPENDENT OSMOTIC WATER PERMEABILITY OF THE FROG AND TROUT URINARY BLADDER

Washout of autacoids from serosal Ringer solution, using a repeated change of the solution of the frog and trout urinary bladder, was accompanied by a pronounced rise in the osmotic water permeability: the water transport in the frog rose from 0.05 +/- 0.02 to 1.21 +/- 0.26 microliter min-1.cm-2, in the trout, from 0.041 +/- 0.011 to 0.26 +/- 0.034 microliter min-1.cm-2. Such an increase in the osmotic water permeability in the trout and frog urinary bladder occurred in the background of a decrease in the prostaglandin E2 concentration in the serosal Ringer solution. This permeability increase was accompanied by the formation of aggregates of intramembranous particles in the apical plasma membrane of the trout and frog urinary bladder. A decrease in the osmotic water permeability was achieved by the addition to the serosal Ringer solution of 10-8 M prostaglandin. Experiments on the frog urinary bladder have shown that prostaglandins E1, I2 and F2 alpha also decrease the osmotic water permeability. Vasotocin increased the osmotic water permeability in the frog urinary bladder but did not affect the osmotic water permeability of the trout urinary bladder. The data obtained indicates a role of the endogenous prostaglandin production in maintaining the low osmotic water permeability in the frog and trout urinary bladder. A suggestion is made that in the vertebrate evolution, colonisation of the fresh-water was connected with the maintenance of the low osmotic water permeability via participation of prostaglandins, whereas the vasotocin hydroosmotic effect developed in the vertebrate evolution later and provided for the possibility of the water absorption, osmotic homeostasis and animal migration from fresh-water to the land.

Does the gradual hydroosmotic response to antidiuretic hormone depend on intracellular cAMP accumulation or on the formation of intramembrane particle aggregates

In experiments on frog urinary bladder the mechanisms behind the gradual development of a hydroosmotic reaction to antidiuretic hormone (ADH) were investigated. It was suggested that the velocity of hydroosmotic reaction may be limited by (a) formation and insertion of particle aggregates into the apical membrane or (b) by velocity of cAMP formation. The urinary bladders were exposed to 23 nM ADH for different times (from 1 to 20 min) and water flow was measured over a period of 40 min. It was found that the value of the full hydroosmotic response increased progressively with the time of exposure to the hormone; however, the enhancement of water flow was equal during each time interval before reaching the reaction maximum. A direct correlation between the value of ADH-stimulated water flow, cAMP content in bladder tissue and frequency of particle aggregates in the granular cell apical membrane was observed. The content of cAMP in ADH-treated bladders was higher by 80% in the absence than in the presence of an osmotic gradient. Pretreatment of urinary bladders with 50 μM cyclic nucleotide phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine, significantly accelerated the development of the hydroosmotic reaction and increased the magnitude of water flow in comparison with the effect of ADH only. No changes in cyclic AMP phosphodiesterase activity were found in the urinary bladder homogenates under the action of ADH, so it seems likely that accumulation of cAMP depends only on the increase of adenylate cyclase activity. The data obtained allow one to conclude that the gradual hydroosmotic response to ADH depends on the accumulation of cAMP, which may be considered as the main limiting factor of the velocity of the hydroosmotic reaction.

Vasopressin V1-antagonist increases the hydroosmotic response to arginine vasopressin in frog urinary bladder

V1-antagonist, [Mca1, D-Phe2, Sar7] arginine vasopressin, at a concentration 0.5 nM to 5 nM increased hydroosmotic effect of 5 nM arginine vasopressin in frog urinary bladder. 1 nM V1-antagonist [Mca1,O-Me-Tyr2] arginine vasopressin does not changed hydroosmotic effect of 0.1 mM dibutyryl cAMP. We suggest that — both V1- and V2-receptors are present on epithelial cells of frog urinary bladder and that V1-receptors are involved in the modulation or the hydroosmotic effect of arginine vasopressin — mediated by V2-receptors.

The influence of amlodipine and verapamil on ion and water transport in the nephron, skin and urinary bladder of amphibians

1. The addition of amlodipine or verapamil into the lumen of the newt distal tubule led to the decrease of reabsorption of Na, Cl, Ca and of fluid. 2. The application of amlodipine to the outside of the frog skin caused large increases in potential difference (PD) and short circuit (SCC) similar to what is seen with Co2+. If both amlodipine and Co2+ were applied simultaneously to the outer surface the increases in PD and SCC were additive. 3. Verapamil added to the outer surface of the skin caused a reduction in PD which could be overcome by subsequent addition of amlodipine. 4. After addition of amlodipine to serosal or mucosal surfaces of the frog urinary bladder, the ability of vasopressin to increase osmotic permeability was markedly attenuated. 5. It is likely that the calcium channel blockers used here not only affect intracellular calcium levels by inhibiting entry through calcium channels, but they may also alter calcium dependent processes within the plasma membranes which modulate sodium transfer across epithelia.

Effect of diuretics on the secretion and reabsorption of ions in the kidney of marine teleosts

Abstract 1. 1. Black sculpine with partly aglomerular kidneys from the Barents Sea and black sculpine with glomerular kidneys from the White Sea as well as scorpion fish and mullet from the Black Sea were injected intramuscularly with Lasix, Edecrin, Brinaldix and Diamox. The kidneys of the different species of these fish showed wide variations in their reactions to the injection of diuretics. 2. 2. Following injection of Lasix, Edecrin and Brinaldix, a significant increase in the Na concentration of the urine from black sculpine and mullet was observed, associated with a decrease in Mg concentration in the former and with a sharp increase in chloride concentration in the latter. 3. 3. In experiments performed on black sculpine after simultaneous injection with diuretics and sodium sulphate it was found that diuretics while inhibiting Na reabsorption do not affect sulphate secretion. 4. 4. Lasix, Edecrin and Brinaldix seem to affect primarily Na reabsorption, while the change in the urinary concentration and excretion of other ions depends on the interrelationship between the tubular transport of Na and these ions.

Comparative study of the concentrating mechanism in the kidney of the big gerbil (Rhombomys opimus L.) and the water vole (Arvicola terrestris L.)

Abstract 1. 1. Rodents of the species studied are able to produce a hypoosmotic urine at water diuresis; the urine to plasma osmotic concentration ratio under dehydration in the water vole is 3.8 ± 0.3, in the albino rat—7.0 ± 0.2, and in the big gerbil—12.7 ± 0.9. 2. 2. Microanatomical data agree with the hypothesis of the countercurrent multiplication. 3. 3. The sodium and urea content, under dehydration, increases in the renal papilla of the big gerbil and the water vole as well; the level of potassium, calcium and magnesium remains unchanged. The papilla to cortex gradient of sodium and urea concentrations in the desert rodent is significantly higher than in the vole. 4. 4. Both in the big gerbil and the water vole, the highest succinate dehydrogenase activity is characteristic of tubules of the cortex and the outer medulla but it is not observed in tubular cells of the papilla; a high level of the lactate dehydrogenase activity is also found in the renal papilla structures. The increase of the ability to produce a hyperosmotic urine does not depend on a change of the cellular energetic metabolism type. 5. 5. The adaptive evolution of the renal concentrating ability in water-loving and desert rodents was followed by the change of the Henles loop length and by the modification of some medullar interstitial structures.

The role of the kidneys in the regulation of osmolality and concentrations of cations in the blood serum in hyperglycemia

The role of the kidneys in the restoration of osmotic and ionic homeostasis during persistent hyperosmia caused by hyperglycemia was analyzed. The study was performed in children with diabetes with a disease duration of five months to 17 years. The physical and chemical parameters of their blood serum (such as the osmolality and the concentrations of Na, K, Ca, and Mg) were within standard ranges. Hyperglycemia was shown to be accompanied by decreased concentrations of sodium (r = −0.791, p < 0.01) and magnesium (p < 0.001) in the blood serum. The calculated clearance of sodium-free water indicates that the compensatory reaction is based on greater water reabsorption with increased diuresis. The regulation of water-salt balance keeps the serum potassium and calcium at the levels of the control group. The results indicate that the stability of the cell volume is the predominant aim of the human regulatory system and that increased renal reabsorption of sodium-free water is a physiological compensatory mechanism in hyperglycemia.

Volume and ion regulating renal functions in the big gerbil (Rhombomys opimus L.) and the water vole (Arvicola terrestris L.)

1. After iso-osmotic salt loading (1% NaCl, 1.25% KCl, 0.75% MgCl2 solutions, each load making up 5% body weight) the water voles excreted 66.2% sodium, 84.4% potassium, 18.8% magnesium over a 4 hr period. The big gerbil excreted 20%, 58.9% and 7.1% respectively over the same period. The volume of the water excreted was greater in the case of the water vole. 2. There were no considerable changes in plasma ion concentration in rodents of the species studied after salt loading. 3. The gerbils and water voles had no significant changes in the renal cortex electrolyte concentrations as a result of isotonic salt loads. The highest sodium cortico-papillar gradient was found in the gerbils when experimenting with the isotonic NaCl loading. It was somewhat lower with the KCl load, and significantly lower with water and MgCl2 loads. 4. Under the same experimental conditions, no major changes in the papilla sodium concentration were found in the water voles. 5. The concentrations of potassium, calcium and magnesium were practically alike in all zones of the renal tissue of both rodent species, ion loads producing no effect. 6. The comparison of the renal volume and ion regulating function in rodents with different urine osmotic concentration systems proves the independent existence of renal functions. The greater rate of renal fluid and ion excretion in the water voles is coupled with less specific ion regulation.

Hyaluronidase increases the osmotic resistance of frog urinary bladder

Hyaluronidase (30 U/ml) added from the mucosal side of the frog urinary bladder (pH 5.4, 25°C) is shown to increase the permeability of its wall for water and to shorten fibrillary structures of the apical glycocalyx. The hyaluronidase-mediated increase in osmotic permeability is smaller, and occurs later, than that produced by arginine vasopressin.