Reabsorption and accumulation of α-amino-iso-butyric acid in the nephridia of Sabella pavonina Sa vigny (Annelida polychaeta)

• 1.l. High amino acid concentrations were found in the anterior coelomic fluid of a Polychaeta (Sabella pavonina Savigny).
• 2.2. The concentrations being much higher in the fluid which penetrates the nephrostomia into the nephridia lumen than in the final urine indicates that the nephridia reabsorbs large amounts of amino acids.
• 3.3. Nephridial perfusion experiments showed that an amino acid analogue (α-amino-iso-butyric acid, AIB) is transported by the nephidia.
• 4.4. The transport took place across the nephridial wall owing to the presence of a carrier-mediated transport system and a diffusion system.
• 5.5. For the carrier-mediated transport, the V_max was 0.234 ± 0.025 nmol·min⁻ and the K_m 3.715 ± 0.315mmol·l⁻.
• 6.6. AIB accumulated in the nephridial cells up to a maximum rate of 01.17 nmol·min⁻.
• 7.7. Intracellular accumulation stopped increasing when the V_max for reabsorption was reached.
• 8.8. These results indicate that the carrier-mediated transport of AIB is located at the apical membrane of the nephridial cell, and that AIB transport by simple diffusion takes place through the paracellular pathway.

     

Carbohydrate transport in polychaeta: Reabsorption and accumulation of maltose by the nephridia of Sabella pavonina S

• 1.1. The glucose and maltose concentrations measured in the thoracic coelomic fluid of Sabella were respectively 0.05 and 0.15mg/ml.
• 2.2. Maltose transport was observed to be carrier-mediated in the nephridial wall, with a V_max of 0.03 nmol/min and a K_m of 0.24 mmol/l.
• 3.3. The accumulation rate of maltose in the nephridia was proportional to its reabsorption rate, and exhibited no plateau.

     

Effects of photoperiod on sodium flux in Corbicula fluminea (Mollusca:Bivalvia)

• 1.1. A significant diurnal rhythm of net sodium flux was demonstrated in the freshwater clam Corbicula fluminea entrained to either a 12L:12D or 24L photoperiod.
• 2.2. Highest net flux occurred during the dark hours on 12L: 12D. The overall mean net flux over 24 hr was not significantly different from a steady state condition.
• 3.3. Net flux values of clams on a 24L photoperiod were negative and significantly lower than the net flux on a 12L:12D photoperiod.
• 4.4. The 12L: 12D net sodium flux rhythm pattern is similar to rhythmic patterns of other physiological processes in another freshwater clam.

     

Sodium-dependence of amino acid transport by the nephridia of Sabella pavonina (annelida,polychaeta)

• 1.1. In the absence of sodium, the reabsorption rate of amino acid α-aminoisobutyric acid (AIB) by the nephridia of Sabella pavonina is reduced to 20% and the AIB accumulation in the cells is reduced to 10%. These results suggest the presence of sodium-dependant processes.
• 2.2. The observed processes are reversible when control conditions are re-established.
• 3.3. A minimum of 17mEq/l Na⁺ is required to restore the normal reabsorption rate.
• 4.4. The addition ofamiloride (10⁻³⁵ M) decreases the reabsorption rate, but to a lesser extent than the absence of sodium.

     

Preliminary studies on the characteristics of phenylalanine and β-methyl-glucoside transport in the tench intestine in vitro

• 1.1. The unidirectional transepithelial fluxes of L-phenylalanine, β-methyl-D-glucoside and sodium ions across emusculated sheets of tench mid-intestine were determined in flux chambers.
• 2.2. No net sodium flux was detectable, but phenylalanine was preferentially transferred from the mucosal to the serosal fluid.
• 3.3. There was also a net movement of β-methyl-glucoside towards the serosal medium, but it was much smaller than that of phenylalanine.
• 4.4. This transport was accompanied by an accumulation of each substrate from the mucosal medium into the tissue to a similar level and against a concentration gradient.
• 5.5. The poor transfer of the monosaccharide into the serosal medium could therefore be attributed to a low permeability of the baso-lateral membrane of the enterocyte for this substance.
• 6.6. The influx of L-phenylalanine and of β-methyl-d-glucoside into the epithelial cells of tench midintestine was examined by incubating slices of emusculated intestine in radioactively-labelled solutions of the substrate for 2 min.
• 7.7. The steady-state uptake was assessed after similar incubations lasting 45 min.
• 8.8. Phenylalanine influx obeys the Michaelis-Menten equation with a K_m of 2.9 mM and is dependent on the presence of sodium ions in the incubation medium.
• 9.9. β-Methyl-glucoside influx reveals the same characteristics with a K_m of 2.0 mM but a considerably lower V_max; in addition, it is inhibited by galactose.
• 10.10. The influx of both substrates is reduced by harmaline, which also inhibits the uptake of radioactive sodium by this preparation.
• 11.11. The steady-state uptake of β-methyl-glucoside is also inhibited by ouabain and by 2.4-dinitrophenol.
• 12.12. These results suggest that the mechanisms for sodium-dependent influx of monosaccharides and neutral amino-acids in the tench intestine are similar to those found in mammalian tissues.
• 13.13. The principal difference appears to involve the release of monosaccharides across the baso-lateral membrane of the enterocyte.

     

An in vitro study of short-chain fatty acid concentrations,production and absorption in pig (Sus scrofa) colon

• 1.1. Short-chain fatty acid concentration was 180mmol/l in the proximal colon and decreased to 108 mmol/l in the rectum.
• 2.2. Fermentation in chymus from different regions of the colon, showed the pattern of end products to reflect the substrate and not the site of the colon.
• 3.3. Isolated mucosa from proximal and distal colon had electroneutral sodium absorption of 4.8 ± 0.2 and 2.9 ± 0.8 μeq/cm² hr in bicarbonate free media, which was abolished in the absence of chloride.
• 4.4. Electroneutral sodium absorption was enhanced by short-chain fatty acids in the proximal colon and could be described by Michaelis-Menten kinetics with K_m 2.0–11 mmol/l and J_m 1.6–3.6μeq/cm² hr. In the distal colon the stimulation was smaller and propionate even inhibited sodium absorption.
• 5.5. Butyrate was absorbed in the proximal colon, whereas acetate and propionate, and butyrate in the distal colon had a flux ratio of one.
• 6.6. Amiloride (5 mmol/l) inhibited sodium absorption and net butyrate absorption.

     

The role of extracellular sodium in isosmotic intracellular regulation in the respiratory tree of Holothuria glaberrima

• 1.1. Respiratory trees of Holothuria glaberrima exposed to solutions in which sodium has been replaced by choline, Tris pH 6.1, Tris pH 8.0 or lithium show a net loss of intracellular water, potassium, sodium and chloride. Intracellular content of neutral orgainc osmotic effectors remains unmodified.
• 2.2. Extracellular lithium and Tris pH 8.0 decrease intracellular potassium concentration to half that in sodium, choline and Tris pH 6.1. Intracellular sodium concentration falls markedly while that of chloride falls moderately in sodium-free solutions. Sodium substitutes appear to enter the cells.
• 3.3. A model based on Donnan considerations accounts for the patterns of ion and water distribution.

     

Fluxes of dissolved amino acids between sea water and Echinaster

• 1.1. Measurement of free amino acid (primary amine) influx and efflux into the starfish, Echinaster, were accomplished utilizing improved methods of sea water purification and analysis.
• 2.2. Specimens placed in amino acid depleted sea water (5 × 10⁻⁸ M) demonstrated net release as measured with the fluorescamine method. Similarly, specimens placed in the same water to which amino acid mixtures had been reintroduced to normal levels demonstrated net uptake.
• 3.3. A mathematical model indicated an equilibrium amino acid concentration (when influx equals efflux) of 5.26 × 10⁻⁷ M, or about one fourth the level of natural sea water.
• 4.4. Since at normal environmental levels (20.65 × 10⁻⁷ M) net flux is inward by a ratio of nearly 4-1, it is concluded that the previous suggestions of some workers that such would not be the case for marine invertebrates are no longer valid.
• 5.5. The net uptake of amino acid from environmental levels would account for 5.67% of the measured total respiration if all were being metabolized.
• 6.6. This figure appears to be in line with the previously developed hypothesis that the epidermis largely obtains its nutrition directly from the environment. However, the real benefit of the uptake mechanism may be to prevent loss of the body amino acid pools.

     

Sodium balance in adult atlantic salmon (Salmo salar L.) during migration into neutral and acid fresh water

• 1.1. In sea-water, adult salmon (S. salar) exchange an average of 12.6% of total body sodium/hr.
• 2.2. Following transfer to fresh water sodium uptake follows Michaelis-Menton kinetics. F_max = 2.40 mmol Na/1 ECF/hr, K_m = 0.26 mmol Na/1. The uptake system is fully activated immediately following transfer to fresh water.
• 3.3. Post smolts adapted to sea-water for 3 months take up sodium at only one third of the rate of adult fish following return to fresh water.
• 4.4. The concentration of prolactin in the plasma is low in sea-water adapted fish and does not rise during the first 8 hr in fresh water.
• 5.5. At pH 5 sodium uptake is reduced by almost 90%, even in the absence of aluminium, but recovers immediately on return to neutral water.
• 6.6. At pH 5 and 20 μmol Al/1 there is little further effect on sodium uptake but after 6 hr in aluminium the inhibition of sodium uptake continues after return to neutral aluminium fresh water and uptake is only 50% of normal 24 hr later.

     

Anuran amphibia which are not acclimable to high salt,tolerate high plasma urea

• 1.1. The capacity of five anuran Amphibians (Bufo viridis B. regularis, Rana ridibunda, Hyla arborea and Pelobates syriacus) to acclimate to NaCl and urea solutions was investigated.
• 2.2. All species could be acclimated to relatively high concentrations of urea solutions, while only Bufo viridis and Hyla arborea could be acclimated to 500 mOsm/kg or higher NaCl solutions.
• 3.3. The plasma urea concentration in B. viridis and H. arborea was elevated to levels over 140 mmol/1.
• 4.4. The sum of plasma sodium and chloride concentrations did not increase over 400 mmol/l in any species.
• 5.5. Urine osmolality, which was normally low, increased, but never exceeded the plasma osmolality.
• 6.6. In the urea acclimation conditions, urine electrolytes diminished, similarly in all species in this study.
• 7.7. It is concluded that anuran Amphibians can tolerate high plasma urea concentrations, but only those species which can elevate it, either through retention or net synthesis, can be acclimated to high salt solutions.

     

Interrelationship between metabolism of tritiated water, 22sodium and dry matter intake by beef cattle consuming wheat straw and poultry litter in free choice

• 1.1. Metabolism of tritiated water and ²²sodium was studied in six beef cows under Mediterranean summer conditions in order to find whether the turnover of these tracers can be used to evaluate pasture intake.
• 2.2. The diet of the cows included ad libitum access to two components which were given separately in different troughs: one was poultry litter and the other was wheat straw, to simulate the dry pasture.
• 3.3. Voluntary daily dry matter intake (111 g/kg^0.75) was unexpectedly high considering the low digestibility of the feed.
• 4.4. The assumptions of constant ratios of water intake to water turnover and of dry matter intake to water intake were confirmed. Consequently, dry matter intake was determined accurately from water turnover measurements.
• 5.5. Sodium intake was practically equal to sodium turnover and most of the sodium secreted in feces was of endogenous origin.
• 6.6. Pasture intake can be predicted from sodium turnover once the concentration in feed and water consumed is known.

     

The effect of ovine prolactin on sodium and water transport across the intestine of the fowl (Gallus domesticus)

• 1.1. The effects of ovine prolactin on sodium and water transport across the intestine of 9-day old cockerels were studied by an in vitro everted gut sac technique and by an in vivo balance technique.
• 2.2. Prolactin was found to reduce sodium and water transport across the jejunum and the rectum. AVP was ineffective.
• 3.3. Plasma sodium levels tended to decrease in prolactin treated birds.
• 4.4. It is suggested that the action of prolactin on intestinal salt and water transport is important in maintaining electrolyte homeostasis.

     

Modulation of active potassium transport by aldosterone

• 1.1. The role of aldosterone on active potassium transport across lizard colon under voltage-clamped conditions has been investigated.
• 2.2. Control colons exhibited no net potassium flux (J^k_net) despite of the existence of active opposite unidi ectional fluxes.
• 3.3. An important net secretory potassium flux was found in short-circuited aldosterone-stimulated colons.
• 4.4. Mucosal amiloride did not change (J^k_net) either in control or aldosterone-stimulated colons.
• 5.5. Luminal barium alters K ⁺ transport in a manner consistent with the presence of barium-sensitive conductances at the apical membrane of both control and aldosterone-treated colons.
• 6.6. The effects of ouabain and barium on control and aldosterone-induced potassium flows were consistent with a model involving basolateral uptake by an Na ⁺-K ⁺-ATPase and conductive exit across the apical membrane.
• 7.7. The stimulatory effect of aldosterone on potassium secretion is associated with parallel increases of both basolateral K ⁺ entry and the apical conductive pathway.

     

Uptake of inorganic ions from the maternal circulation during development of the embryo of a viviparous lizard,Sphenomorphus quoyii

• 1.1. Inorganic ion content of developing follicles and of whole eggs and separated embryos and yolk sacs of the viviparous lizard, Sphenomorphus quoyii has been measured.
• 2.2. There is a net increase in calcium, sodium and potassium in whole eggs during gestation. Magnesium and phosphorus content remains constant.
• 3.3. The additional ions are incorporated into the developing embryo.
• 4.4. Calcium content of the yolk is compared with that of the fowl and other species of reptile.

     

Functional maturation of the salt gland of the goose

• 1.1. Experiments were carried out to determine the influence of age on salt gland secretion in the domestic goose.
• 2.2. Oral or i.v. loading of hypertonic NaCl evoked a rapid secretory response in geese 6–14 weeks of age.
• 3.3. A significantly smaller fraction of the salt load was secreted by older birds (2.2 kg and above) than by younger birds (< 2.2 kg).
• 4.4. The maximum volume collected and the maximum sodium concentration during an 80 min observation period did not differ over a range of < 1 kg to > 4 kg in body weight.
• 5.5. The maximum volume and sodium concentration/kg of body weight decreased significantly as the birds aged.
• 6.6. A greater fraction of the administered water load was secreted by the salt gland at any time period compared to the fraction of the salt load secreted, indicating substantial cloacal excretion of the salt load.

     

NADPH/NADP ratio could regulate the glyoxylate cycle in Tetrahymena pyriformis

• 1.1. The glyoxylic acid cycle pathway could be regulated through the modulation of the isocitrate dehydrogenase-NADP activity. This enzyme is inhibited by NADPH.
• 2.2. The effect on the glyoxylate cycle flux of variations in the rate of the NADPH-consuming pathways has been studied.
• 3.3. Increase in the rate of NADPH-consuming activity by addition of H₂O₂ produces inhibition of the glyoxylate cycle and decrease in the NADPH/NADP ratio.
• 4.4. These results suggest that the glyoxylate flux in Tetrahymena could be modulated by regulation of NADP-dependent isocitrate dehydrogenase by the NADPH/NADP ratio.

     

Nitrogenous compounds in the excreta of the germfree snail Biomphalaria glabrata (mollusca: Planorbidae)

• 1.1. Nitrogen excretion of germfree snails kept in sterile saline solution during 14 days consists mainly of ammonia and urea in approximately equal amounts.
• 2.2. Uric acid is excreted intermittently being accumulated in snail nephridia.

     

Changes in high-energy phosphate metabolism in the water scorpion,Ranatra chinensis,under cold water-warm water stress

• 1.1. To evaluate changes in high-energy phosphate metabolism in the water scorpion (Ranatra chinensis) under restraint and cold water-warm water stresses, in vivo [³¹P]NMR spectra were obtained.
• 2.2. Under restraint stress, arginine phosphate (Arg-P) decreased by 10% after 1 hr and remained at that level thereafter, while β-ATP showed negligible changes over 6 hr.
• 3.3. As the water temperature gradually increased or decreased, the relative concentration of Arg-P decreased due to enzyme regulation.
• 4.4. Repeated cold water-warm water stress, which consisted of repeated 15 min exposures to cold water (5°C) followed by 15 min exposures to warm water (30°C) caused distinct decreases in Arg-P and β-ATP concentration. These decreases were dependent on the frequency of exposure.
• 5.5. Phosphomonoesters (PME) increased not only with restraint stress but also with cold water-warm water stress.
• 6.6. The effect of cold water-warm water stress on high-energy phosphate metabolism was greater than that of restraint stress.

     

An alkaline phosphatase from Thermus sp strain Rt41A

• 1.1. A thermostable orthophosphoric monoester phosphohydrolase (EC 3.1.3.1) from Thermus sp strain Rt41A has been purified 400-fold to give a specific activity of 25 U/mg at 60°C in IM diethanolamine (pH 11.1).
• 2.2. The enzyme has a M_r of 160,000 and is trimeric.
• 3.3. The half-life of the enzyme is 5 min at 85°C.
• 4.4. The enzyme has a wide specificity for a number of phosphate monoesters.
• 5.5. The H_m of the enzyme is pH dependent, so the pH optimum of the enzyme is affected by the substrate concentration.
• 6.6. The enzyme is inhibited 50% by 20 mM Ca²⁺ or Mg²⁺.
• 7.7. The K_i for phosphate, EDTA-di sodium salt and arsenate (in 1 M diethanolamine, pH 11.1) is approx 1.2, 1.6 and 4mM respectively.
• 8.8. Urea (200 mM) is not inhibitory.

     

Adaptations of Crocodylus acutus and Alligator for life in saline water

• 1.1. American crocodiles (C. acutus) weighing less than 200 g are unable to grow when kept in 35 ppt sea water in the laboratory. Yet paradoxically there are some highly saline areas in south Florida where rapid growth occurs. It is possible that these conflicting observations can be reconciled by behavioral osmoregulation of young crocodiles.
• 2.2. Hatching occurs during the rainy season and small crocodiles may drink from the brackish “lens” available during and after rainfall.
• 3.3. Using a weekly regime of alternating exposure to 35 ppt (6 days) and 4 ppt (12–24 hr), it has been demonstrated that growth of small crocodiles occurs. Feeding takes place primarily when brackish water is available. Salinities as high as 18 ppt were drunk when crocodiles were dehydrated by 15–20% of initial mass.
• 4.4. C. acutus and Alligator have a rather low rate of water efflux in sea water (0.2ml/100g-hr).
• 5.5. Sodium influx in sea water of C. acutus is low, but higher than efflux. Thus there is no evidence yet for a significant role of the lingual salt glands in sodium excretion.
• 6.6. The major adaptations to saline water of hatchling C. acutus are a low intake of sodium, an ability to selectively drink water of lower salinities, and to grow very rapidly (within 3–4 months) to a size much more tolerant of immersion in 35 ppt sea water.