Contrast in adenine uptake by chicken and rabbit erythrocytes in vitro

• 1.1. Relative to rabbit erythrocytes, chicken red blood cells exhibit a much greater capacity to utilize [³H]adenine for nucleotide synthesis in vitro, even at 5°C and in the absence of added inorganic phosphate.
• 2.2. This difference is largely due to a higher concentration of phosphoribosylpyrophosphate and greater activity of adenine phosphoribosyltransferase in the avian cells. lli]3. The capacity of avian erythrocytes for utilization of guanine and hypoxanthine is several fold less than that of adenine.
• 3.4. The data are consistent with lower activity for hypoxanthine/guanine phosphoribosyltransferase than for adenine phosphoribosyltransferase in intact chicken erythrocytes.
• 4.5. The results indicate that reutilization of adenine by chicken erythrocytes may be physiologically significant.

     

Regulation of rat-kidney cortex fructose-1,6-bisphosphatase activity. II. Effects of adenine nucleotides

• 1.1. The native rat-kidney cortex Fructose-1,6-bisphosphatase is differentially regulated by adenine nucleotides in the presence of divalent cations.
• 2.2. Binding of AMP and ADP to the enzyme is co-operative. The inhibition by both nucleotides show an uncompetitive mechanism AMP being the most efficient inhibitor.
• 3.3. Mg²⁺ decreases the inhibition produced by AMP and ADP by enhancing their I_0.5 and completely annulates the inhibitory effect of ATP.
• 4.4. In the presence of Mn²⁺ ADP behaves as an inhibitor but no inhibition is evident with AMP, suggesting the existence of different allosteric sites for each nucleotide.

     

Effect of inorganic phosphate on synthesis of 5-phosphoribosyl-1-pyrophosphate in cultured plant cells

• 1.1. Inorganic phosphate (Pi) was absorbed rapidly by suspension-cultured cells of Catharanthus roseus which had previously been cultured in Pi-free Murashige Skoog medium.
• 2.2. The intracellular levels of ATP, ADP and 5-phosphoribosyl-l-pyrophosphate (PRPP) increased markedly during the 24 hr which followed the addition of Pi (1.25mM).
• 3.3. Availability of PRPP in vivo, estimated by the measurement of nucleotide synthesis from [8-¹⁴C]adenine, was also increased by addition of Pi.
• 4.4. Only a 20% increase in the maximum catalytic activity of PRPP synthetase was observed in extracts of cells, prepared 24 hr after addition of Pi.
• 5.5. In contrast to results for mammalian PRPP synthetase, the activity of PRPP synthetase, partially purified from Catharanthus roseus, was inhibited by concentration of Pi greater than 5mM.
• 6.6. The mechanisms involved in the increased availability of PRPP and the synthesis of adenine nucleotides in the plant cells cultured in Pi-containing medium are discussed.

     

Possible involvement of adenylylation in the modification of a 26 kDa protein in rat parotid acinar cells

• 1.1. Adenylylation, a posttranslational modification of proteins, was investigated in saponin-permeabilized acinar cells of the rat parotid gland.
• 2.2. When cells were incubated with [2,8-³H]ATP, several proteins, including a 26 kDa protein in the particulate fraction, were labeled.
• 3.3. Upon incubation of cells with [α-³²P]ATP in the presence of cAMP and 3-isobutyl-lmethylxanthine, ³²P-labeling of the 26 kDa protein was observed.
• 4.4. After treatment with snake venom phosphodiesterase, [³²P]AMP was released from the 26kDa protein. Such release was not observed when cells were labeled with [γ-³²P]ATP.
• 5.5. The ³²P-labeling pattern of proteins with [α-³²P]ATP was clearly different from that with [adenylate-³²P]NAD⁺.
• 6.6. The results suggest that the 26 kDa protein is one of the adenylylation substrates in rat parotid acinar cells.

     

Blood volume recovery in hemorrhaged japanese quail

• 1.1. Blood volume and plasma biochemical changes and feed and water consumption in response to a hemorrhage by phlebotomy of 30% of the calculated total blood volume with and without replacement of blood volume with physiological saline were determined in juvenile male Coturnix coturnix japonica.
• 2.2. Plasma protein and osmolality decreased rapidly posthemorrhage and did not recover by 72 hr posthemorrhage.
• 3.3. Plasma glucose, Na⁺ and K⁺ increased within Ihr postphlebotomy. Plasma Na⁺ returned to nonphlebotomized levels within 6 hr postphlebotomy.
• 4.4. Saline replacement of blood volume resulted in hypervolemia within 3–5 min postphlebotomy.
• 5.5. Phlebotomized quail receiving no saline recovered blood volume to 0 hr (nonphlebotomized) levels within l hr postphlebotomy.

     

Phosphorylation in crayfish (Procambarus clarkii) eggs during hatching

• 1.1.|The high-energy phosphorylation metabolism in crayfish, Procambarus clarkii eggs during brooding and juvenile crayfish after hatching was studied by in vivo³¹P nuclear magnetic resonance (³¹P NMR) spectroscopy.
• 2.2.|Inorganic phosphoric acid (Pi) and adenosine-5′-triphosphate ATP(γ-,α-,β-) were detected in the dark brownish red eggs after oviposition.
• 3.3.|In orange unhatched eggs, only sugar phosphate (SP), Pi and resolved phosphometabolite from ATP were observed.
• 4.4.|Peaks of SP, Pi, arginine phosphate (Arg-P), and ATP (γ,α,β) appeared in larvae of crayfish after hatching (nauplius, zoea and juvenile crayfish).
• 5.5.|The high-energy phosphorylation metabolism changed to an anaerobic condition along with a decrease in the concentration of dissolved oxygen in fresh water.

     

Elasmobranch fish (Scyliorhinus canicula and Raja clavata) muscle AMP deaminase: Substrate specificity and effect of EDTA and adenylate energy charge

• 1.1. The AMP deaminases from skeletal muscles of dogfish and skate were shown to be specific to 5′-AMP. Among several adenine nucleotide analogs, only dAMP was deaminated to an extent lower than 5%.
• 2.2. Similar to vertebrates AMP deaminases, these enzymes were inhibited when incubated in the presence of EDTA solutions.
• 3.3. The activity of the enzymes was regulated by adenylic energy charge variations, depending on the size of the total adenine nucleotide pool.
• 4.4. The shape of the adenylate energy charge response curves of the dogfish and skate muscle AMP deaminases do not distinguish the two enzymes.

     

Apparent low free magnesium levels in blue crab vas deferens determined by 31P NMR

• 1.1. ³¹P NMR examination of blue crab vas deferens reveals an α-β ATP chemical shift differences on average of 9.8 ppm.
• 2.2. This implies a free magnesium concentration well below 100 μM.
• 3.3. Thus crab vas deferens represents a new model for a low free magnesium system.
• 4.4. These results also point to a feature of carcine metabolism not previously recognized.

     

Salinity-dependence of the properties of gill (Na++K+-ATPase in rainbow trout Oncorhynchus mykiss

• 1.1. The expected higher gill (Na⁺+K⁺)-ATPase activity in rainbow trout adapted to brackish water (BW) with respect to fresh water (FW) is accompanied by some changes in the enzyme kinetics while the enzyme sensitivity to ouabain is unaffected
• 2.2. Maximal activation is attained under the optimal conditions of 4 mM ATP, 7.5 mM Mg²⁺, 50 mM Na⁺, 2.5 mM K⁺, pH 7.0 in FW, and 3 mM ATP, 10 mM Mg²⁺, 100 mM Na⁺, 10 mM K⁺, pH 7.5 in BW.
• 3.3. The change of the enzyme activation kinetics by Mg²⁺, ATP, Na⁺ and K⁺ from simple saturation in FW to cooperativity in BW and other habitat-dependent variations including the pH alkaline shift in BW are hypothetically related to an adaptive significance to the different environmental salinity.
• 4.4. Gill total lipids and phospholipids are 30% lower in BW than in FW while their ratio is constant; some differences in gill total lipid fatty acid composition between FW and BW do not significantly affect the unsaturation parameters.

     

A comparison of the effect of alternating current electronarcosis,rectified current electronarcosis and chemical anaesthesia on the blood physiology of the freshwater bream Oreochromis mossambicus (peters)—III. The effect on the plasma electrolytes Ca2+, Na+ and K+ and on the osmotic pressure of the blood

• 1.1. The effects of alternating current electronarcosis, rectified current electronarcosis and chemical anaesthesia (benzocaine hydrochloride) on plasma electrolytes and on the osmotic pressure of the blood of the freshwater bream Oreochromis mossambicus were evaluated.
• 2.2. Plasma Ca²⁺, Na⁺ and K⁺ concentrations and the osmotic pressure of the blood were monitored over a period of 7 days.
• 3.3. The results showed that the different electrolytes respond differently to the different techniques.
• 4.4. Chemical anaesthesia exhibited the least effects on the parameters studied.

     

Metabolic and functional characteristics of erythrocytes from Glycera and Noetia

• 1.1. Annelid and molluscan red blood cells (RBC) may de differentiated metabolically from vertebrate RBC by their increased permeability to substrate, their magnitude of amino acid catabolism and their higher aerobic metabolism.
• 2.2. At 22°C, Glycera and Noetia RBC oxidize glucose and glutamate to CO₂ without accumulation of either d- or l-lactate. By comparison, the oxidation of glutamate by rat and chicken RBC is negligible at this temperature despite its incorporation into the cells.
• 3.3. At 37°C, chicken RBC oxidize glutamate at a rate 4 times greater than at 22°C, with oxygen uptake still lower than that in Noetia RBC at 32°C. At 37°C, rat RBC do not increase their oxidation of glutamate above that at 22°C, but oxygen uptake increases to slightly more than half that of chicken RBC.
• 4.4. Our finclings indicate that RBC of these two invertebrate species have both a higher aerobic metabolism and lower anerobic capacity than vertebrate RBC.
• 5.5. Moreover, the annelid and molluscan RBC have a relatively lower activity of the pentose phosphate (PPO₄) pathway than vertebrate RBC, as evidenced by their higher thermal sensitivity of oxygen uptake and their higher *C₁O₂/*C₆O₂ isotope ratio.

     

Sodium transport in red blood cells of lamprey LAmpetra fluviatilis

• 1.1. Unidirectional Na⁺ influx in lamprey red blood cells was determined using ²²Na as a tracer.
• 2.2. Total Na⁺ uptake and amiloride-inhibitable Na⁺ influx increased in a saturable fashion as a function of external Na⁺ concentration (Na_e).
• 3.3. At 141 mM Na_e, the average value of net Na⁺ influx was 13 ± 1.1 and the amiloride-sensitive Na⁺ influx was 5.3±1.1 mmol/l cells per hr (±SE).
• 4.4. The amiloride-sensitive component of Na⁺ influx was significantly activated by 10⁻⁵ M isoproterenol, by 2 × 10⁻⁵ M DNP, and by cell shrinkage.
• 5.5. Furosemide (1 mM) had no effect on the Na⁺ transport in red cells.
• 6.6. The residual amiloride-insensitive component of Na⁺ transport was a linear function of Na_e in the range of 5–141 mM. This transport seems to be accounted for by simple diffusion.

     

Serum ions concentration and atpase activity in gills,kidney and oesophagus of european sea bass (Dicentrarchus labrax,pisces, perciformes) during acclimation trials to fresh water

• 1.1. Kidney, oesophagus and gill Na⁺-K⁺ ATPase activity and serum Na⁺, K⁺ and Cl⁻ concentrations are evaluated in European sea bass during experimental acclimation to fresh water.
• 2.2. Kidney and oesophagus ATPase increase in low salinity and reach a maximum in fresh water.
• 3.3. Gill ATPase decreases during the acclimation trials and rises again to normal values after a 3-week stay in fresh water.
• 4.4. Na⁺ and K⁺ serum concentrations decrease during the trials and increase back after a 3-week stay in fresh water.
• 5.5. The correlations between enzymatic activities, serum ion concentrations, morphological changes and environmental salinity are discussed.

     

Crayfish retinular cells: Influence of extracellular sodium and calcium upon receptor potential

• 1.1. In crayfish, light stimulation of the retinular cells induces a depolarizing receptor potential.
• 2.2. Experiments were designed to determine the role of Na⁺ and Ca²⁺ on receptor potential during dark And light states.
• 3.3. Depolarization depends on Na⁺ and Ca²⁺ availability to the retinular cell.
• 4.4. Repolarization velocity and response duration depend on extracellular Ca²⁺ availability.
• 5.5. Light adaptation increases receptor potential dependence on calcium and sodium ions.
• 6.6. We analyse these results with respect to other invertebrate photoreceptors.

     

Modulation of the ATP induced [Ca2+]c increase in as-30D hepatoma cells

• 1.1. The regulation of the increase in the cytosolic calcium concentration ([Ca²⁺]c) induced by extracellular ATP in AS-30D hepatoma cells was studied.
• 2.2. Homologous desensitization involving the refilling of intracellular calcium pools and the participation of protein kinase C was found.
• 3.3. Isoproterenol, forskolin and dibutyril-cyclic AMP also induced an increase in [Ca²⁺]c.
• 4.4. Interestingly, synergism was found for isoproterenol or forskolin and ATP.
• 5.5. The results suggest that there are two pathways for mobilizing [Ca²⁺] in AS-30D hepatoma cells; one is activated by ATP receptors and the other by cyclic AMP.

     

The regulation of glucose 6-phosphate dehydrogenase from Dicentrarchus labrax (bass) liver

• 1.1. Kinetic constant values of the reaction catalyzed by bass liver glucose 6-phosphate dehydrogenase show to be modified between 10 and 40°C.
• 2.2. The Arrhenius plot between 10 and 50°C shows two slopes with different activation energies.
• 3.3. These results suggest a regulation of this enzyme by environmental temperature.
• 4.4. Kinetics of ATP inhibition were examined between pH 6.2 and 7.8: patterns and K_i values obtained are affected by the pH variation.
• 5.5. NADH is an effective inhibitor of bass glucose 6-phosphate dehydrogenase but this enzyme does not show NAD-linked activity.
• 6.6. Kinetics of pyridoxal 5′-phosphate inhibition have indicated the presence of a lysine in the catalytic site for NADP⁺.

     

Sodium and potassium balance of captive meadow voles (Microtus pennsylvanicus) fed laboratory chow and vegetation diets

• 1.1. Mineral balance was studied in meadow voles (Microtus pennsylvanicus) maintained in the laboratory.
• 2.2. Urine and fecal Na⁺ contents of voles on low-Na⁺ diets were comparable to those reported for other herbivore species, but urine and fecal K levels were higher.
• 3.3. Voles approached Na⁺ balance (input = output) on diets with Na⁺ content as low as 56 ppm.
• 4.4. There was not a clearcut hypertrophy of the adrenal-gland zona glomerulosa in voles maintained on low-Na⁺ diets.
• 5.5. Plasma K content and bone water content were higher in voles maintained on high-Na ⁺ vegetation diets, suggesting expansion of extracellular fluid volume.

     

Na+-K+ ATPase and carbonic anhydrase activities in larvae,postlarvae and adults of the shrimp Penaeus japonicus (Decapoda,Penaeidea)

• 1.1. Activities of Na⁺-K⁺ ATPase and carbonic anhydrase were measured through the early post-embryonic development of Penaeusjaponicus. In adults, only the Na⁺-K⁺ ATPase activity was measured.
• 2.2. ATPase activity was variable in the successive development stages. From zero in nauplii, the activity slightly increased in zoeae, and rose sharply in mysis stages 2 and 3.
• 3.3. A further significant increase in activity was noted at the transition from late mysis to early postlarvae, concomitant with a change from the larval osmoconforming pattern of osmoregulation to the postlarval and adult hyper-hyporegulating pattern.
• 4.4. The activity of Na⁺-K⁺ ATPase, measured in isolated cephalothorax, increased from PL3 to PL4 to its maximum value in PL5; at this stage, osmoregulatory capacity was fully efficient.
• 5.5. In young stages of P. japonicus, the variations in Na⁺-K⁺ ATPase activity appear correlated with the development of osmoregulatory ultrastructures, and with osmoregulation and salinity tolerance.
• 6.6. These results are discussed with regard to their ecological and physiological implications.
• 7.7. In adults, the activity of Na⁺-K⁺ ATPase was high in gills and epipodites and no activity was detected in branchiostegites. These results are related to the ultrastructure of these organs.
• 8.8. The activity of carbonic anhydrase did not change significantly in larval and postlarval stages.
• 9.9. From these results, it is proposed that the effector sites of osmoregulation are located in branchiostegites, pleurae and epipodites in postlarvae, and in epipodites and mainly in gills in adults.

     

Mg2+-dependent (Na+ + K+)- and Na+-ATPases in the kidneys of the gilthead bream (Sparus auratus L.)

• 1.1. The (Na⁺ + K⁺)- and Na⁺-ATPases, both present in kidney microsomes of Sparus auratus L., have different activities and optimal assay conditions as, in the first of the two stocks of fish used (A), the spec. act. of the former is 51.7 μmol P_i mg prot⁻¹ hr⁻¹ at pH 7.5, 100 mM Na⁺, 10 mM K⁺, 17.5 mM Mg²⁺, 7.5 mM ATP and that of the latter is 6.5 μmol P_i mg prot⁻¹ hr⁻¹ at pH 6.5, 40 mM Na⁺, 4.0 mM Mg²⁺, 2.5 mM ATP.
• 2.2. Ouabain and vanadate specifically inhibit the (Na⁺ + K⁺)-ATPase but not the Na⁺-ATPase that is preferentially inhibited by ethacrynic acid.
• 3.3. While the (Na⁺ + K⁺)-ATPase is strictly specific for ATP and Na⁺, Na⁺-ATPase can be activated by various monovalent cations and, apart from ATP, hydrolyses CTP, though less efficiently.
• 4.4. The second stock B, subjected to higher salinity than A, shows an acidic shifted Na⁺-ATPase optimal pH, opposed to the stability of that of the (Na⁺ + K⁺)-ATPase, a decreased (Na⁺ + K⁺)-ATPase and a strikingly depressed Na⁺-ATPase.
• 5.5. The results are compared with literature data and discussed on the basis of the presumptive different roles as well as functional prevalence in various salinities of the two ATPases.