A note on eggshell porosity,nest humidity and the effects of DDE in the grey heron (Ardea cinerea)

• 1.1. Water vapour conductance (G_H2O) was determined for 25 grey heron Ardea cinerea eggs in the laboratory, and in nests during natural incubation at two Scottish colonies.
• 2.2. The mean G_H2O of eggs measured in the nest which successfully hatched was 9.0 mgH;O/mmHg/day and the mean water vapour pressure gradient between egg and nest (ΔP_H2O), measured using “calibrated” duck eggs, averaged at 31 mmHg (4.13 kPa).
• 3.3. Based on eggshell porosity results, from the eggs which hatched, such a gradient would result in a loss of water from the eggs during incubation equivalent to 11% of their fresh weight.
• 4.4. Shell thickness, the number of pores/cm² of eggshell and DDE content were also determined for the 25 eggs measured in the laboratory.
• 5.5. Eggs containing high levels of DDE had thinner shells, more pores in the eggshell and a higher overall eggshell porosity.
• 6.6. The main problem posed by a high level of DDE would appear, however, not to be an excessive water loss from the egg during incubation, but rather eggshell thinning leading to a loss of the egg due to breakage in the nest.

     

Effects of exercise-stress on ventilation,cardiac output and blood respiratory parameters in the carp,Cyprinus carpio

• 1.1. Carp (Cyprinus carpio) were stressed to exercise by rolling in a respiration chamber. Ventilatory water flow rate, cardiac output and blood respiratory parameters were determined.
• 2.2. During exercise, oxygen uptake increased about 3.5-fold and returned to pre-exercise level within 15 min.
• 3.3. This exercise-stress resulted in no plasma acidosis and in no swelling of the erythrocytes.
• 4.4. Ventilatory water flow rate increased 6-fold, whereas cardiac output increased 2-fold. Hence the ventilation-perfusion ratio increased during exercise.
• 5.5. During exercise, arterial O₂ content (CaO₂) increased due to increases in O₂ tension (PaO₂), O₂ saturation of hemoglobin (SaO₂) and hemoglobin concentration (Hb). On the other hand, Pv̄O₂ and Sv̄O₂ remained at the resting levels but Cv̄O₂ slightly increased due to an increase in Hb.
• 6.6. Arterial-venous O₂ difference (CaO₂-Cv̄O₂) increased by 38%, which was met by a much greater increase in CaO₂ than Cv̄O₂.

     

The effect of d2o on glycolysis by rat hepatocytes

• 1.1. The effect of incorporating D₂O into the incubation medium on glycolysis and gluconeogenesis by hepatocytes from fasted rats was examined.
• 2.2. The substitution by heavy water, D₂O, at concentrations from 10 to 40%, stimulated glucose uptake, lactate production and CO₂ yields from glucose. At 10 mM glucose, 40% D₂O doubled glucose uptake, increased CO₂ production by 40%, and increased lactate production by 350%.
• 3.3. The stimulation of lactate production decreased at higher glucose concentrations, but was still substantial even at 80 mM glucose.
• 4.4. There was no effect on CO₂ production above glucose concentrations of 30 mM.
• 5.5. Ten percent D₂O showed little inhibition of lactate uptake, its oxidation and gluconeogenesis. At 40% D₂O the inhibition ranged from 10 to 20%.
• 6.6. No effect of D₂O on the rate of glucokinase or glucose-6-phosphatase was observed.
• 7.7. The concentration of fructose, 2,6-P was not affected by D₂O

     

Effect of experimental ventilation of the skin on cutaneous oxygen uptake in the carp,Cyprinus carpio

• 1.1. Cutaneous O₂ uptake in the carp, Cyprinus carpio, was determined at various water flow rates across the skin (.V) ranging from 2.5 to 40 ml/min, using flow-through respirometers.
• 2.2. When thickness of water flow was 2mm, cutaneous O₂ uptake remained stable (about 3.8 nmol/cm²/min) at a .V of 20–40 ml/min and decreased with .V below 20 ml/min.
• 3.3. When thickness of water flow was 4 mm, cutaneous O₂ uptake decreased with .V below 40 ml/min.
• 4.4. Apparent water velocity (U') was calculated dividing .V by an area of a cross section of the water flow (0.5 and 1.0 cm² respectively). In both experiments, cutaneous O₂ uptake decreased with U' below 0.7 cm/sec.
• 5.5. This suggests that cutaneous O₂ uptake in the carp is limited at a low water velocity by a resistance of the hypoxic boundary layer.

     

Dissociation between several egg parameters in two quail strains genetically selected for resistance or sensitivity to acute hypoxia

• 1.1. Eggs laid by females of two strains of Japanese quail, selected in a divergent way towards survival to an acute normobaric hypoxic challenge, were compared for their mass, the mass and the thickness of their eggshell and their water conductance (g_h2o).
• 2.2. Adults and embryos of the Ls+ strain survive at 70%, whereas those of the Ls-strain survive only at 20% to the acute hypoxia.
• 3.3. While the birds of both sexes of each strain do not statistically differ either by their body masses or by various physiological and biochemical parameters, the eggs laid by the females of these strains differ significantly (0.001 < P < 0.01) in mass, eggshell thickness, egg shell mass and water vapor conductance (g_h2o).
• 4.4. Ls-quail lay lighter eggs with lighter and thinner eggshells and with higher g_h2o than Ls+ quail.
• 5.5. Crossing these two strains gives f₁ hybrids (Ls±) whose females lay eggs that are statistically (0.001 <P <0.05) different from those laid by Ls+ in egg masses and shell masses, and statistically (0.001 <P <0.05) different from those of Ls-in shell masses, shell thicknesses and g_h2o.

     

Factors affecting oxygen consumption in wild-caught yellow-bellied marmots (Marmota flaviventris)

• 1.1. All age groups gained mass during the active season, but mass-gain of adult females was delayed during lactation.
• 2.2. The relationship of body mass to metabolic rate varied widely; when the relationship was significant, R² varied from 10.3 to 72.6%. Body mass affects V_O2 more during lactation than at any other period.
• 3.3. Mean VinO₂ of adult males was higher in June than that of adult, non-lactating females.
• 4.4. V_O2 of reproductive females was significantly higher during lactation than during gestation or postlactation because specific V_O2 varied. Specific V_O2 of non-reproductive females declined over the active season.
• 5.5. Specific V_O2 of all age groups declined between the premolt and postmolt periods. The reduced maintenance costs can contribute 20–46% to daily growth.
• 6.6. Observed V_O2 was lower than the value predicted from intraspecific or interspecific Bm:M regressions.
• 7.7. V_O2 of wild-caught marmots was lower than that of marmots maintained in the laboratory, probably because of dietary differences.
• 8.8. Because basal metabolism is a stage on a food-deprivation curve, we suggest that basal metabolic rate is not an appropriate measure of the metabolic activity of free-ranging animals.

     

A comparative study of the respiratory properties and physiological function of haemocyanin in two burrowing and two non-burrowing crustaceans

• 1.1. Oxygen dissociation curves were constructed for the haemolymph of two non-burrowing, Galathea strigosa and Eupagurus bernhardus, and two burrowing crustaceans, C. cassivelaunus and Nephrops norvegicus. The p₅₀ at in vivo pH values and 10°C was 12.6 Torr in G. strigosa, 23 Torr in E. bernhardus, 3.1 Torr in C. cassivelaunus and 11.5 Torr in N. norvegicus.
• 2.2. The Bohr values (Δlogp₅₀/ΔpH) were high in all species ranging between −0.96 and −1.48. Cooperativity expressed as P₅₀ averaged 3.3, 3.8 and 3.8 in G. strigosa, E. bernhardus and N. norvegicus. respectively. A lower value of 2.2 was observed in C. cassivelaunus.
• 3.3. The oxygen affinity of the haemocyanin was relatively temperature independent, the values for ΔH at pH7.9 ranging between −5.1 and −18.1 kJmol⁻¹.
• 4.4. Haemolymph respiratory gas analysis showed values similar to those previously reported in crustaceans: p_aO₂ ranging between 44 and 107 Torr and p_vO₂ values between 18 and 24 Torr.
• 5.5. Pre-/post-branchial pH differences were small in G. strigosa, E. bernhardus and N. Norvegicus, but averaged 0.09 of a pH unit in C. cassivelaunus. p_aCO₂ and P_vCO₂ values ranged between 1.4 and 2.3 Torr.
• 6.6. In buried C. cassivelaunus both pre- and post-branchial oxygen tensions decreased, as did oxygen tension overall during respiratory pauses.
• 7.7. Cardiac output values were low, ranging between 59 and 71 ml kg⁻¹ min⁻¹ for all four species and calculated stroke volumes were realistic in terms of animal size.
• 8.8. In the non-burrowing species physically dissolved oxygen accounted for 5–21% of the oxygen transported to the tissues. In the burrowing species values of 40–77% were found.

     

In vitro substrate utilization for lipid synthesis in liver explants from hyperthyroid chickens

• 1.1. Indian River male broiler chickens growing from 7 to 28 days of age were fed diets containing 12, 18, 24 and 30% protein + 0 or 1 mg triiodothyronine (T₃)/kg of diet to study energetic costs of lipogenesis and the use of various substrates for in vitro lipogenesis.
• 2.2. De novo lipid and CO₂ production were determined in the presence of [1-¹⁴C]pyruvate, [2-¹⁴q]pyruvate, [3-¹⁴C]pyruvate, [2-¹⁴C]acetate and [U-¹⁴C]alanine.
• 3.3. Oxygen consumption was determined in mitochondrial preparations to estimate the energetic costs in expiants synthesizing lipid.
• 4.4. Radiolabeled CO₂ derived from [1-¹⁴C]pyruvate was used as an estimate of coenzyme A availability in liver expiants. Lipids derived from [2-¹⁴C]pyruvate, [2-¹⁴C]acetate and [U-¹⁴C]alanine estimate relative substrate efficiency.
• 5.5. Labeled CO₂ production from [1-¹⁴C]pyruvate was greatest in that group fed a 12% protein diet and least in the group fed a 30% protein diet.
• 6.6. In addition, T₃ increased CO₂ production from [1-¹⁴C]pyruvate.
• 7.7. The production of ¹⁴CO₂ from the second carbon of pyruvate or acetate was increased by T₃.
• 8.8. The low-protein diet (12% protein) increased (P <0.05) lipogenesis.
• 9.9. Adding T₃ to the diets decreased carbon flux into lipid from all substrates, but increased CO₂ production from all substrates without changing stage 3 and 4 respiration rates in mitochondrial preparations.
• 10.10. These observations imply that coenzyme A availability may have regulated de novo lipogenesis in the present study.
• 11.11. It was also concluded that previously noted effects of T₃ on intermediary metabolism may involve metabolic pathways that do not involve changes in mitochondrial function.

     

The effect of total environmental CO2 concentrations on the ion-permeability of shore crabs,Carcinus maenas (L.)

• 1.1. Salt exchange characteristics (permeability, half-time for salinity adaptation and net salt flux after a change in salinity) of adult shore crabs were studied in relation to experimentally increased external CO₂ (TCO₂ = carbon dioxide, carbonic acid, bicarbonate and carbonate) concentrations.
• 2.2. Up to about 15mM TCO₂/1, elevated external TCO₂ concentrations induce an increase in the salt permeability of shore crabs, resulting in higher passive salt fluxes across the body wall. The effect is most pronounced in larger animals (body weight > 25 g).
• 3.3. When external TCO₂ concentrations exceed internal TCO₂ concentrations, then permeability and salt exchange drop to low values, comparable to those observed in control animals. The results clarify a connection between blood gas transport and salt transport.
• 4.4. Elevated CO₂ levels are unfavourable by inhibiting the chloride/bicarbanate pump (thus disturbing the removal of metabolically produced CO₂ and the salt uptake in a hypotonic environment). High TCO₂ levels, up to about 20 mmol TCO₂/1, cause stress but Carcinus maenas can survive, at least temporarily, at the expense of metabolic energy.

     

Respiratory gas concentrations in the microhabitats of some florida arthropods

• 1.1. The concentrations (dry gas %) of oxygen and carbon dioxide were measured in a variety of microhabitats of arthropods in Florida: at the ends of the burrows of three spider species (Sphodros abboti, Geolycosa micanopy, Cyclocosmia torreya) and a tiger beetle (Megacephala carolina) larva, within ant (Solenopsis invicta) mounds, within stumps inhabited by termites (Reticulitermes flavipes), and within and under decaying hardwood logs.
• 2.2. Hypoxia and hypercarbia occurred in all microhabitats, with the ratio of oxygen decrement to carbon dioxide increment close to one. Changes for both gases were minor in the spider burrows, under decaying logs, and within ant mounds (<2.3% for O₂ and 1.1% for CO₂) and are probably physiologically unimportant to their inhabitants.
• 3.3. In contrast, %O₂ fell to as low as 12–14%, and CO₂ rose to as high as 6–8%, in the burrows of tiger beetle larvae, within decaying logs, and inside decaying stumps inhabited by termites.
• 4.4. Such changes, particularly for CO₂ may present a challenge to organisms living in these microenvironments.
• 5.5. Approximately 20–25% of the changes in the concentrations of respiratory gases in the burrows of tiger beetle larvae are attributable to the metabolism of the larva, the remainder being due to diffusional exchanges with the soil.

     

The influence of temperature on the haemocyanin function and oxygen uptake of the freshwater crab Potamonautes warreni calman

• 1.1. At 35°C a maximal VO₂ value of 110 ml O₂/kg/hr was obtained with a significant decrease in the value at 40°C.
• 2.2. The Bohr-effect for P. warreni is — 0.28 and does not change significantly at 15, 25 and 35°C.
• 3.3. The ability of the crab to extract oxygen from the water medium during a single exhalation is on average 41.2% whilst the limitation diffusion (L. diff, Piiper, [1982], A Companion to Animal Physiology, pp. 49–64. Cambridge University Press.) is 0.84.
• 4.4. Compared to land and marine crabs, in P. warreni, the P_aO₂ (29.5 mm Hg) and the P_vO₂ (15.3 mm Hg) is low.

     

Induction of locomotor behavior in the giant African snail,Achatina fulica

• 1.1. The locomotor-inducting factor of the giant African snail, Achatina fulica, was examined.
• 2.2. Snails showed nocturnal circadian behavior in relative humidity at least over 50%. Although the rhythmicity was independent of light and darkness, it was disturbed easily by hydration, and hydrated snails continued to locomote throughout the day. For induction of locomotor behavior, relative humidity over 50% was the fundamental factor and water is shown to be the limiting factor for the endogeneous circadian oscillator.
• 3.3. The integument of snails showed a higher water permeability. Through the integument, hemolymph osmolality changed easily according to hydration and dehydration from about 120 to 400 mOsm/kg H₂O. Circadian behavior was induced in snails in which hemolymph osmolality ranged from about 130 to 230 mOsm/kg H₂O.
• 4.4. By hydration, hemolymph osmolality in quiescent and estivated snails which have higher osmolality decreased gradually and then they began to locomote according to the degree of dilution, and vice versa. The induction of behavior in these snails was controlled by low hemolymph osmolality.
• 5.5. Together with the endogeneous rhythmicity, water environment was shown to be the key factor for the induction of locomotor behavior.
• 6.6. Based on these results, the mechanisms of the induction of locomotor behavior in terrestrial pulmonates are proposed.

     

Evidence for a non-respiratory intralamellar shunt in perfused rainbow trout gills

• 1.1. Rainbow trout (Salmo gairdneri Rich.) heads were perfused with phosphate buffered saline containing 10 μM adrenaline. The gills were ventilated with aerated water (PI_O2 = 20.7–20.9 kPa). Pv_O2 and Pa_O2 were measured and PI_O2 controlled.
• 2.2. An equilibrium between PI_O2 and Pa_O2 when Pv_O2 = 0 kPa, was never observed. The reasons for this difference in O₂ tensions were evaluated.
• 3.3. Perfusion with nitrogen equilibrated saline (Pv_O2 = 0 kPa) resulted in Pa_O2 of 16.4 ± 0.4 kPa. After a change to aerated saline (Pv_O2 20.7–20.9 kPa) Pa_O2 increased to 17.6 ± 0.5 kPa. In this situation when Pv_O2 = PI_O2 the PI_O2 − Pao, difference showed that gill tissue consumed O₂ from the saline.
• 4.4. As expected, an inhibition of this O₂ consumption with cyanide in the ventilation water increased Pa_O2 to 20.1 ± 0.3 kPa. However a return to the N₂-equilibrated saline (Pv_O2 = 0 kPa), still in presence of cyanide, decreased Pa_O2 to 17.2 ± 0.5 kPa. This indicates that O₂ consumption of gill tissue is not the only factor limiting O₂- transfer.
• 5.5. An increase of perfusion flow (Q) within a physiological flow rate from 0.5 to 3.0 ml min⁻¹ (100 g fish)⁻¹ did not significantly affect Pa_O2 Thus, the O₂ transfer in the perfused gills appear to be rather limited by perfusion than by diffusion.
• 6.6. Ventilation at the rate used (800–1000 ml min⁻¹ (100 g fish)⁻¹)did not limit O₂-transfer. The PI_O2–Pa_O2 difference was not caused by a “water shunt”.
• 7.7. We suggest therefore, that the PI_O2-Pa_O2 difference in saline perfused gills is a result of a shunt, i.e. perfusate flow by-passing the gas exchange area in the gill circulation. The shunt was calculated to 11–22 of the total perfusion flow (Q).

     

Standard and pH-affected hemoglobin-O2 binding curves of Sprague-Dawley rats under normal and shifted P50 conditions

• 1.1. The oxygen saturation (SO₂) was determined of Sprague-Dawley rat blood having increased hemoglobin (Hb)-O₂ affinity (P₅₀ < 37mmHg) or capacity (C_max) over a range of pH's.
• 2.2. Rats were untreated (K), or had passed 14 d drinking 0.5% saline (C; ctrl) or NaOCN (N; chronically low P₅₀ high C_max), 5000m altitude acclimatization (H; high C_max), or exchange transfusion with OCN⁻-Hb red cell blood (X; acutely low P₅₀).
• 3.3. The P₅₀ [mmHg], Hill's “n”, and C_max [ml O₂/100 ml], measured after tonometry, were 36.0, 2.60 and 20.6 (K), 32.6, 2.50 and 21.8 (C), 18.3, 2.35 and 23.9 (N), 36.0, 2.60 and 29.4 (H), and 24.9, 2.73 and 22.3 (X).
• 4.4. Oxygen dissociation curves (ODC's), derived from simultaneous SO₂ and PO₂ measurements during deoxygenation (PO₂: 100-0 mmHg) of blood (normal and acidified with CO₂ or lactic acid), delivered Bohr coefficients (BC_CO2, BC_Lac) each differing between groups (C vs N) above SO₂ 50%; within groups BC_CO2 vs BC_Lac differed at SO₂ 10–90% (P < 0.05).
• 5.5. Group-specific ODC's and pH-shifted curves (± 0.05, ± 0.10 and ±0.15 units from 7.4, relying on BC_CO2) are plotted for direct reading of SO₂ and, with C_max, accurate data on blood O₂ content are obtained; corrections for lactic acidosis are discussed.

     

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.

     

The effect of temperature on the acid-base status of the blood of the hatching quail (Coturnix c. japonica)

• 1.1. The ambient temperature of embryos of pipped eggs was reduced from 38 to 28°C for a period of 45 min.
• 2.2. The blood P_CO2 was lower and the blood more alkaline at 28°C than at 38°C.
• 3.3. At 28°C plasma [HCO₃⁻] ] was lower than predicted from the blood buffer line determined in vitro.
• 4.4. The plasma concentrations of strong ions and lactate were the same at both temperatures.
• 5.5. After the ambient temperature had been returned to 38°C for a period of 45 min, blood pH was more acidic than before cooling, but there was no difference in blood P_CO2.
• 6.6. The plasma [HCO₃⁻] was the same as that at 28°C and plasma [K⁺] was higher than before cooling.
• 7.7. The results arc discussed in relation to the factors affecting blood pH in embryos at this stage of development.

     

Comparative study of the oxyhaemoglobin dissociation curve of four mammals: Man,dog, horse and cattle

• 1.1. The entire oxygen dissociation curve (ODC) and the effects of temperature, pH and 2,3-diphosphoglycerate (DPG) on this curve, have been compared in four mammalians: man, dog, horse and cattle.
• 2.2. If the oxyphoric capacities are similar between these species (around 1.39ml O₂/gHb), their P50, measured in standard conditions, i.e. at pH 7.4;.pCO₂ 40mmHg and T 37°C, varies between 23.8 (± 0.8) mmHg for the horse, 25.0 (± 1.4) mmHg for cattle, 26.6 (± 1.2) for man and 28.8 (± 2.6) mmHg for the dog.
• 3.3. The higher dispersion of the dog's P50 is due to difference between breeds; in seven breeds investigated, the P50 ranges from 25.8 (spaniel) to 35.8 (hound).
• 4.4. We noted no sex difference in the four species.
• 5.5. The DPG level is confirmed to be low in cattle (< 1 μmol/gHb) as compared to man (13.5 ± 2.1 gmmol/gHb), horse (16.9 ± 1.1 gmmol/gHb) and dog (19.4 ± 2.8 μmol/gHb).
• 6.6. The oxygen exchange fraction defined as the difference in vol% between a pO₂ of 80 and 35 mmHg is, respectively, 3.6 (± 0.6) vol% for cattle, 4.0 (0.4) vol% for the horse, 5.5 (± 0.5) vol% for man and 6.6 (± 1.7) vol% for the dog.
• 7.7. The position and shape of the ODC, as well as T, DPG and pH effects, indicate that the haemoglobin of man and dog seem better adapted to O₂ delivery as compared to the horse and cattle.

     

Sea water drinking as a homeostatic response to dehydration in hatchling loggerhead turtles Caretta caretta

• 1.1. Hatching Caretta caretta may lose up to 12% of their initial hatched weight from water loss during emergence from the nest.
• 2.2. After subsequent osmotic and excretory water loss in sea water, hatchlings will drink sea water (166 μl 100 g⁻¹ hr⁻¹) and return to their initial weight within 10–15 days, without feeding.
• 3.3. There were no significant changes in plasma osmolarity or sodium levels over this period.
• 4.4. This osmoregulatory strategy is in marked contrast to that seen in the estuarine crocodile, Crocodylus porosus.

     

O2-binding by the blood of the landhopper,Arcitalitrus dorrieni (Hunt) (Crustacea: Amphipoda)

• 1.1. The O₂-binding characteristics of the blood of the euterrestrial amphipod (landhopper) Arcitalitrus dorrieni have been studied.
• 2.2. The blood exhibited a low O₂ affinity, with a p₅₀ (at pH = 7.8) of 21.4 torr (10°C). Affinity decreased with an increase in temperature at constant pH (ΔH = − 79.4kJ/mol) but the Bohr factor (ΔlogP₅₀/Δ pH = −0.67) was unaffected.
• 3.3. The O₂-carrying capacity of the blood was moderate (1.51 ml/100 ml)
• 4.4. The results support the hypothesis that the blood of terrestrial amphipods is characterized by having a low affinity pigment.

     

Intestinal l-methionine transport in the cultured gilthead bream (Sparus aurata)

• 1.1. The influx and transepithelial movements of l-methionine and its effects on the electrophysiology and Na-Cl-transport in upper and lower intestine of the cultured fish, Spanis aurata, were measured.
• 2.2. The K_m and V_max of l-methionine influx into the tissues were higher in lower intestine than in upper intestine. A prominent diffusion-like transport component was also measured in both segments during influx experiments.
• 3.3. Net transepithelial fluxes of l-methionine (1 mM) were observed in both upper and lower intestine, this transport being Na⁺-dependent.
• 4.4. The two intestinal segments exhibited an electrical potential difference (PD) and a short circuit current (I_sc) serosa negative or near zero. Tissue conductance (G_t) was higher in posterior than in lower intestine.
• 5.5. Addition of l-methionine to the mucosal side of lower or upper intestine did not induce changes in PD in either part.
• 6.6. Isotopic fluxes of Cl⁻ or Na⁺ measurements under short circuit conditions showed that there were no net Cl⁻ or Na⁺ transport in either part.
• 7.7. l-Methionine additions to the mucosa did not induce changes in unidirectional fluxes of Cl⁻ or Na⁺ or in the (I_sc) in either the anterior or posterior intestine.