Oxygen transfer properties and dimensions of red blood cells in high-altitude camelids,dromedary camel and goat

Summary To estimate the advantage of the small red blood cells (RBC) of high-altitude camelids for O₂ transfer, the kinetics of O₂ uptake into and release from the RBC obtained from llama, vicuña and alpaca were investigated at 37°C with a stopped-flow technique. O₂ transfer conductance of RBC (G) was estimated from the rate of O₂ saturation change and the corresponding O₂ pressure difference between medium and hemoglobin. For comparison, O₂ kinetics for the RBC of a lowaltitude camelid (dromedary camel) and the pygmy goat were determined and previously measured values for human RBC were used. O₂ transfer of RBC was found to be strongly influenced by extracellular diffusion, except with O₂ release into dithionite solutions of sufficiently high concentration (>30 mM). TheG values measured in these standard conditions,G _st (in mmol · min^–1 · Torr^–1 · (ml RBC)^–1) were: high-altitude camelids, 0.58 (averaged for llama, alpaca and vicuña since there were no significant interspecific differences); camel 0.42; goat, 0.42; man, 0.39. The differences can in part be attributed to expected effects of the size and shape of the RBC (volume, surface area, mean thickness), as well as to the intracellular O₂ diffusivity which depends on the concentration of cellular hemoglobin. The highG _st of RBC of highaltitude camelids may be considered to enhance O₂ transfer in lungs and tissues. But the O₂ transfer conductance of blood, , equal toG _st multiplied by hematocrit (in mmol · min^–1 · Torr^–1 · (ml blood)^–1), was only slightly higher as compared to other species: 0.20 (llama, alpaca, vicuña), 0.14 (camel), 0.18 (goat), 0.17 (man).Abbreviations DPG 2,3-diphosphoglycerate - G conductance - Hb hemoglobin - RBC red blood cells - percent saturation of hemoglobin     

Interaction of allosteric effectors with alpha-globin chains and high altitude respiration of mammals. The primary structure of two tylopoda hemoglobins with high oxygen affinity: vicuna (Lama vicugna) and alpaca (Lama pacos)

Polyacrylamide gel electrophoresis and ion-exchange chromatography revealed one hemoglobin component for vicuna (Lama vicugna) and alpaca (Lama pacos). Following chain separation by chromatography on carboxymethyl-cellulose, the amino-acid sequences were elucidated for the alpha- and beta-chains of both hemoglobins using automatic Edman degradation of the chains and the tryptic peptides. Vicuna and alpaca have identical beta-chains showing no substitutions to llama (Lama glama) either. In the alpha-chains alpaca differs from llama by the exchange of one amino-acid residue: alpha 122(H5)Asp----His. The same substitution is present in vicuna too, but in addition we found two more exchanges: alpha 10(A8)Ile----Val and alpha 130(H13)Ala----Thr. The close relationship between llama and alpaca suggests that they both originate from the wild guanaco, and there is no domesticated form of vicuna. The sequence data show that the higher oxygen affinity in vicuna compared to llama and alpaca must be due to the alpha-chains as the beta-chains are identical. The significance of the substitutions in alpha 122(H5), an alpha 1/beta 1-contact, and alpha 130(H13) is discussed.     

Maximum Running Speed of Captive Bar-Headed Geese Is Unaffected by Severe Hypoxia

While bar-headed geese are renowned for migration at high altitude over the Himalayas, previous work on captive birds suggested that these geese are unable to maintain rates of oxygen consumption while running in severely hypoxic conditions. To investigate this paradox, we re-examined the running performance and heart rates of bar-headed geese and barnacle geese (a low altitude species) during exercise in hypoxia. Bar-headed geese (n = 7) were able to run at maximum speeds (determined in normoxia) for 15 minutes in severe hypoxia (7% O₂; simulating the hypoxia at 8500 m) with mean heart rates of 466±8 beats min⁻¹. Barnacle geese (n = 10), on the other hand, were unable to complete similar trials in severe hypoxia and their mean heart rate (316 beats.min⁻¹) was significantly lower than bar-headed geese. In bar-headed geese, partial pressures of oxygen and carbon dioxide in both arterial and mixed venous blood were significantly lower during hypoxia than normoxia, both at rest and while running. However, measurements of blood lactate in bar-headed geese suggested that anaerobic metabolism was not a major energy source during running in hypoxia. We combined these data with values taken from the literature to estimate (i) oxygen supply, using the Fick equation and (ii) oxygen demand using aerodynamic theory for bar-headed geese flying aerobically, and under their own power, at altitude. This analysis predicts that the maximum altitude at which geese can transport enough oxygen to fly without environmental assistance ranges from 6,800 m to 8,900 m altitude, depending on the parameters used in the model but that such flights should be rare.     

DNA composition in South American camelids I. Characterization and in situ hybridization of satellite DNA fractions

The DNA composition and the in situ hybridization of satellite fractions were analysed in the New World camelids llama, alpaca, guanaco and vicuña. In the four camelid forms, it was possible to identify a similar main band DNA and five satellite fractions (I–V) with G+C base contents ranging from 32% to 66%. Satellites II–V from llama were in situ reannealed on chromosomes from the four camelid forms. The results obtained were: (a) the four satellites hybridized with regions of C-banding (centromeric regions of all chromosomes and short arms of some autosomes); (b) in general, homologous hybridizations (llama DNA versus llama chromosomes) were more efficient than heterologous reassociations; there were however three exceptions to this rule (vicuña and alpaca satellite fraction II, chromosome group B; vicuña fraction V, chromosome groups A and B); (c) X chromosomes from the four camelids had satellites III–V but lacked satellite II, (d) no satellite fraction was detected on chromosome Y. The analysis of the in situ hybridization patterns allowed to conclude that most or all C-banded chromosome regions comprise several satellite DNA fractions. It is, moreover, proposed that there is an ample interspecies variation in the number of chromosomes that cross-react with a given satellite fraction. Our data give further support to the close genomic kinship of New World camelids.     

Cardiovascular and respiratory physiology of tuna: adaptations for support of exceptionally high metabolic rates

Synopsis Both physical and physiological modifications to the oxygen transport system promote high metabolic performance of tuna. The large surface area of the gills and thin blood-water barrier means that O₂ utilization is high (30–50%) even when ram ventilation approaches 101 min^–1kg^–1. The heart is extremely large and generates peak blood pressures in the range of 70–100 mmHg at frequencies of 1–5 Hz. The blood O₂ capacity approaches 16 ml dl^–1 and a large Bohr coefficient (–0.83 to –1.17) ensures adequate loading and unloading of O₂ from the well buffered blood (20.9 slykes). Tuna muscles have aerobic oxidation rates that are 3–5 times higher than in other teleosts and extremely high glycolytic capacity (150 mol g^–1 lactate generated) due to enhanced concentration of glycolytic enzymes. Gill resistance in tuna is high and may be more than 50% of total peripheral resistance so that dorsal aortic pressure is similar to that in other active fishes such as salmon or trout. An O₂ delivery/demand model predicts the maximum sustained swimming speed of small yellowfin and skipjack tuna is 5.6 BL s^–1 and 3.5 BL sec^–1, respectively. The surplus O₂ delivery capacity at lower swimming speeds allows tuna to repay large oxygen debts while swimming at 2–2.5 BL s^–1. Maximum oxygen consumption (7–9 × above the standard metabolic rate) at maximum exercise is provided by approximately 2 × increases in each of heart rate, stroke volume, and arterial-venous O₂ content difference.Paper from International Union of Biological Societies symposium The biology of tunas and billfishes: an examination of life on the knife edge, organized by Richard W. Brill and Kim N. Holland.     

Mitochondrial DNA structure and organization of the control region of South American camelids

This work presents the mitochondrial DNA molecular organization of the control region (CR) of South American camelids. Sequencing of five individuals each of guanaco, llama, alpaca and vicuna species showed that this region spans 1060 bp including three conserved sequence blocks (CSB I–III) adjacent to the tRNAPhe gene, a conserved central domain and one extended termination‐associated sequence in the 3′ domain of the CR close to the tRNAPro gene. A repeated array formed by three units of 26 bp was detected between CSB I and II. Alignment of the CR sequences from the four species shows a 337‐bp segment that includes most of the nucleotide variability with 10 polymorphic sites. We suggest the use of this segment as a molecular marker to infer data on camelid genetic relationships and population diversity studies.     

Increases in arterial blood oxygen during exercise in the lemon shark (Negaprion brevirostris)

Summary Polyethylene cannulae were implanted in pre- and post-branchial blood vessels allowing nonstressful blood sampling over a variety of activity ranges in an active tropical elasmobranch, the lemon shark (Negaprion brevirostris). TheP ₅₀ was found to be 11.8 Torr at 24°C and pH of 7.7. A Bohr shift of –0.36 was also found. BloodP _{o 2} and oxygen content were measured during rest, routine swimming, and exercise in unanesthetized, free swimming juveniles. Under all conditions venous oxygen levels were low with venousP _{o 2} of 7.1±2.7 Torr, and venous oxygen content ( ) of 0.56±0.4 vol%. However, a large variability was found in arterial blood measurements. ArterialP _{o 2} ranged from 7 to 80 Torr, while arterial oxygen content (Ca_{o 2}) varied from 1.6 vol% to 6.8 vol% among ten experimental animals. A significant increase in arterialP _{o 2}, oxygen content, and hematocrit was noted during increased activity. Since the venous system provides little or no oxygen reserve, increased oxygen extraction from the blood ( ) appears to be met by an increase inCa_{o 2} rather than a decrease in . Mechanisms to accomplish this may include increasing hematocrit and vacular gill shunts.     

Ventilation and gas exchange in the diamondback water snake,Natrix rhombifera

Summary Simultaneous measurements of pulmonary and cutaneous oxygen and carbon dioxide exchange, pulmonary ventilation and heart rate were made on the diamondback water snake,Natrix rhombifera at 28°C using body plethysmography. Resting lung volume, maximum lung volume and tracheal volume were also measured.The following mean values were measured in undisturbed snakes breathing room air: total (pulmonary and cutaneous) O₂ uptake 46 mol · (kg min)^–1; total CO₂ output, 49 mol · (kg min)^–1; tidal volume, 12 ml (BTPS) · kg^–1; ventilatory rate, 6.9 min^–1; heart rate, 42 min^–1. From the measurements of tracheal volume, the effective (alveolar) ventilation was estimated as approximately 70% of total ventilation resulting in effective pulmonary and of 130 Torr and 20 Torr respectively. Cutaneous exchange accounted for 8.1% of the total and 12.4% of the total .Resting lung volume of anaesthetized snakes was 75 ml (BTPS) · kg^–1, maximum lung volume was 341 ml (BTPS) · kg^–1 and tracheal volume was 3.9 ml (BTPS) · kg^–1.     

Oxygen transport and cardiovascular responses in skipjack tuna (Katsuwonus pelamis) and yellowfin tuna (Thunnus albacares) exposed to acute hypoxia

Summary Responses to acute hypoxia were measured in skipjack tuna (Katsuwonus pelamis) and yellowfin tuna (Thunnus albacares) (1–3 kg body weight). Fish were prevented from making swimming movements by a spinal injection of lidocaine and were placed in front of a seawater delivery pipe to provide ram ventilation of the gills. Fish could set their own ventilation volumes by adjusting mouth gape. Heart rate, dorsal and ventral aortic blood pressures, and cardiac output were continuously monitored during normoxia (inhalant water (PO ₂>150 mmHg) and three levels of hypoxia (inhalant water PO ₂130, 90, and 50 mmHg). Water and blood samples were taken for oxygen measurements in fluids afferent and efferent to the gills. From these data, various measures of the effectiveness of oxygen transfer, and branchial and systemic vascular resistance were calculated. Despite high ventilation volumes (4–71·min^-1·kg^-1), tunas extract approximately 50% of the oxygen from the inhalant water, in part because high cardiac outputs (115–132 ml·min^-1·kg^-1) result in ventilation/perfusion conductance ratios (0.75–1.1) close to the theoretically ideal value of 1.0. Therefore, tunas have oxygen transfer factors (ml O₂·min^-1·mmHg^-1·kg^-1) that are 10–50 times greater than those of other fishes. The efficiency of oxygen transfer from water in tunas (65%) matches that measured in teleosts with ventilation volumes and order of magnitude lower. The high oxygen transfer factors of tunas are made possible, in part, by a large gill surface area; however, this appears to carry a considerable osmoregulatory cost as the metabolic rate of gills may account for up 70% of the total metabolism in spinally blocked (i.e., non-swimming) fish. During hypoxia, skipjack and yellowfin tunas show a decrease in heart rate and increase in ventilation volume, as do other teleosts. However, in tunas hypoxic bradycardia is not accompanied by equivalent increases, in stroke volume, and cardiac output falls as HR decreases. In both tuna species, oxygen consumption eventually must be maintained by drawing on substantial venous oxygen reserves. This occurs at a higher inhalant water PO₂ (between 130 and 90 mmHg) in skipjack tuna than in yellowfin tuna (between 90 and 50 mmHg). The need to draw on venous oxygen reserves would make it difficult to meet the oxygen demand of increasing swimming speed, which is a common response to hypoxia in both species. Because yellowfin tuna can maintain oxygen consumption at a seawater oxygen tension of 90 mmHg without drawing on venous oxygen reserves, they could probably survive for extended periods at this level of hypoxia.Abbreviations BP_da, BP_va dorsal, ventral aortic blood pressure - C _aO₂, C _vO₂ oxygen content of arterial, venous blood - DO₂ diffusion capacity - E_b, E_w effectiveness of O₂ uptake by blood, and from water, respectively - Hct hematocrit - HR heart rate - PCO₂ carbon dioxide tension - P _aCO₂, P _vCO₂ carbon dioxide tension of arterial and venous blood, respectively - PO₂ oxygen tension - P _aO₂, P _vO₂, P _iO₂, P _cO₂ oxygen tension of arterial blood, venous blood, and inspired and expired water, respectively - pHa, pHv pH of arterial and venous blood, respectively - P_w—b effective water to blood oxygen partial pressure difference - Pg partial pressure (tension) gradient - cardiac output - R vascular resistance - SV stroke volume - SEM standard error of mean - TO₂ transfer factor - U utilization - _g ventilation volume - O₂ oxygen consumption     

Relationship of extracellular dopamine in striatum of newborn piglets to cortical oxygen pressure

The present studies describes the relationship between extracellular dopamine in striatum of newborn piglets and cortical oxygen pressure. The extracellular level of dopamine was measured by in vivo microdialysis and the oxygen pressure in the cortex was measured by phosphorescence lifetime of oxygen probe in the blood. Controlled, graded levels of hypoxic insult to the brain of animals were generated by decreasing of the oxygen fraction in the inspired gas (FiO₂) from 21% to 14%, 11%, and 9%. This resulted in decrease in the cortical oxygen pressure from 31–35 Torr to about 24 Torr, 15 Torr and 4 Torr, respectively. The changes in extracellular level of dopamine, DOPAC and HVA were dependent on changes in cortical oxygen pressure. Stepwise decrease in the cortical oxygen pressure (see above) caused increases in extracellular dopamine of about 80%, 200% and 550%, respectively. The levels of DOPAC and HVA progressively decreased and when cortical oxygen decreased to 4–6 Torr were about 50% and 70% of control. respectively. After return of FiO₂ to control (21%), the cortical oxygen pressure rapidly increased to above normal, then returned to control values. The extracellular levels of dopamine, DOPAC, and HVA recovered more slowly, attaining control values in about 30 minutes. The data show that extracellular levels of dopamine increase with even very small decreases in oxygen pressure. Thus, there is no oxygen reserve which protects dopamine release and metabolism from decrease in oxygen pressure.     

Rotifer distribution in relation to temperature and oxygen content

Lunzer Obersee, a small lake located at an altitude of 1100 m above sea level, was investigated from July 1985 to October 1987. The rotifer community consists of 7 dominant species, 7 subdominant species and 34 species which occasionally occurred in the plankton. The dominant species show rather different demands in relation to temperature and oxygen content; e.g.: Filinia hofmanni was found at a wide range of oxygen concentrations (0.6–13.3 mg O₂l^–1) and low temperatures (4–6 °O, living in the upper water layers (1–7 m) during spring and in the deeper, anoxic zone in summer. In contrast, Asplanchna priodonta was found at rather high oxygen contents (> 9 mg O₂ l^–1), ), and showed a wide range of temperature tolerance (4–15 °C).On the basis of field data the temperature and oxygen requirements of several species are described and discussed.     

Fluctuation analysis of short-circuit current in a warm-blooded sodium-retaining epithelium: Site current,density, and interaction with triamterene

Summary Density and conductance of the Na-site in hen coprodeum were studied by employing fluctuation analysis of shortcircuit current at sodium concentrations from 26 to 130mm. Fluctuations of current in the frequency range 2–800 Hz were induced by triamterene, a reversible blocker of conducting epithelial Na-sites. At 130mm Na the site density was 5.8±1.0 m^–2 and the site conductance was 4 pS. This conductance is equal to that of the frog skin (W. Van Driessche and B. Lindemann, 1979,Nature (London) 282:519–520). Extrapolation of site density to zero sodium renders a total of 38±28 sites m^–2, which is compared with other estimates for the coprodeum. The site-triamterene association and dissociation constants were 9.5±0.4 rad sec^–1 m ^–1 and 255±20 rad sec^–1 and they were independent of external sodium concentration. An analysis of the affinity constant for triamterene based on the DC-short-circuit current was found to be unrelated to the external sodium concentration and identical to that obtained from fluctuation analysis indicating a noncompetitive interaction between sodium and triamterene. Due to the oxygen demand of the epithelium we have developed an experimental method using short data processing times. A new analytical approach using integration of the power density spectrum proved necessary because of low signal-to-noise ratios.     

Respiratory,cardiovascular and metabolic adjustments during steady state swimming in the green turtle,Chelonia mydas

Summary Heart rate and pulmonary artery blood flow of resting green turtles,Chelonia mydas, at 29°C increased with lung ventilation (heart rate from 24±5 to 51±8 beats min). When swimming at 0.6 m s^–1 in water at 30°C, oxygen uptake was 2.83 times and respiratory frequency was 2.75 times the resting values. Heart rate was 1.33 times that during ventilation at rest but 2.83 times that at the end of a breath hold at rest. Partial pressures of oxygen and carbon dioxide, lactic acid concentration and pH of arterial blood, when swimming at 0.5 m s^–1, were similar to those soon after ventilation at rest. Pulmonary blood flow did not decline to low levels between breaths, when the animals were swimming, as it did when they were at rest.In active turtles it appears that pulmonary perfusion remains elevated, supplying oxygen to the locomotory muscles at a sufficiently high rate to support the complete aerobic production of energy, and that respiratory frequency is kept as low as possible, as surfacing for air increases the metabolic cost of swimming.     

Respiratory adaptations to diving in the nile monitor lizard,Varanus niloticus

Summary The objectives of this study included directin vivo measurements of circulating blood gases, pH, heart rate, and blood pressure during voluntary dives of unrestrained Nile monitor lizards. A Radiometer flow-through cuvette was employed for continuous recording of arterial PO₂, PCO₂ and pH. Hematological properties revealed no particular adaptations for diving. Mean values were: hematocrit = 24%; hemoglobin concentration = 7.1 g %; oxygen capacity = 9.3 vol %; red cell dimensions = 22×12 ; red cell count = 0.67 million/l. The respiratory properties of the blood, studiedin vitro andin vivo, show distinct adaptations to habitual diving. Oxygen affinity of blood is low (P₅₀ = 42.4 mm Hg at pH 7.45, 25 °) and the dissociation curve is markedly sigmoid (n = 3.1). These features, coupled with a Bohr factor ( logP ₅₀/pH) of –0.48, ensure increased utilization of oxygen while maintaining relatively high tissue PO₂. Arterial pH decreases during diving from about 7.5 to 7.1 due to combined respiratory and metabolic acidosis. High plasma bicarbonate (30 mM/l at PCO₂ = 25 mm Hg) and a buffering capacity of H C₃ ^–O/ pH = 18.9 mM/l increase the tolerance to this acidosis and prolong diving time. Thein vivo oxygen dissociation curve shows a 90 % depletion of arterial oxygen content during typical dives. Diving elicited a rapidly developing bradycardia with maximum of 85 % reduction in heart rate. The temperature sensitivity of HbO₂ binding was very low (H = –3kcal). This would minimize the HbO₂ affinity increase accompanying the decrease in body temperature likely to occur in lizards going from sun basking to submergence in water.Supported by a grant from the Danish Natural Science Research Council.     

Heart and circulatory functions in a spider (Eurypelma californicum): the effects of hydraulic force generation

Summary In the tarantulaEurypelma californicum, the relationships between heart activity, circulation and the generation of hydraulic pressure for locomotion were studied. Several new techniques were employed.Mean resting heart rate was 21 beats min^–1 rising to 90 beats min^–1 after burst activity. Decay time to resting rates was related to the increase of heart rate. Post-recovery resting rates were usually elevated in comparison with rates after very long resting periods.A relative measure of heart amplitude was obtained. Four distinct patterns could be distinguished: (i) regular beats; (ii) short-term fluctuations of amplitude within a few heart beats; (iii) a slow rhythmic change of heart/pericardium filling, and (iv) non-periodic, stronger amplitude changes during periods of activity.During locomotion, heart rate rises with maximum rates often reached only minutes after the onset of activity. The rising phase is often characterized by irregularities and a reduction of heart amplitude.Prosomal hemolymph pressure in resting, restrained animals was 41±19 Torr, rising to ca. 90, and 217±48 Torr during walking and fast sprints, respectively. Values in unrestrained spiders were similar. Opisthosomal hemolymph pressures were ca. 20 Torr in resting animals, rising to 40–60 Torr during locomotion.Opisthosomal volume changes were measured. A small volume of hemolymph moved from the prosoma to the opisthosoma at the onset of locomotion, but following activity this volume quickly returned to the prosoma.The simultaneous measurement of carapace depression, opisthosomal volume changes and hemolymph pressures, and heart activity revealed the relationship between circulation and hydraulic force generation. The direction of hemolymph flow was also studied. In non-active animals, the heart occasionally changes its main pumping direction. During locomotion, hemolymph flow from the heart to the prosoma is often reduced or stopped. With a slight delay, hemolymph flow to the opisthosoma is increased. The critical pressure at which prosomal perfusion from the heart is halted is 50–70 Torr.It is concluded that anterior and posterior circulations are separate: hemolymph returning from the prosoma passes only through the anterior lungs, while hemolymph returning from the opisthosoma passes through the posterior lungs.Dedicated to Dr. Rosemarie John, in recognition of her unflagging enthusiasm and support for zoological researchProf. B. Linzen unexpectedly died on August 5, 1988     

Electrical properties of chloride transport across theNecturus proximal tubule

Summary The chloride conductance of the basolateral cell membrane of theNecturus proximal tubule was studied using conventional and chloride-sensitive liquid ion exchange microelectrodes. Individual apical and basolateral cell membrane and shunt resistances, transepithelial and basolateral, cell membrane potential differences, and electromotive forces were determined in control and after reductions in extracellular Cl^–. When extracellular Cl^– activity is reduced in both apical and basolateral solutions the resistance of the shunt increases about 2.8 times over control without any significant change in cell membrane resistances. This suggests a high Cl^– conductance of the paracellular shunt but a low Cl^– conductance of the cell membranes. Reduction of Cl^– in both bathing solutions or only on the basolateral side hyperpolarizes both the basolateral cell membrane potential difference and electromotive force. Hyperpolarization of the basolateral cell membrane potential difference after low Cl^– perfusion was abolished by exposure to HCO ₃ ^– -free solutions and SITS treatment. In control conditions, intracellular Cl^– activity was significantly higher than predicted from the equilibrium distribution across both the apical and basolateral cell membranes. Reducing Cl^– in only the basolateral solution caused a decrease in intracellular Cl^–. From an estimate of the net Cl^– flux across the basolateral cell membrane and the electrochemical driving force, a Cl^– conductance of the basolateral cell membrane was predicted and compared to measured values. It was concluded that the Cl^– conductance of the basolateral cell membrane was not large enough to account for the measured flux of Cl^– by electrodiffusion alone. Therefore these results suggest the presence of an electroneutral mechanism for Cl^– transport across the basolateral cell membrane of theNecturus proximal tubule cell.     

Photosynthetic and leaf morphological characteristics in Leucaena leucocephala as affected by growth under different neutral shade levels

Morphological and physiological measurements on individual leaves of Leucaena leucocephala seedlings were used to study acclimation to neutral shading. The light-saturated photosynthetic rate (P_{n max}) ranged from 19.6 to 6.5 mol CO₂ m^–2 s^–1 as photosynthetic photon flux density (PPFD) during growth decreased from 27 to 1.6 mol m^–2 s^–1. Stomatal density varied from 144 mm^–2 in plants grown in high PPFD to 84 mm^–2 in plants grown in low PPFD. Average maximal stomatal conductance for H₂O was 1.1 in plants grown in high PPFD and 0.3 for plants grown in low PPFD. Plants grown in low PPFD had a greater total chlorophyll content than plants grown in high PPFD (7.2 vs 2.9 mg g^–1 on a unit fresh weight basis, and 4.3 vs 3.7 mg dm^–2 on a unit leaf area basis). Leaf area was largest when plants were grown under the intermediate PPFDs. Leaf density thickness was largest when plants were grown under the largest PPFDs. It is concluded that L. leucocephala shows extensive ability to acclimate to neutral shade, and could be considered a facultative shade plant.Abbreviations the initial slope of the photosynthesis vs PPFD curve - P_{n max} the light-saturated photosynthetic rate - PPFD photosynthetic photon flux density     

Respiration and oxygen transport functions of the blood from an intertidal fish,Helcogramma medium (Tripterygiidae)

Synopsis Aquatic and aerial oxygen uptake (̇O₂), ventilation frequency, and oxygen transport properties of the blood were determined for the intertidal fish Helcogramma medium. Ventilation frequency increased in response to decreased environmental PO₂ and aquatic ̇O₂ was maintained down to a critical PO₂ of 30–40 mm Hg. Below PO₂ 30 mm Hg fish intermittently gulped air and finally emerged into air at PO₂ 18 mm Hg. After 1 h exposure to air ̇O₂ decreased to 60% of the aquatic rate and this was accompanied by an increase in blood lactate. Aerobic expansibility was reduced in air (×1.2) compared to water (× 5.5). The Hb concentration was 0.47 ± 0.13 mmol 1^–1 and hematocrit 11.55 ± 3.61% indicating a moderate O₂-carrying capacity. Oxygen affinity was not especially high (P₅₀ = 19 mm Hg at pH 7.7 and 15°C) and ATP was the predominant acid-soluble phosphate regulating P₅₀. The equilibrium curve was essentially hyperbolic (Hill's n = 1.2) with a marked Bohr effect = –1.06) and Root effect (saturation depressed by 50% at pH7.1). The pattern of respiration and the respiratory properties of the blood together with observations of the behaviour of the fish during aerial exposure indicated that Helcogramma is adapted to living in a well-aerated environment yet can adequately tolerate short term exposure to low aquatic PO₂ or air.     

Effects of nitrite exposure on blood respiratory properties,acid-base and electrolyte regulation in the carp (Cyprinus carpio)

Summary Adult carp were subjected to 1 mM environmental nitrite for 48 h and nitrite uptake and changes in blood respiratory properties, extracellular electrolyte composition and acid-base status were examined.A constant influx of nitrite caused an accumulation of NO ₂ ^– in plasma to 5.4 mM in 48 h. The fraction of methaemoglobin rose with plasma [NO ₂ ^– ] to 83%, and the arterial oxygen content decreased to extremely low values. Arterial increased as a compensation to this O₂-shortage, whereas the O₂ saturation of the functional (unoxidized) haemoglobin decreased, revealing a reduction in its O₂ affinity.Blood haematocrit decreased as a result of red cell shrinkage, which caused very high red cell haemoglobin (Hb) concentrations. The erythrocytic nucleoside triphosphate (NTP) concentration showed a parallel increase whereby NTP/Hb, as well as the relative contributions of ATP and GTP to NTP, remained unchanged.Plasma [Cl^–] declined by 15 mM in 48 h, off-setting the plasma [NO ₂ ^– ] increase, minor changes in plasma [HCO ₃ ^– ] and a considerable increase in plasma [lactate]. Arterial pH and [HCO ₃ ^– ] rose slightly during the first 24 h of nitrite exposure, but returned to control values at 48 h. The rise in plasma [lactate] was not reflected in an extracellular metabolic acidosis. Plasma [K⁺] increased by 94% in 48 h, revealing an uncompensated extracellular hyperkalemia, whereas plasma [Na⁺] decreased, and plasma [Ca⁺⁺] was unchanged. Plasma osmolality remained essentially constant.The NO ₂ ^– accumulation could be reversed by transfer of the fish to NO ₂ ^– -free water, but nitrite off-loading was slower than the preceding NO ₂ ^– loading.Abbreviations Hb hemoglobin - NTP nucleoside triphosphate - Hct hematocrit - fractional saturation of Hb with oxygen     

Nystatin-, mycoheptin- and levorin-induced conductance in the membrane of frog skeletal muscle fibres

The effects of the polyene antibiotics nystatin (2 × 10^–5–10^–4 mol/l), mycoheptin (1.3 × 10^–6–10^–5 mol/l) and levorin (10^–8–5 × 10^–5 mol/l)on isolated frog skeletal muscle fibres and whole sartorius muscles of the frog have been investigated. Cation conductance was measured under current clamp conditions using a double sucrosegap technique. Cation effluxes were studied by means of flame emission photometry. All three antibiotics increased the cation conductance and efflux rates; however, differences between the polyenes were found in the steady state values of induced cation transport at a given concentration. The values of both induced conductance g_A and efflux rate constants K_A formed the following sequence: levorin > mycoheptin > nystatin, demonstrating a correlation with the order of antifungal activities. The dose-response curves of lg polyene-induced cation transport against lg of antibiotic concentration in our experiments had slope values which were much lower than those in bilayers: 1.7 and 1.3 for nystatin and mycoheptin, respectively, whereas the aromatic heptaene levorin had an even smaller concentration dependence. The decline in the equilibrium conductance caused by nystatin- and mycoheptin removal was very fast (during the first minute = 0.74 and 2.39 min, respectively). In contrast, levorin-induced conductance was irreversible. It is proposed that the processes which limit the rate of channel formation are different in biological and model membranes. Correspondence to: N. E. Shvinka