bluuebunny/crossref_metadata_2025 huggingface dataset:
A mysid shrimp carrying a pair of binoculars
Authors: Nilsson Dan-E. , Modlin Richard F.
Published: April 2021

Like other mysid shrimps, the tropical shallow-water species Dioptromysis paucispinosa possesses compound eyes of the refracting superposition type. In the rear of each eye, pointing backwards, is a single conspicuous facet almost three times the diameter of those in the rest of the eye. Underlying the large facet is an equally enlarged single crystalline cone, projecting an upright image onto a specialized retina of 120 densely packed and extremely narrow rhabdoms. This peculiar arrangement constitutes an acute zone which operates as a simple eye within a compound eye. Calculations of spatial sampling frequency and photon catch indicate that the centre of the acute zone resolves more than six times better than the normal eye, but it requires intensities more than a log unit higher – figures not unlike those of modern compact binoculars. The fact that the acute zone covers a visual field of 15–20°, with a large binocular overlap, strengthens the analogy with a pair of binoculars. The resolution of the acute zone is also remarkable in absolute terms: a rhabdom axis separation of 0.64° rivals foveal vision in large insects, although the entire eye of Dioptromysis measures only 0.4 mm. With the normal posture of the shrimp, the acute zone points backwards, about 12 ° above the horizon. Difficulties in understanding the animal’s use of such an acute zone were resolved by the discovery of large coordinated eye movements. The eyestalk can be rotated around its axis by at least 130 °. This makes the acute zone aim forwards and upwards, which is a more sensible direction for spotting and pursuing prey. The acute zone is probably held in the rest position aiming backwards only to avoid having an important part of the forward visual field constantly occupied by an eye region of inferior sensitivity.
Blood Sugar and the Follicles of Langerhans in the Ammocoete Larva
Authors: Barrington E. J. W.
Published: April 2021

Glandular follicles, first described by Langerhans, develop in the wall of the alimentary canal of the ammocoete larva at the point of junction of fore- and midgut, and have often been compared with the pancreas of higher forms. They have been re-examined histologically, using Helly’s fixative and the ‘Azan’ stain, and the view of some recent workers, that they have the appearance of endocrine structures, is confirmed. They comprise only one type of cell, however, which shows no decisive resemblance in staining reaction to any of the cell types characteristic of typical islet tissue.

The injection of glucose into ammocoetes usually produces a marked response in these cells, involving extensive vacuolization, while destruction of the follicles by cautery induces a significant rise in blood sugar. These reactions, which imply that the follicles are involved in carbohydrate metabolism, are similar to those associated with the B cells of islet tissue.

It is concluded that the evidence, while not yet complete, suggests that the follicles represent a primitive stage in the evolution of the endocrine component of the vertebrate pancreas, and it is pointed out that ‘follicles of Langerhans ‘would be an apt designation for them. Further work will be necessary to Clarify their relationship to the islets of Langerhans of higher forms.
The Temperature and Humidity Relations of the Cockroach
Authors: Gunn D. L. , Cosway C. A.
Published: April 2021

The carpet type of Barcroft respiration apparatus previously used by Gunn for cockroaches gives results comparable with those now obtained with a new basket type. Desiccated cockroaches use oxygen at the same rate per animal as undesiccated specimens. If, however, the rates are calculated with reference to the weight of the animal at the time of the experiment, since the desiccated animals tested had lost about 25 % of their original weight, their rates of oxygen consumption appeared to have gone up. Both normal and desiccated animals used oxygen slightly faster in moist air than in dry. Part of this increase must be attributed to a higher body temperature in moist air at 25° C. than in drier air at 25° C. Part of it may be due to greater activity in moist air than in dry, slight though the activity was in both cases. There is no reason to believe that, at a given body temperature, air humidity influences basal metabolic rate.
Shape Transformations in the Red Cells of Camels, Birds, Reptiles, Amphibia, and Fishes
Authors: Ponder Eric
Published: April 2021

The bearing of shape changes on the problem of red-cell structure is so great that we cannot afford to omit studying the transformations which occur in oval nucleated red cells in order to compare them with those in the discoidal non-nucleated red cells of man and of most mammals. The purpose of this paper, accordingly, is to give a description of the shape changes observed in the erythrocytes of camels, birds, reptiles, amphibians, and fishes.
Narcosis and Asphyxiation in Some Species and Mutants of Drosophila
Authors: Kalmus Hans
Published: April 2021

Narcosis and asphyxia in insects can be investigated by measuring the recovery time. This and other terms are defined, and suitable criteria of recovery are given. Simple techniques for the etherizing and gassing of Drosophila batches are described and the validity of the quantitative results obtained is shown. The recovery time is increased by the time of influx and by the concentration oj the narcotic. The shapes of the curves obtained in experimental Series are logarithmic (carbon dioxide asphyxiation), straight line (ether in some species), concave, convex or sigmoid (ether). It is suggested that the different forms of ether recovery curves are different parts of essentially similar curves, which one might explain by the joint action of two macrophases, one aqueous and one lipoid. Physiological factors determining recovery times are : (a) sex : females recover earlier from ether narcosis than males; (b) age: young flies recover earlier than older ones; (c) lack of food and moisture, which increases the recovery time ; and (d) chemical reaction: flies kept on acid food remain longer narcotized than flies-bred on an alkaline medium. Carbon dioxide lengthens recovery from ether narcosis and hydrocyanic acid immobilization when applied before the influx time and shortens it when applied during recovery-time. If administered during recovery, it also shortens the recovery from asphyxiation. Carbon monoxide and coal gas administered before narcotization can shorten the recovery time from ether narcosis. Under specified conditions corresponding to those, used during narcosis by Droso-phila-workers some differences in recovery time after etherization due to genetical differences could be established. Significant differences also exist between some Drosophila species, races and mutants in their resistance to carbon dioxide, asphyxiation and hydrocyanic acid.gas.
Scale effects on the stresses and safety factors in the wing bones of birds and bats
Authors: Kirkpatrick Sean J.
Published: April 2021

The effects of scale on the estimated stresses and safety factors in the humeri of several bird and bat species were investigated. This was accomplished by estimating the lift distribution across the wings at two extremes of flight, gliding flight and the downstroke in hovering, finding the center of lift on the wings at these two extremes and calculating the applied bending and twisting moments. This information, along with measurements of mechanically important morphological variables, allowed for estimates of bending and shearing stresses in the humeri for both gliding flight and on the downstroke in hovering. The stresses in flapping flight other than hovering should fall somewhere between these two values. It was found that the stresses in the humeri are not scale-dependent and that the bending stresses are slightly lower than those found in the limbs of terrestrial animals, while the shearing stresses are larger than those in terrestrial limbs. The breaking stress of bird and bat wing bone was also investigated. Both materials were found to have a lower breaking stress than that of typical long bone material. The ratio between the breaking stress of the material and the estimated stresses was defined as the safety factor. Bird humeri have safety factors that are generally greater than those of bat humeri. This is because bat bone has a lower breaking stress than does bird bone, although the estimated stresses in the wings are similar. The mean safety factor against failure due to bending in gliding flight was 6.63 for birds and 3.99 for bats. In hovering, the mean safety factors against failure due to bending were 2.22 for birds and 1.41 for bats. The safety factors against failure due to shearing stresses were estimated to be seven time greater than those against failure due to pure bending stresses.
Comparative analysis of hyperexcitability and synaptic facilitation induced by nerve injury in two populations of mechanosensory neurones of Aplysia californica
Authors: Clatworthy Andrea L. , Walters Edgar T.
Published: April 2021

Long-term effects of nerve injury on electrophysiological properties were compared in two populations of mechanosensory neurones in Aplysia californica: the J and K clusters in the cerebral ganglia and the VC clusters in the pleural ganglia. Following crush of cerebral nerves containing their axons, the cerebral J/K sensory neurones showed long-term changes that were quite similar to alterations previously described in the VC sensory neurones after either axonal injury or aversive learning. These changes include synaptic facilitation, an increase in soma excitability and spike duration, and a decrease in spike threshold and afterhyperpolarization. In addition, simultaneous crush of both the cerebral and pedal nerves in the same animals produced alterations in the cerebral J/K sensory neurones and pleural VC sensory neurones that were virtually identical. The incidence of hyperexcitability was the same in cerebral J/K and pleural VC sensory neurones when all their axons were crushed, even though the former population includes many neurones that probably have appetitive functions while the latter population appears to be made up exclusively of neurones with defensive functions. Long-term plasticity in both sensory populations failed to occur when nerves lacking axons of the tested neurones were crushed, even when the crush site was very close to the somata of the sensory neurones. This axonal specificity argues against a role for delayed activation of facilitatory interneurones in triggering the plasticity. Several observations are consistent with a triggering role for either (1) intracellular signals released directly by axonal injury or (2) extracellular signals released locally by other axons or injured support cells, or by immunocytes attracted to the injured site.
Blood pressure control in the antarctic fish Pagothenia borchgrevinki
Authors: Axelsson Michael , Davison Bill , Forster Malcolm , Nilsson Stefan
Published: April 2021

The mechanisms of cardiovascular control in the Antarctic fish Pagothenia borchgrevinki were investigated during rest and swimming exercise using pharmacological tools to reveal the nature of the control systems involved. Simultaneous and continuous recordings of ventral and dorsal aortic blood pressure, heart rate and ventral aortic blood flow (cardiac output) were made using standard cannulation procedures and a single-crystal Doppler flowmeter.

Exercise produced a clear and consistent decrease in dorsal aortic blood pressure caused by a decrease in systemic vascular resistance. At the same time, ventral aortic blood pressure increased owing to the combined effects of a markedly increased cardiac output (by about 80 %) and branchial vasoconstriction. Judged from the effects of the α-adrenoceptor antagonist prazosin, control of the branchial vasculature involves an α-adrenoceptor-mediated vasoconstriction, in addition to more traditional cholinergic vasoconstrictor and β-adrenoceptor-mediated dilatory mechanisms.

The range of heart rates is large, from 3–4 beats min-1 in individual fish during hypertensive bradycardia to about 28 beats min-1 after atropine treatment. Both chronotropic and inotropic effects are responsible for a marked increase in cardiac output during exercise. The increase in blood pressure caused by adrenaline injection was due largely to an increase in cardiac output, while direct effects on the systemic vasculature were small and transient. The increase in cardiac output, in turn, was due solely to an adrenergic stimulation of stroke volume. A barostatic bradycardia, often seen in other vertebrates in response to adrenaline injection, was absent and it is possible that a decrease in heart rate was offset by direct adrenergic stimulation of the heart.

Angiotensin II (Ang II) produced consistent hypertension by systemic vasoconstriction. In contrast to the effects of adrenaline injection, the hypertension caused by Ang II was accompanied by a marked bradycardia. This could be abolished by atropine, suggesting a cholinergic vagal reflex of the type found in other vertebrates.

Angiotensin I also caused an elevated blood pressure, and this effect was abolished by the angiotensin converting enzyme inhibitor enalapril, demonstrating elements of an angiotensin-related cardiovascular control system.
Evidence of regulatory mechanisms for the distribution of blood between the arterial and the venous compartments in the hagfish gill pouch
Authors: Sundin L. , Axelsson M. , Nilsson S. , Davison W. , Forster M. E.
Published: April 2021

Of the extant vertebrate animals, the hagfishes are generally considered to be the group which diverged first from the ancestral vertebrate lineage, although molecular sequence analysis has recently suggested that they form a monophyletic group with lampreys (Stock and Whitt, 1992). The circulatory system of hagfishes has features that have been described as ‘primitive’ (Burggren et al. 1985), but their gills are effective gas exchangers. The gills are contained within discrete muscular pouches, and the anatomy of the blood system and ventilatory ducts has an ideal countercurrent arrangement (Mallatt and Paulsen, 1986; Elger, 1987).
Motion analysis of escape movements evoked by tactile stimulation in the cockroach Periplaneta americana
Authors: Schaefer Paul L. , Kondagunta G. Varuni , Ritzmann Roy E.
Published: April 2021

The escape behavior of the American cockroach, Periplaneta americana, has provided a large amount of neuroethological data on the control of orientation movements. In the typical behavior, the animal responds to gentle wind puffs by turning away from the wind source and running (Camhi and Tom, 1978). However, cockroaches also escape in a directional manner in response to tactile stimuli (Comer et al. 1989, 1993). This additional category of escape response raises two important questions. Do the neural circuits for wind-and tactile-evoked escape responses converge, and if so where? At one extreme, the two behaviors may be under the control of completely separate circuits. Alternatively, the two sensory pathways could converge on a single set of controlling interneurons.
The relative contributions of red and white blood cells to whole-blood energy turnover in trout
Authors: Wang Tobias , Nielsen Ole B. , Lykkeboe Gunnar
Published: April 2021

Previous studies addressing energy turnover in fish blood have ignored the possible influence of white cells. The present investigation quantified the contribution of white and red cells to whole-blood energy turnover in trout (Oncorhynchus mykiss) before and after adrenergic stimulation. All experiments were carried out on cells kept in their native plasma. White cells were found to have an almost twenty times higher rate of oxygen consumption than red cells. Furthermore, white cells were responsible for essentially all whole-blood lactate production. Our data therefore show that white cells account for almost half of the energy turnover in trout blood. Adrenergic stimulation elicited a significant increase in total as well as ouabain-sensitive (a Na+/K+-ATPase inhibitor) red cell oxygen consumption. However, the ouabain-sensitive red cell oxygen consumption amounted to approximately 23 % of the total red cell oxygen consumption, regardless of adrenergic stimulation. Therefore, energy-consuming processes other than Na+/K+-ATPase activity are probably involved in the increased red cell oxygen uptake after adrenergic stimulation.
Mechanical Performance of anin SituPerfused Heart From the TurtleChrysemys ScriptaDuring Normoxia and Anoxia At 5°C and 15°C
Authors: Farrell A. P. , Franklin C. E. , Arthur P. G. , Thorarensen H. , Cousins K. L.
Published: April 2021

We developed an in situ perfused turtle (Chrysemys scripta) heart preparation to study its intrinsic mechanical properties at 5°C and 15°C using normoxic and anoxic perfusion conditions. The in situ preparation proved durable and stable. At 15°C and a spontaneous heart rate of 23.4 beats min−1, maximum stroke volume was 2.54 ml kg−1 body mass, maximum cardiac output was 62.5 ml min−1 kg−1 and maximum cardiac myocardial power output was 1.50 mW g−1 ventricular mass. There was good agreement between these values and those previously obtained in vivo. Furthermore, since the maximum stroke volume observed here was numerically equivalent to that observed in ventilating C. scripta in vivo, it seems likely that C. scripta has little scope to increase stroke volume to a level much beyond that observed in the resting animal through intrinsic mechanisms alone. The ability of the perfused turtle heart to maintain stroke volume when diastolic afterload was raised (homeometric regulation) was relatively poor.

At 5°C, the spontaneous heart rate (8.1 beats min−1) was threefold lower and homeometric regulation was impaired, but maximum stroke volume (2.25 ml kg−1) was not significantly reduced compared with the value at 15°C. The significantly lower maximum values for cardiac output (18.9 ml min−1 kg−1) and power output (0.39 mW g−1 ventricular mass) at 5°C were largely related to pronounced negative chronotropy with only a relatively small negative inotropy.

Anoxia had weak negative chronotropic effects and marked negative inotropic effects at both temperatures. Negative inotropy affected pressure development to a greater degree than maximum flow and this difference was more pronounced at 5°C than at 15°C. The maximum anoxic cardiac power output value at 15°C (0.77 mW g−1 ventricular mass) was not that different from values previously obtained for the performance of anoxic rainbow trout and hagfish hearts. In view of this, we conclude that the ability of turtles to overwinter under anoxic conditions depends more on their ability to reduce cardiac work to a level that can be supported through glycolysis than on their cardiac glycolytic potential being exceptional.
Characterisation of Large Second-Order Ocellar Neurones of the Blowfly Calliphora Erythrocephala
Authors: Simmons Peter J. , Jian Shi , Rind F. Claire
Published: April 2021

Blowflies have twelve large, second-order ocellar neurones (L-neurones) with axons in the single ocellar nerve. These neurones have fairly restricted arborizations in the posterior slope neuropile of the protocerebrum and cell bodies in the nerve, near to the fused ocellar retinae. Like ocellar L-neurones of other insects, or large second-order neurones of the fly compound eye, blowfly L-neurones hyperpolarise in response to increases in light intensity and depolarise in response to decreases in light intensity. Both polarities of response have a strong phasic component. Adaptation to sustained illumination shifts the intensity–response curve, with little change in its gradient. The maximum responses of blowfly L-neurones to sinusoidal changes in light intensity occur at stimulus frequencies of 5–10 Hz. Hyperpolarising an L-neurone with small currents causes an increase in input resistance. Larger hyperpolarising currents cause oscillations in the membrane potential. The amplitude of the oscillations increases with current strength. Repolarisation generates brief rebound spikes of variable amplitude. Injection of small hyperpolarising currents increases the amplitude of a response to a subsaturating pulse of light. This effect is not seen for saturating responses to light and is likely to be due to the increase in membrane resistance caused by hyperpolarisation.
Implications of Gill Arch Movements for Filter-Feeding: An X-Ray Cinematographical Study of Filter-Feeding White Bream (Blicca Bjoerkna) and Common Bream (Abramis Brama)
Authors: Den Berg Coen Van , Van Den Boogaart Jos G. M. , Sibbing Ferdinand A. , Osse Jan W. M.
Published: April 2021

Previous research shows that the reducible-channel model of filter-feeding can probably be applied to common bream, but not to white bream. According to this model, zooplankton are retained in the channels between the medial gill rakers; the mesh size of the sieve can be reduced by lowering the lateral rakers of the neighbouring gill arch into these channels. Gill arch movements may well disturb this mechanism; the depressed lateral gill rakers will move in and out of the medial channels and also shift out of their centre. We have quantified these disturbances by measuring the gill arch movements during filter-feeding in white bream and common bream, using dorsal X-ray films. In both species, the lateral rakers are long enough to bridge the gill slits. It was expected that common bream, which can reduce their channels, would have considerably less shift out of the channel centre than white bream, which cannot reduce their channels. However, the predicted shift is 40–50% of the channel width in white bream and 75% in common bream. A new, dynamic retention mechanism is proposed for common bream. According to this hypothesis, once a particle is trapped in a reduced channel, the channel walls release mucus and the particle becomes sticky. Hence, particles need to be retained mechanically only during part of the gulping cycle. According to the hypothesis, this is achieved by sideways rotation of the lateral rakers in combination with their tapering shape. Retention mechanisms with interdigitating rakers are expected chiefly in facultative filter-feeders, because such mechanisms are easily disturbed by gill arch movements.
Activation and Physiological Role of Na+/H+ Exchange in Lamprey (Lampetra Fluviatilis) Erythrocytes
Authors: Virkki Leila V. , Nikinmaa Mikko
Published: April 2021

The effects of intracellular acidification, osmotic shrinkage and (3-adrenergic stimulation on sodium transport across the membrane of lamprey (Lampetra fluviatilis) erythrocytes were investigated. Unidirectional ouabain-insensitive sodium flux, measured using radioactive 22Na, was increased markedly by intracellular acidification, to a lesser extent by osmotic shrinkage and only modestly by β-adrenergic stimulation. Na+/H+ exchange was activated in all of these cases. However, net sodium influx (and cell swelling caused by the influx of osmotically obliged water) was seen only in cells subjected to intracellular acidification. In contrast, practically no changes in red cell pH or in water or ion (Na+, K+ and Cl−) contents were seen after osmotic shrinkage or (3-adrenergic stimulation. Calculations of the [Na+]0/[Na+]i and [H+]0/[H+]i ratios across the erythrocyte membrane suggest that the virtual lack of net sodium movements in osmotically shrunken erythrocytes is due to the absence of a driving force for net transport of these ions via the Na+/H+ exchange pathway. It also appears that, in physiological conditions, the increase in the activity of the Na+/H+ exchanger by β-adrenergic stimulation is too small to mediate detectable net sodium transport.
Energy Metabolism by Trout Red Blood Cells: Substrate Utilisation
Authors: Pesquero J. , Roig T. , Bermudez J. , Sanchez J.
Published: April 2021

The present study investigates energy metabolism by trout red blood cells. It is shown that they are able to use pyruvate at physiological concentrations as an aerobic source of energy. Moreover, microcalorimetric data suggest that trout erythrocytes are also able to use internal substrates, at least when maintained in vitro. Although the actual nature of these substrates has not been elucidated, glycogen appears to be the most probable.

The relationship between heat dissipation and oxygen consumption suggests that most of the oxygen is used to oxidize substrates, and the inhibition of respiratory activity by antimycin A indicates that there is no substantial utilisation of non-respiratory oxygen. However, the oxygen uptake by these cells does not appear to be related to substrate utilisation, measured from transformation of labelled molecules (either pyruvate or glucose); this may be due to mixing of labelled compounds with non-labelled molecules in the intracellular pools, because of the low metabolic rate of these cells.
Metamorphic And Speed Effects On Hindlimb Kinematics During Terrestrial Locomotion In The Salamander Dicamptodon Tenebrosus
Authors: Ashley-Ross Miriam A.
Published: April 2021

The kinematics of the hindlimb during terrestrial treadmill locomotion in Dicamptodon tenebrosus were compared between larval and metamorphosed individuals at different speeds. Coordinates of marker points on the salamander’s midline, pelvic girdle and left hindlimb were digitized from high-speed videos (200 fields s−1). These yielded kinematic variables describing trunk flexion, pelvic girdle rotation, femoral protraction/retraction and knee flexion/extension. A three-way analysis of variance tested for mean differences among individuals, speeds and metamorphic stages for each variable. No significant overall effects of metamorphosis were found, although several variables showed significant stage × individual effects. Multivariate analyses revealed that the variance in kinematics of the larvae was significantly greater than that of the metamorphosed salamanders. Several variables showed significant speed effects or strong trends, among them stride length (increases with speed), cycle duration (decreases), contact interval (decreases) and phase variables describing the relative timing between minimum/maximum angles and the beginning of stance/swing phase. Such changes with speed are consistent with those shown for diverse arthropods and tetrapods and suggest that changes in stride length and timing events during a stride represent a general mechanism for effecting an increase in locomotor speed.
Effects of Muscle Length on the Emg–Force Relationship of the Cat Soleus Muscle Studied Using Non-Periodic Stimulation of Ventral Root Filaments
Authors: Guimaraes A. C. , Herzog W. , Hulliger M. , Zhang Y. T. , Day S.
Published: April 2021

The effects of changing the length of the cat soleus muscle on electromyographic (EMG) signals, muscle force and the corresponding EMG–force relationship were assessed using distributed stimulation of ten ventral root filaments and irregular interpulse intervals. EMG–force relationships were first determined for four muscle lengths using a protocol of simultaneous addition and rate modulation of ventral root filaments. In the second test, three submaximal levels of stimulation were applied at eight muscle lengths. EMG signals were obtained using surface and wire electrodes, and force was measured using a strain transducer. For most muscle lengths, the relationships between integrated EMG and mean force obtained using wire and surface electrodes were sigmoid with a linear intermediate region. The effects of muscle length on EMG signals were likely to be associated with movement of the recording electrodes relative to each other and to the active motor units. Mean forces increased with increasing muscle length and with increasing levels of stimulation. Mean force–length relationships obtained using submaximal stimulation were not simply scaled down versions of the force–length relationship obtained using supramaximal stimulation of the soleus nerve, but appeared to be shifted towards longer muscle lengths.
Na+/Ca2+ Antiport in the Mammalian Heart
Authors: Reeves John P. , Condrescu Madalina , Chernaya Galina , Gardner Jeffrey P.
Published: April 2021

The cardiac Na+/Ca2+ antiporter moves 3 Na+ across the plasma membrane in exchange for a single Ca2+ moving in the opposite direction. It is the principal Ca2+ efflux mechanism in myocardial cells; however, it also contributes to Ca2+ influx under certain conditions. It is particularly abundant in the heart, but is also expressed in other tissues such as smooth and skeletal muscle, the kidney and the brain. The cardiac antiporter itself is a protein of 938 amino acids, with a cleaved NH2-terminal signal sequence, 11 putative transmembrane segments and a large hydrophilic domain of 520 amino acids between the fifth and sixth transmembrane segments. Alternative mRNA splicing mechanisms generate tissue-specific isoforms in a limited region within the hydrophilic domain. Most of the hydrophilic domain can be deleted without altering the kinetics of the transport reaction; the regulatory properties of the antiporter are markedly affected by this deletion however. Two different modes of regulation of antiport activity have been characterized and appear to involve two different inactive states of the carrier. The first is promoted by the presence of cytosolic Na+ in the absence of ATP and the second is promoted by the absence of cytosolic Ca2+. ATP-dependent regulation of antiport activity may involve interactions with the cellular cytoskeleton, since the effects of ATP depletion can be mimicked by cytochalasin D. Ca2+-dependent regulation of antiport activity appears to involve the interaction of cytosolic Ca2+ with two acidic amino acid sequences within a limited region of the hydrophilic domain.
Endosomal Accumulation of pH Indicator Dyes Delivered as Acetoxymethyl Esters
Authors: Slayman Clifford L. , Moussatos Vasiliana V. , Webb Watt W.
Published: April 2021

Intracellular distributions of the putative cytosolic pH indicator dyes BCECF [2′,7′-bis-(2-carboxyethyl)-5(and 6)-carboxyfluorescein], C.SNARF [5(and 6)-carboxy-seminaphthorhodafluor-1], and C.SNARF-calcein have been examined in Neurospora crassa and in murine fibroblasts (NIH-3T3 cells) under conditions in which both kinds of cells produce visible microscopic vacuoles. All three dyes were administered in electroneutral forms, with the hydroxyl and carboxyl groups esterified (designated as -AM esters). As judged qualitatively from fluorescence levels, hydrolytic derivatives of the two heavily esterified dyes (BCECF-AM and C.SNARF-calcein-AM) accumulated in the vacuoles after exposures of approximately 15 min or more, while the simpler dye (C.SNARF-AM) and its derivatives were almost excluded from visible vacuoles. Fluorescence from this dye, alone among the three, also washed out of Neurospora rapidly upon removal of extracellular dye. There was no evidence for stable accumulation of any of the dyes in cytosol per se. For BCECF(-AM), comparison of the distribution of fluorescence with the size distribution of vacuoles in Neurospora strongly suggests that the dyes are also accumulated by endomembranal vesicles (EMVs) which lie below the limit of resolution in the light microscope, and the same inference can be drawn for the fibroblasts. Uptake of -AM dyes by EMVs, including frank vacuoles, probably results from the action of intravesicular esterases, following diffusional entry of lipophilic neutral molecules or partially de-esterified anions. Calculations of actual cytosolic pH values, or even changes of pH, based on intracellular fluorescence of these dyes, clearly depend upon quantitative knowledge of the subcellular dye distribution. Therefore, until the problem is reliably solved of how to visualize submicroscopic vesicles in living cells, the safest approach to the use of BCECF, C-SNARF and their congeners for cytosolic pH measurement would be to devise methods for coaxing uptake of the ionic forms of these dyes and to abandon use of the esterified forms.
Molecular Physiology of the Na+/H+ Antiporter in Escherichia Coli
Authors: Padan Etana , Schuldiner Shimon
Published: April 2021

All living cells maintain an inwardly directed Na+ gradient and a constant intracellular pH. Na+/H+ antiporters have been assigned an essential role in these homeostatic mechanisms in all cells. In Escherichia coli, two Na+/H+ antiporter genes, nhaA and nhaB, have been cloned. Deletion of either one or both showed that NhaA is essential for adaptation to high salinity, for growth at alkaline pH in the presence of Na+ and for challenging Li+ toxicity. NhaB confers tolerance to low levels of Na+ and becomes essential when the activity of NhaA limits growth.

The adaptive response to Na+ is mediated by the positive regulator nhaR, which transduces the signal (intracellular Na+) to expression of the nhaA gene. We have identified Glu-134 of NhaR as part of the ‘Na+ sensor’ of NhaA.

In agreement with the role of NhaA in pH homeostasis, its Na+-dependent expression is enhanced at alkaline pH. Reconstitution of pure NhaA and NhaB in proteoliposomes demonstrates that, whereas both are electrogenic (the H+/Na+ stoichiometry of NhaA is 2), only NhaA is pH-dependent, increasing its activity 1000-fold between pH 7 and 8.5. Mutating all the histidines of NhaA shows that His-226 is part of the ‘pH sensor’ of NhaA.
Bacterial Anion Exchange: Reductionist and Integrative Approaches to Membrane Biology
Authors: Maloney Peter C. , Yan Run-Tao , Abe Keietsu
Published: April 2021

Studies of two different bacterial anion exchange proteins (antiporters) led us to conclude that both reductionist and integrative approaches contribute to progress in understanding membrane biology. We have used a reductionist perspective in applying cysteine scanning mutagenesis to probe individual amino acid positions of UhpT (uptake of hexose phosphate transporter), the carrier responsible for transport of glucose 6-phosphate by Escherichia coli. This work has established experimental criteria that should allow one to identify and localize the translocation pathway in such membrane proteins. An integrative view is exemplified by work with OxlT (oxalate transporter), the carrier used by an anaerobe Oxalobacter formigenes to catalyze the antiport of divalent oxalate and monovalent formate. The activity of OxlT is functionally coordinated with that of a cytosolic oxalyl decarboxylase; together, these vectorial and scalar activities constitute a metabolic proton pump, allowing O. formigenes to display decarboxylative phosphorylation. The role played by OxlT argues that membrane carriers can assume unanticipated emergent properties when their biochemical functions are properly articulated in relation to other aspects of cell function.
Hexose/H+ Symporters in Lower and Higher Plants
Authors: Caspari Thomas , Will Andreas , Opekarová Miroslava , Sauer Norbert , Tanner Widmar
Published: April 2021

A well-studied transporter of plant cells is the hexose/H+symporter of the unicellular alga Chlorella kessleri. Its properties, studied in vivo, are briefly summarized. In part, they are atypical and it has been suggested that this porter acts in an asymmetric way. Three genes coding for Chlorella hexose transport activity have been identified (HUP1, HUP2 and HUP3). HUP1 cDNA expressed in a mutant of Schizosaccharomyces pombe not transporting any D-glucose has been studied in detail. Several mutants with changed Km values for substrate were obtained, some by random polymerase chain reaction mutation and selection for decreased sensitivity towards the toxic sugar 2-deoxyglucose, some by site-directed mutagenesis. The amino acids affected clustered in the centre of the putative transmembrane helices V, VII and XI. Large families of hexose transporter genes are found in higher plants (Arabidopsis, Chenopodium, Ricinus). Their functional role is discussed. Finally, the progress made in studying plant transporters in a vesicle system energized by cytochrome c oxidase is summarized.
Thermodynamics of Symport and Antiport Catalyzed by Cloned or Native Transporters
Authors: Gerencser George A. , Stevens Bruce R.
Published: April 2021

Thermodynamic measurements are required to confirm whether cloned transport-associated proteins in a membrane truly constitute a functional transport system. Symport or antiport, catalyzed by native systems or by cloned proteins in membranes, can lead to steady-state intracellular accumulation of solute when the electrochemical potentials of activator ion and solute are energetically coupled. Secondary active transport can occur if an appropriate physical coupling mechanism exists in the membrane. Driving forces for secondary active transport are ultimately established by primary active transport or respiration. Steep steady-state gradients of solute can be maintained when the ion:solute coupling ratio is greater than one and/or when coupling includes an electrical component. Although the steady-state accumulation of substrate is independent of the exact physical mechanism of transport, non-equilibrium and equilibrium transport kinetics aid in interpreting the rate, direction (symport versus antiport) and control of ion-coupled flux across a membrane. In some cases, the activator ion’s chemical gradient alone is energetically adequate to maintain steady-state intracellular accumulation of solute, as demonstrated in invertebrate epithelial cells. To interpret accumulation ratios accurately, it is necessary to measure the intracellular activity coeffients for ions. For example, liquid ion-exchange microelectrode measurements demonstrate that over 30% of intracellular Na+ can be sequestered in epithelial cells.
The Effect of ATP-Sensitive Potassium Channel Modulation on Heart Rate in Isolated Muskrat and Guinea Pig Hearts
Authors: Streeby Daniel R. , McKean Thomas A.
Published: April 2021

Muskrats (Ondontra zibethicus) are common freshwater diving mammals exhibiting a bradycardia with both forced and voluntary diving. This bradycardia is mediated by vagal innervation; however, if hypoxia is present there may be local factors that also decrease heart rate. Some of these local factors may include ATP-sensitive potassium channel activation and extracellular accumulation of potassium ions, hydrogen ions and lactate. The purpose of this study was to investigate the role of these factors in the isolated perfused hearts of muskrats and of a non-diving mammal, the guinea pig. Although lactate and proton administration reduced heart rate in isolated muskrat and guinea pig hearts, there was no difference in the response to lactate and proton infusion between the two species. Muskrat hearts were more sensitive to the heart-rate-lowering effects of exogenously applied potassium than were guinea pig hearts. Early increases in extracellular potassium concentration during hypoxia are thought to be mediated by the ATP-sensitive potassium channel. Activation of these channels under normoxic conditions had a mildly negative chronotropic effect in both species; however, activation of these channels with Lemakalim under hypoxic conditions caused the guinea pig heart to respond with an augmented bradycardia similar to that seen in the hypoxic muskrat heart in the absence of drugs. Inhibition of these channels by glibenclamide during hypoxia was partially successful in blocking the bradycardia in guinea pig hearts, but inhibition of the same channels in hypoxic muskrat hearts had a damaging effect as two of five hearts went into contracture during the hypoxia. Thus, although ATP-sensitive potassium channels appear to have a major role in the bradycardia of hypoxia in guinea pigs, the failure to prevent the bradycardia by inhibition of these channels in muskrat hearts suggests that multiple factors are involved in the hypoxia-induced bradycardia in this species.
Spontaneous Swimming Activity of Atlantic Cod Gadus Morhua Exposed to Graded Hypoxia at Three Temperatures
Authors: Schurmann Henrik , Steffensen John Fleng
Published: April 2021

The spontaneous swimming activity of Atlantic cod Gadus morhua was investigated at graded levels of hypoxia at three temperatures (5, 10 and 15°C) by using a computerized system monitoring animal activity. The fish were tested individually, and swimming distance was used as a measure of activity. No significant effect of temperature on swimming distance in normoxic water was found. At all temperatures, activity level decreased with decreasing oxygen saturation. Swimming behaviour at normoxia and 50% and 25% oxygen saturation is described. No apparent avoidance of hypoxic water was found based on the distribution of swimming speeds and turning angles. The possible benefits of a decreased activity level in a hypoxic environment are discussed.
Respiratory Rhythm In The Isolated Central Nervous System Of Newborn Opossum
Authors: Zou Dong-Jing
Published: April 2021

Respiratory activity was recorded from spinal ventral roots in the isolated intact central nervous system (CNS) of newborn opossum, Monodelphis domestica. These signals occurred in synchrony with movements of the ribs and the electromyogram (EMG) recorded from the intercostal muscles during inspiration. Rhythmical activity could be recorded for more than 6 h in acute preparations. The rhythm-generating region was shown to be located in the lower brain stem by perfusing different CNS regions with medium containing 20 mmol l−1 Mg2+, which blocks synaptic transmission reversibly in the opossum CNS. The conclusion that respiration was generated by neurones in the lower brain stem was further confirmed by selective ablation of part of the CNS. Recordings were made from 128 neurones in the respiratory region of the lower brain stem with activity related to the respiratory rhythm. They consisted of two inspiratory groups and two expiratory groups. In the groups of inspiratory units, recordings were made from 69 early inspiratory and 38 inspiratory units. In the groups of expiratory units, recordings were made from 17 post-inspiratory and 4 expiratory units. The sites of 22 respiratory neurones were marked in 4-day-old animals by injecting Pontamine Sky Blue. These neurones were distributed from 175 μm anterior to 525 μm posterior to the obex, from 225 to 450 μm lateral to the midline and from 175 to 425 μm deep to the ventral surface of the brain stem. The respiratory rhythm recorded in the isolated CNS was influenced by pH and neurotransmitters. The respiratory rate decreased by about 26% at high pH (7.7) and increased by about 33% at low pH (7.1). Bath application of noradrenaline (30– 100 μmol l−1) decreased the respiratory rate and increased the amplitude of the rhythmic bursts significantly. All these effects were reversible. The results presented here indicate that the isolated intact CNS of newborn opossum offers advantages for exploring mechanisms responsible for generating the respiratory rhythm.
Regulation of Feeding Behavior in Adult Drosophila Melanogaster Varies With Feeding Regime and Nutritional State
Authors: Edgecomb Robert S. , Harth Cara E. , Schneiderman Anne M.
Published: April 2021

The regulation of feeding behavior in adult Drosophila melanogaster includes such elements as ingestion responsiveness, volume ingested in a single meal, food storage in the crop and rate of defecation. Our results suggest that feeding behavior varies in a manner dependent on feeding regime (food-deprived or ad-libitum-fed) and nutritional state. Fed flies that are subsequently food-deprived become increasingly more responsive to food stimuli over time and, when offered 1% agar diets containing different concentrations of sucrose, ingest greater amounts of diets that have higher sucrose concentrations. When fed ad libitum for 72 h on these same diets, D. melanogaster maintained much smaller crops on average than food-deprived flies fed a single meal. Additionally, ad-libitum-fed flies are grouped into two categories depending on the concentration of sucrose in the diet. Flies fed for 72 h on 1% agar diets having 50 mmol l−1 sucrose or more are not affected by the concentration of sucrose in the diet, while flies fed on diets of 15 or 25 mmol l−1 sucrose increase ingestion responsiveness, crop size and the rate of defecation with decreasing concentrations of sucrose in the diet. Flies fed on even lower sucrose concentrations (5 or 10 mmol l−1 sucrose) for 27–72 h exhibit both a shift over time to larger crop sizes and increased mortality over those of flies fed 15 mmol l−1 sucrose. These data suggest that flies fed ad libitum are capable of modulating their feeding behavior in response to their nutritional state.
Dynamic and Static Stability in Hexapedal Runners
Authors: Ting L. H. , Blickhan R. , Full R. J.
Published: April 2021

Stability is fundamental to the performance of terrestrial locomotion. Running cockroaches met the criteria for static stability over a wide range of speeds, yet several locomotor variables changed in a way that revealed an increase in the importance of dynamic stability as speed increased. Duty factors (the fraction of time that a leg spends on the ground relative to the stride period) decreased to 0.5 and below with an increase in speed. The duration of double support (i.e. when both tripods, or all six legs, were on the ground) decreased significantly with an increase in speed. All legs had similar touch-down phases in the tripod, but the shortest leg, the front one, lifted off before the middle and the rear leg, so that only two legs of the tripod were in contact with the ground at the highest speeds. Per cent stability margin (the shortest distance from the center of gravity to the boundaries of support, normalized to the maximum possible stability margin) decreased with increasing speed from 60% at 10 cm s−1 to values less than zero at speeds faster than 50 cm s−1, indicating instances of static instability at fast speeds. The center of mass moved rearward or posteriorly with respect to the base of support as speed increased. Moments about the center of mass, as shown by the center of pressure (the equivalent of a single ‘effective’ leg), were variable, but were balanced by opposing moments over a stride. Thus, hexapods can exploit the advantages of both static and dynamic stability. Static or quasi-static assumptions alone were insufficient to explain straight-ahead, constant-speed locomotion and may hinder discovery of behaviors that are dynamic, where kinetic energy and momentum can act as a bridge from one step to the next.
Calcium Channel Currents in Cultured Pars Intercerebralis Neurosecretory Cells of Adult Locusta Migratoria
Authors: Bickmeyer Ulf , Rössler Wolfgang , Wiegand Herbert
Published: April 2021

The medial neurosecretory cells (MNSCs) of the pars intercerebralis in the brain of insects release various hormonal factors that control essential physiological and developmental functions such as moulting, reproduction and metabolism (Wigglesworth, 1940; Girardie, 1966; Goldsworthy, 1969), and these cells are therefore of considerable biological significance. A culture system for locust embryonic pars intercerebralis neurosecretory cells has recently been developed (Vanhems et al. 1993), and Rössler and Bickmeyer (1993) have established an in vitro system for growing larval and adult medial neurosecretory cells. Calcium plays an important role in neural physiology: neurosecretion depends on calcium influx into the cells and calcium currents carry the rising phase of action potentials in different types of insect neurones (Orchard, 1976; Pitman, 1979); calcium also mediates other ionic currents (Thomas, 1984). It is therefore of considerable interest to characterize the types of calcium channel currents found in locust neurosecretory neurones.