bluuebunny/crossref_metadata_2025 huggingface dataset:
Biogenesis and Function of the Yeast Plasma-Membrane H+-ATPase
Authors: Ambesi Anthony , Miranda Manuel , Petrov Valery V. , Slayman Carolyn W.
Published: April 2021

One of the most abundant proteins in the yeast plasma membrane is the P-type H+-ATPase that pumps protons out of the cell, supplying the driving force for a wide array of H+-dependent cotransporters. The ATPase is a 100 kDa polypeptide, anchored in the lipid bilayer by 10 transmembrane α-helices. It is structurally and functionally related to the P-type Na+,K+-, H+,K+- and Ca2+-ATPases of animal cells and the H+-ATPases of plant cells, and it shares with them a characteristic reaction mechanism in which ATP is split to ADP and inorganic phosphate (Pi) via a covalent β-aspartyl phosphate intermediate. Cryoelectron microscopic images of the H+-ATPase of Neurospora crassa and the sarcoplasmic reticulum Ca2+-ATPase of animal cells have recently been obtained at 8 nm resolution. The membrane-embedded portion of the molecule, which presumably houses the cation translocation pathway, is seen to be connected via a narrow stalk to a large, multidomained cytoplasmic portion, known to contain the ATP-binding and phosphorylation sites. In parallel with the structural studies, efforts are being made to dissect structure/function relationships in several P-type ATPases by means of site-directed mutagenesis. This paper reviews three phenotypically distinct classes of mutant that have resulted from work on the yeast PMA1 H+-ATPase: (1) mutant ATPases that are poorly folded and retained in the endoplasmic reticulum; (2) mutants in which the conformational equilibrium has been shifted from the E2 state, characterized by high affinity for vanadate, to the E1 state, characterized by high affinity for ATP; and (3) mutants with altered coupling between ATP hydrolysis and proton pumping. Although much remains to be learned before the transport mechanism can be fully understood, these mutants serve to identify critical parts of the polypeptide that are required for protein folding, conformational change and H+:ATP coupling.
Assembly and Regulation of the Yeast Vacuolar H+-ATPase
Authors: Kane Patricia M. , Parra Karlett J.
Published: April 2021

The yeast vacuolar H+ -ATPase (V-ATPase) consists of a complex of peripheral subunits containing the ATP binding sites, termed the V1 sector, attached to a complex of membrane subunits containing the proton pore, termed the Vo sector. Interaction between the V1 and Vo sectors is essential for ATP-driven proton transport, and this interaction is manipulated in vivo as a means of regulating V-ATPase activity. When yeast (Saccharomyces cerevisiae) cells are deprived of glucose for as little as 5 min, up to 75 % of the assembled V-ATPase complexes are disassembled into cytoplasmic V1 sectors and membrane-bound Vo sectors. Remarkably, this disassembly is completely reversible. Restoration of glucose to the growth medium results in quantitative reassembly of the disassembled complexes in as little as 5 min, even in the absence of any new protein synthesis. Cells also appear to regulate the extent of V1 Vo assembly on a long-term basis. Yeast cells grown for extended periods in a poor carbon source contain a high proportion of free V1 and Vo sectors, and these sectors remain poised for reassembly when growth conditions improve. Parallel experiments on the Manduca sexta V-ATPase suggest that reversible disassembly may be a general regulatory mechanism for V-ATPases. These results imply that V-ATPases are surprisingly dynamic structures, and their unique ‘regulated instability’ raises a number of interesting physiological and structural questions. How are extracellular conditions such as carbon source communicated to V-ATPase complexes present on intracellular membranes? How are such major structural changes in the V-ATPase generated and how are V1 sectors ‘silenced’ in vivo to prevent unproductive hydrolysis of cytoplasmic ATP by the dissociated enzyme? We are addressing these questions using a combination of genetic and biochemical approaches.
The Cellular Biology of Proton-Motive Force Generation by V-ATPases
Authors: Nelson Nathan , Perzov Natalie , Cohen Adiel , Hagai Keren , Padler Vered , Nelson Hannah
Published: April 2021

The vacuolar H+-ATPase (V-ATPase) is one of the most fundamental enzymes in nature. It functions in almost every eukaryotic cell and energizes a wide variety of organelles and membranes. In contrast to F-ATPases, whose primary function in eukaryotic cells is to form ATP at the expense of the proton-motive force, V-ATPases function exclusively as ATP-dependent proton pumps. The proton-motive force generated by V-ATPases in organelles and across plasma membranes of eukaryotic cells is utilized as a driving force for numerous secondary transport processes. The enzyme is also vital for the proper functioning of endosomes and the Golgi apparatus. In contrast to yeast vacuoles, which maintain an internal pH of approximately 5.5, it is believed that the vacuoles of lemon fruit may have a pH as low as 2. Similarly, some brown and red algae maintain an internal pH as low as 1 in their vacuoles. It was yeast genetics that allowed the identification of the special properties of individual subunits and the discovery of the factors that are involved in V-ATPase biogenesis and assembly.

Null mutations in genes encoding V-ATPase subunits of Saccharomyces cerevisiae result in a phenotype that is unable to grow at high pH and is sensitive to high and low metal-ion concentrations. Treatment of these null mutants with ethyl methanesulphonate causes mutations that suppress the V-ATPase null phenotype, and these cells are able to grow at pH 7.5. The suppressor mutants were denoted as svf (Suppressor of V-ATPase Function). The svf mutations are recessive: crossing the svf mutants with their corresponding V-ATPase null mutants resulted in diploid strains that were not able to grow at pH 7.5. A novel gene family in which null mutations cause pleiotropic effects on metal-ion resistance or on the sensitivity and distribution of membrane proteins in different targets was discovered. We termed this gene family VTC (Vacuolar Transporter Chaperon) and discovered four genes in S. cerevisiae that belong to the family. Inactivation of one of them, VTC1, in the background of V-ATPase null mutations resulted in an svf phenotype that was able to grow at pH 7.5. Apparently, Vtc1p is one of a few membrane organizers that determine the relative amounts of different membrane proteins in the various cellular membranes. We utilize the numerous yeast mutants generated in our laboratory to identify the specific organelle whose acidification is vital. The interaction between V-ATPase and the secretory pathway is investigated.
The Energetic Cost of Short Flights in Birds
Authors: Nudds Robert L. , Bryant David M.
Published: April 2021

Many small birds perform short flights, for which take-offs, ascents and descents form a large component of the total flight time and which are characterised by low airspeeds. Using the doubly-labelled water technique, zebra finches Taeniopygia guttata engaging in repeated short flights were found to expend 13.65 kJ more than ‘non-flying’ controls, which equated to a flight expenditure of 27.8 times their basal metabolic rate. This is over three times the predicted flight expenditure derived from existing aerodynamic models. These data were used to determine a coefficient (0.11) for converting the mechanical power derived from aerodynamic models into metabolic power. An equation is presented, based on body mass, which can be used to predict the costs of short flights in ecological and behavioural studies of birds.
Behaviour-Locked Signal Analysis Reveals Weak 200–300 Hz Comb Vibrations During the Honeybee Waggle Dance
Authors: Nieh James C. , Tautz Jürgen
Published: April 2021

Waggle-dancing honeybees produce vibratory movements that may facilitate communication by indicating the location of the waggle dancer. However, an important component of these vibrations has never been previously detected in the comb. We developed a method of fine-scale behavioural analysis that allowed us to analyze separately comb vibrations near a honeybee waggle dancer during the waggle and return phases of her dance. We simultaneously recorded honeybee waggle dances using digital video and laser-Doppler vibrometry, and performed a behaviour-locked Fast Fourier Transform analysis on the substratum vibrations. This analysis revealed significantly higher-amplitude 200–300 Hz vibrations during the waggle phase than during the return phase (P=0.012). We found no significant differences in the flanking frequency regions between 100–200 Hz (P=0.227) and 300–400 Hz (P=0.065). We recorded peak waggle phase vibrations from 206 to 292 Hz (244±28 Hz; mean ± S.D., N=11). The maximum measured signal − noise level was +12.4 dB during the waggle phase (mean μ5.8±2.7 dB). The maximum vibrational velocity, calculated from a filtered signal, was 128 µm s−1 peak-to-peak, corresponding to a displacement of 0.09 μm peak-to-peak at 223 Hz. On average, we measured a vibrational velocity of 79±28 μm s−1peak-to-peak from filtered signals. These signal amplitudes overlap with the detection threshold of the honeybee subgenual organ.
Ontogenetic Changes in Visual Sensitivity of The Parasitic Salmon Louse Lepeophtheirus Salmonis
Authors: Flamarique Iñigo Novales , Browman Howard I. , Bélanger Marise , Boxaspen Karin
Published: April 2021

The salmon louse, Lepeophtheirus salmonis, is an ectoparasitic copepod of salmonid fishes whose life cycle involves two broadly defined, free-living larval stages, the nauplius and the copepodid. After settling on a host, the copepodid goes through various transformations to become a mobile adult. We recorded swimming responses of free-swimming salmon lice at the naupliar, copepodid and adult stages to the onset (ON) and offset (OFF) of lights of varying spectral irradiance and polarization. Nauplii showed a prominent swim-up OFF response across the spectrum 352–652 nm, but no ON response. Copepodids exhibited a swim-up ON response and a passive (sinking) OFF response across the same spectral range. Adults showed active swim-up responses to both ON and OFF stimuli, although the OFF response was proportionately stronger. The spectral range of the adult ON and OFF responses was the same as that of the copepodids and slightly greater than that of the nauplii, which did not exhibit responses at 652 nm. The absolute sensitivity of copepodids under white light (approx. 10−13 photons m2 s1) was higher than that of nauplii (approx. 10−17 photons−1 m2 s, OFF response) and that of adult female lice (approx. 10−14 photons−1 m2 s). This suggests that the naupliar visual system is best suited for detection of shadows (e.g. the host) under a bright light field (daylight hours), while copepodids and adults may be more specialized for host detection at crepuscular periods and during the night, when light levels are low. None of the developmental stages responded to the rotation of the plane of polarized light or exhibited any difference in directed response when polarized light was used in place of diffuse light.
Ventilation And Gas Exchange During Treadmill Locomotion in The American Alligator (Alligator Mississippiensis)
Authors: Farmer Colleen G. , Carrier David R.
Published: April 2021

A number of anatomical characters of crocodilians appear to be inconsistent with their lifestyle as sit-and-wait predators. To address this paradoxical association of characters further, we measured lung ventilation and respiratory gas exchange during walking in American alligators (Alligator mississippiensis). During exercise, ventilation consisted of low-frequency, large-volume breaths. The alligators hyperventilated severely during walking with respect to their metabolic demands. Air convection requirements were among the highest and estimates of lung PCO2 were among the lowest known in air-breathing vertebrates. Air convection requirements dropped immediately with cessation of exercise. These observations indicate that the ventilation of alligators is not limited by their locomotor movements. We suggest that the highly specialized ventilatory system of modern crocodilians represents a legacy from cursorial ancestors rather than an adaptation to a lifestyle as amphibious sit- and-wait predators.
Octopamine Mimics the Effects of Parasitism on the Foregut of the Tobacco Hornworm Manduca Sexta
Authors: Miles Carol I. , Booker Ronald
Published: April 2021

The parasitic braconid wasp Cotesia congregata lays its eggs inside the body of the larval stage of its host, the moth Manduca sexta. The Cotesia congregata larvae develop within the hemocoel of their host until their third instar, when they emerge and spin cocoons and pupate on the outer surface of the caterpillar. From this time until their death approximately 2 weeks later, the Manduca sexta larvae show striking behavioral changes that include dramatic declines in spontaneous activity and in the time spent feeding.

Coincident with these behavioral changes, it is known that octopamine titers in the hemolymph of the host become elevated by approximately 6.5-fold. Octopamine is an important modulator of neural function and behavior in insects, so we examined hosts for neural correlates to the behavioral changes that occur at parasite emergence. We found that, in addition to the changes reported earlier, after parasite emergence (post-emergence), Manduca sexta larvae also showed marked deficits in their ability to ingest food because of a disruption in the function of the frontal ganglion that results in a significant slowing or the absence of peristaltic activity in the foregut. This effect could be produced in unparasitized fifth-instar larvae by application of blood from post-emergence parasitized larvae or of 10−6 mol l−1 D,L-octopamine (approximately the level in the hemolymph of post-emergence larvae). In contrast, blood from parasitized larvae before their parasites emerge or from unparasitized fifth-instar larvae typically had no effect on foregut activity. The effects of either post-emergence parasitized blood or 10−6 mol l−1 octopamine could be blocked by the octopamine antagonists phentolamine (at 10−5 mol l−1) or mianserin (at 10−7 mol l−1).
Skin Temperatures During Free-Ranging Swimming And Diving In Antarctic Fur Seals
Authors: Boyd I. L.
Published: April 2021

This study tests the hypothesis that an endothermic homeotherm should minimise heat flux in cold polar waters by minimising skin temperature. Temperature variability was measured at the surface of the skin of three Antarctic fur seals (Arctocephalus gazella) at intervals of 2 s over a total of 9.7 days while they were swimming and diving freely in polar waters at temperatures of 1.5–4 °C. The temperature difference (ΔT) between skin on the dorsal thorax and the water varied from more than 20 °C to close to equality over periods of less than 1 h. Shorter-term variations in ΔT of up to 5 °C occurred in association with diving, although these types of variations also occurred without diving. In general, ΔT began to decline during the descent phase of a dive and began to increase again during the ascent or at the end of the dive. One of the three individuals examined showed little variation in ΔT, which remained low (approximately 3 °C) throughout the experiment. In the other two fur seals, ΔT tended to decline during periods of sustained diving and usually increased during periods spent at the surface. Mean calculated heat flux varied from 95 to 236 W m−2 depending on the individual. Metabolic rates based on these calculated heat fluxes were towards the lower end of those measured in previous studies using different methodologies. The study has shown that Antarctic fur seal skin temperature is highly dynamic and suggests that the thoracic surface is an organ used for active thermoregulation.
Hydrodynamic Drag In Steller Sea Lions (Eumetopias Jubatus)
Authors: Stelle Lei Lani , Blake Robert W. , Trites Andrew W.
Published: April 2021

Drag forces acting on Steller sea lions (Eumetopias jubatus) were investigated from ‘deceleration during glide’ measurements. A total of 66 glides from six juvenile sea lions yielded a mean drag coefficient (referenced to total wetted surface area) of 0.0056 at a mean Reynolds number of 5.5×106. The drag values indicate that the boundary layer is largely turbulent for Steller sea lions swimming at these Reynolds numbers, which are past the point of expected transition from laminar to turbulent flow. The position of maximum thickness (at 34 % of the body length measured from the tip of the nose) was more anterior than for a ‘laminar’ profile, supporting the idea that there is little laminar flow. The Steller sea lions in our study were characterized by a mean fineness ratio of 5.55. Their streamlined shape helps to delay flow separation, reducing total drag. In addition, turbulent boundary layers are more stable than laminar ones. Thus, separation should occur further back on the animal. Steller sea lions are the largest of the otariids and swam faster than the smaller California sea lions (Zalophus californianus). The mean glide velocity of the individual Steller sea lions ranged from 2.9 to 3.4 m s−1 or 1.2–1.5 body lengths s−1. These length-specific speeds are close to the optimum swim velocity of 1.4 body lengths s−1 based on the minimum cost of transport for California sea lions.
Vertebrate Ancient (Va) Opsin and Extraretinal Photoreception in the Atlantic Salmon (Salmo Salar)
Authors: Philp Alisdair R. , Garcia-Fernandez Jose M. , Soni Bobby G. , Lucas Robert J. , Bellingham James , Foster Russell G.
Published: April 2021

A member of a new photopigment family first isolated from teleost fish, vertebrate ancient (VA) opsin, has recently been shown to form a functional photopigment and to be expressed within a subset of horizontal and amacrine cells of the inner retina. These sites of expression (and structural features) of VA opsin suggest that this photopigment might mediate non-image-forming light-detection tasks. We attempted to gain support for this hypothesis by examining the expression of VA opsin within the central nervous system (CNS) (pineal and deep brain) of the Atlantic salmon Salmo salar. In addition, we examined the sites of rod-opsin, cone-opsin and α-transducin expression within the salmon CNS to provide a more complete description of the extraretinal photoreceptors of a teleost vertebrate. We show that multiple populations of cells within the salmon CNS appear to contain photoreceptors: VA opsin was strongly expressed in the pineal organ and in bilateral columns of subependymal cells in the epithalamus; anti-cone-opsin antibodies labelled cells within the pineal and numerous cells in the anterior hypothalamus (suprachiasmatic nucleus, nucleus preopticus magnocellularis, nucleus preopticus parvocellularis); anti-rod-opsin antibodies labelled cells within the pineal but no other areas within the central brain; and anti-α-transducin antibodies labelled cells within the pineal and the ventral telencephalon. Collectively, our results suggest that VA opsin is a photopigment specialised for irradiance detection tasks within the eye, pineal and central brain, and that the salmon has multiple and varied populations of photoreceptors within the CNS. We review the significance of these findings within the broad context of vertebrate extraretinal photoreception.
Chromaticity as a Signal of Ripeness in Fruits Taken by Primates
Authors: Sumner Petroc , Mollon J. D.
Published: April 2021

We have measured the reflectance spectra of many samples of fruit eaten by chimpanzees and three frugivorous monkey species. If the fruit are plotted in a colour space appropriate for catarrhine primates, several distinct ripening patterns are evident. The degree of ripeness of many species would be discernible by dichromatic primates, but for most fruit a trichromatic consumer would be at an advantage. However, by calculating which set of possible photopigments would maximise the chromatic distance between samples of each fruit species, we show that the spectral positions of the primate long-(L) and middle-wavelength (M) cone pigments are not optimised for this task.
Gaba and Responses to Gaba in the Stomatogastric Ganglion of the Crab Cancer Borealis
Authors: Swensen Andrew M. , Golowasch Jorge , Christie Andrew E. , Coleman Melissa J. , Nusbaum Michael P. , Marder Eve
Published: April 2021

The multifunctional neural circuits in the crustacean stomatogastric ganglion (STG) are influenced by many small-molecule transmitters and neuropeptides that are co-localized in identified projection neurons to the STG. We describe the pattern of γ-aminobutyric acid (GABA) immunoreactivity in the stomatogastric nervous system of the crab Cancer borealis and demonstrate biochemically the presence of authentic GABA in C. borealis. No STG somata show GABA immunoreactivity but, within the stomatogastric nervous system, GABA immunoreactivity co-localizes with several neuropeptides in two identified projection neurons, the modulatory proctolin neuron (MPN) and modulatory commissural neuron 1 (MCN1). To determine which actions of these neurons are evoked by GABA, it is necessary to determine the physiological actions of GABA on STG neurons. We therefore characterized the response of each type of STG neuron to focally applied GABA. All STG neurons responded to GABA. In some neurons, GABA evoked a picrotoxin-sensitive depolarizing, excitatory response with a reversal potential of approximately −40 mV. This response was also activated by muscimol. In many STG neurons, GABA evoked inhibitory responses with both K+- and Cl−-dependent components. Muscimol and β-guanidinopropionic acid weakly activated the inhibitory responses, but many other drugs, including bicuculline and phaclofen, that act on vertebrate GABA receptors were not effective. In summary, GABA is found in projection neurons to the crab STG and can evoke both excitatory and inhibitory actions on STG neurons.
Three-Dimensional Loading and Growth of the Zygomatic Arch
Authors: Rafferty Katherine L. , Herring Susan W. , Artese Flavia
Published: April 2021

Despite a number of previous biomechanical studies on the zygomatic arch, unanswered questions remain about its three-dimensional loading and growth. Using young miniature swine, we have for the first time recorded strains from both the medial and lateral aspects of the squamosal bone during mastication and masseter muscle stimulation. Strains from the zygomatic bone flange and zygomatic arch growth data were also obtained from the same animals. A second study on a younger group of animals examined the growth of the zygomatic flange following partial removal of the masseter. Strain data indicated that the squamosal bone is bent out-of-plane and that this pattern of loading is quite different from that of the adjacent zygomatic bone, which experiences much lower strains with little evidence of out-of-plane bending. Surprisingly, strains were higher in the zygomatic flange during contralateral chews and contralateral masseter stimulations than during ipsilateral chews/stimulations. These strains proved to arise from movement of the condyle, explaining why partial removal of the masseter had little effect on the growth of the flange. Other growth results indicated an approximately threefold greater rate of subperiosteal deposition on the lateral surface of the squamosal bone than on the zygomatic bone. This difference in growth rate is attributed to the presence of sutures that contribute to the lateral displacement of the zygomatic bone but not the squamosal bone. This explanation does not exclude the possibility that the rapid apposition on the lateral squamosal surface is regulated by the high surface strains that result from out-of-plane bending.
Influence of Tail Shape on Tadpole Swimming Performance
Authors: Buskirk Josh Van , Mccollum S. Andy
Published: April 2021

Many tadpoles respond to insect predators by developing deeper, and sometimes longer, tails. It has been assumed that the larger tail enhances aspects of swimming performance, because deep-tailed tadpoles survive well when confronted with hunting predators. We tested this hypothesis using both naturally occurring and surgically created variation in tail morphology of Hyla versicolor tadpoles. We measured swimming performance (maximum speed, time to reach a 2.5 cm radius, and angle of escape) and morphology (size and shape of the body and tail) in 288 tadpoles, of which half possessed the predator-induced morphology and the other half were from predator-free ponds. Large tadpoles swam faster than small ones, and shape was significantly correlated with size-corrected swimming performance. The fastest tadpoles had relatively shallow bodies and tail fins, and short tails; there was no difference in swimming performance between predator-induced and no-predator tadpoles. We performed an experiment to create independent variation in tail depth and length by surgically manipulating tail shape in 270 tadpoles. Three tail-length treatments reduced the length of the tail fin by 21 %, 34 % and 55 %; three tail-depth treatments reduced the maximum depth of the tail fin by 11 %, 34 % and 59 %; two additional treatments controlled for the effects of anaesthesia and surgery. The angle of escape was unaffected by surgery. Maximum speed and minimum escape time were both significantly impaired by the high-removal treatments, but showed no evidence of decline until 30 % of the tail (length or depth) was removed. These results suggest that the relatively deep tails in predator-induced tadpoles (approximately 10 % deeper than in no-predator tadpoles) do not improve performance in burst swimming. Thus, predator-induced tadpoles are less vulnerable to predation for reasons other than enhanced swimming performance.
Drinking in Snakes: Kinematic Cycling and Water Transport
Authors: Cundall David
Published: April 2021

Snakes are purported to drink by sucking water into their mouths and then compressing the oral cavity to force water into the oesophagus. Video recordings of drinking behaviour in 23 snakes representing 14 species from three families, combined with simultaneous recordings of water volumes consumed, show that all the snakes vary widely in the amount of water taken in when drinking. This variation is not correlated with kinematic events. Kinematic recordings and indirect measurements of water flow suggest that moving water into the mouth can be decoupled from the processes that move water into the oesophagus and that, infrequently, water may continue flowing into the mouth during both opening (suction) and closing (presumed compression) of the mouth. Drinking in snakes is not a simple, stereotyped behaviour.

Different snake species differ in both drinking kinematics and water inflow patterns. Vertical excursions of the mandible are smallest in booids and larger, but highly variable, in different viperids and colubrids. Cyclic movements of the tongue seen in booids are not evident in viperids or colubrids. All the snakes usually take in water at rates far below their potential maximum rate.

Although drinking is apparently achieved by suction, a single model cannot explain all water movement patterns in snakes. At a practical level, functional morphological studies of drinking in snakes (and possibly many other animals) must demonstrate that fluid flow actually correlates with kinematic events. Without such an empirical demonstration, interpretation of other measurements (pressure, movement, etc.) is unlikely to produce meaningful models.
Atp Production from the Oxidation of Sulfide in Gill Mitochondria of the Ribbed Mussel Geukensia Demissa
Authors: Parrino Vincent , Kraus David W. , Doeller Jeannette E.
Published: April 2021

The ribbed mussel Geukensia demissa inhabits intertidal Spartina grass marshes characterized by sulfide-rich sediments. Sulfide poisons aerobic respiration, and G. demissa may cope in this seemingly inhospitable environment by oxidizing sulfide in gill mitochondria. Well-coupled mitochondria isolated from G. demissa gills were used to investigate sulfide oxidation and ATP synthesis. State 3 respiration, maximally stimulated by 5 μmol l−1 sulfide with a P/O ratio of 0.89 and a respiratory control ratio (RCR) of 1.40, remained refractory to sulfide at higher concentrations except in the presence of salicylhydroxamic acid (SHAM), an inhibitor of alternative oxidases. Sulfide-stimulated ATP production was 3–5 times greater than that stimulated by malate and succinate, respectively, giving an ATP/sulfide ratio of 0.63. The inhibition of sulfide-stimulated respiration and ATP production by the complex III inhibitors myxothiazol and antimycin A, respectively, suggests that electrons enter the electron transport chain before complex III. Combined with in vivo evidence for electron entry at cytochrome c, these data suggest that more than one type of sulfide-oxidizing enzyme may function in G. demissa gills. The SHAM-sensitive pathway of electron flux may be a critical component of a physiological strategy to tolerate sulfide. We conclude that G. demissa exploits the energy available from its reduced environment by using sulfide as a respiratory substrate for cellular ATP production.
The Effects of Cell Ageing on Protein Synthesis in Rainbow Trout (Oncorhynchus Mykiss) Red Blood Cells
Authors: Lund Susan G. , Phillips Matthew C. L. , Moyes Christopher D. , Tufts Bruce L.
Published: April 2021

The effects of cell age on protein synthesis were examined in the nucleated red blood cells of rainbow trout (Oncorhynchus mykiss). Total DNA content was unaffected by cell age, whereas total RNA content in young red blood cells was roughly ten times as high as that in old red blood cells. The mRNA levels for haemoglobin, carbonic anhydrase and the chloride/bicarbonate (Cl−/HCO3−) exchanger were also approximately tenfold higher in young red blood cells. Although young red blood cells synthesized roughly five times more protein under steady-state conditions, total protein concentration was not affected by cell age. Despite large reductions in mRNA levels with red blood cell ageing, the concentrations and/or activities of the respiratory proteins were largely preserved. In contrast, the ability to mount a heat shock response was greatly reduced in older red blood cells. Young red blood cells produced 13 times more heat shock protein 70 mRNA following heat shock and four times more 70 kDa protein after recovery. They also transcribed much more heat shock cognate 71 and heat shock factor mRNA than did older red blood cells under steady-state conditions.
Nacl Uptake by the Branchial Epithelium in Freshwater Teleost Fish: An Immunological Approach to Ion-Transport Protein Localization
Authors: Wilson Jonathan M. , Laurent Pierre , Tufts Bruce L. , Benos Dale J. , Donowitz Mark , Vogl A. Wayne , Randall David J.
Published: April 2021

Teleost fishes, living in fresh water, engage in active ion uptake to maintain ion homeostasis. Current models for NaCl uptake involve Na+uptake via an apical amiloride-sensitive epithelial Na+channel (ENaC), energized by an apical vacuolar-type proton pump (V-ATPase) or alternatively by an amiloride-sensitive Na+/H+exchange (NHE) protein, and apical Cl−uptake mediated by an electroneutral, SITS-sensitive Cl−/HCO3−anion-exchange protein. Using non-homologous antibodies, we have determined the cellular distributions of these ion-transport proteins to test the predicted models. Na+/K+-ATPase was used as a cellular marker for differentiating branchial epithelium mitochondria-rich (MR) cells from pavement cells. In both the freshwater tilapia (Oreochromis mossambicus) and rainbow trout (Oncorhynchus mykiss), V-ATPase and ENaC-like immunoreactivity co-localized to pavement cells, although apical labelling was also found in MR cells in the trout. In the freshwater tilapia, apical anion-exchanger-like immunoreactivity is found in the MR cells. Thus, a freshwater-type MR chloride cell exists in teleost fishes. The NHE-like immunoreactivity is associated with the accessory cell type and with a small population of pavement cells in tilapia.
Humboldt Penguins Outmanoeuvring El NiñO
Authors: Culik B. , Hennicke J. , Martin T.
Published: April 2021

We satellite-tracked five Humboldt penguins during the strong 1997/98 El Niño Southern Oscillation (ENSO) from their breeding island Pan de Azúcar (26°09′S, 70°40′W) in Northern Chile and related their activities at sea to satellite-derived information on sea surface temperature (SST), sea surface temperature anomaly (SSTA), wind direction and speed, chlorophyll a concentrations and statistical data on fishery landings.

We found that Humboldt penguins migrated by up to 895 km as marine productivity decreased. The total daily dive duration was highly correlated with SSTA, ranging from 3.1 to 12.5 h when the water was at its warmest (+4 °C). Birds travelled between 2 and 116 km every day, travelling further when SSTA was highest. Diving depths (maximum 54 m), however, were not increased with respect to previous years.

Two penguins migrated south and, independently of each other, located an area of high chlorophyll a concentration 150 km off the coast. Humboldt penguins seem to use day length, temperature gradients, wind direction and olfaction to adapt to changing environmental conditions and to find suitable feeding grounds. This makes Humboldt penguins biological in situ detectors of highly productive marine areas, with a potential use in the verification of trends detected by remote sensors on board satellites.
Expression of Arginine Kinase Enzymatic Activity and mRNA in Gills of The Euryhaline Crabs Carcinus Maenas and Callinectes Sapidus
Authors: Kotlyar Simon , Weihrauch Dirk , Paulsen Ryan S. , Towle David W.
Published: April 2021

Phosphagen kinases catalyze the reversible dephosphorylation of guanidino phosphagens such as phosphocreatine and phosphoarginine, contributing to the restoration of adenosine triphosphate concentrations in cells experiencing high and variable demands on their reserves of high-energy phosphates. The major invertebrate phosphagen kinase, arginine kinase, is expressed in the gills of two species of euryhaline crabs, the blue crab Callinectes sapidus and the shore crab Carcinus maenas, in which energy-requiring functions include monovalent ion transport, acid–base balance, nitrogen excretion and gas exchange. The enzymatic activity of arginine kinase approximately doubles in the ion-transporting gills of C. sapidus, a strong osmoregulator, when the crabs are transferred from high to low salinity, but does not change in C. maenas, a more modest osmoregulator. Amplification and sequencing of arginine kinase cDNA from both species, accomplished by reverse transcription of gill mRNA and the polymerase chain reaction, revealed an open reading frame coding for a 357-amino-acid protein. The predicted amino acid sequences showed a minimum of 75 % identity with arginine kinase sequences of other arthropods. Ten of the 11 amino acid residues believed to participate in arginine binding are completely conserved among the arthropod sequences analyzed. An estimation of arginine kinase mRNA abundance indicated that acclimation salinity has no effect on arginine kinase gene transcription. Thus, the observed enhancement of enzyme activity in C. sapidus probably results from altered translation rates or direct activation of pre-existing enzyme protein.
Modulation of the Cost of pHi Regulation During Metabolic Depression: A 31P-NMR Study in Invertebrate (Sipunculus Nudus) Isolated Muscle
Authors: Pörtner H. O. , Bock C. , Reipschläger A.
Published: April 2021

Extracellular acidosis has been demonstrated to play a key role in the process of metabolic depression under long-term environmental stress, exemplified in the marine invertebrate Sipunculus nudus. These findings led to the hypothesis that acid–base regulation is associated with a visible cost depending on the rate and mode of H+-equivalent ion exchange. To test this hypothesis, the effects of different ion-transport inhibitors on the rate of pH recovery during hypercapnia, on energy turnover and on steady-state acid–base variables were studied in isolated body wall musculature of the marine worm Sipunculus nudus under control conditions (pHe 7.90) and during steady-state extracellular acidosis (pHe 7.50 or 7.20) by in vivo31P-NMR and oxygen consumption analyses. During acute hypercapnia (2 % CO2), recovery of pHi was delayed at pHe 7.5 compared with pHe 7.9. Inhibition of the Na+/H+-exchanger by 5-(N,N-dimethyl)-amiloride (DMA) at pHe 7.5 delayed recovery even further. This effect was much smaller at pHe 7.9. Inhibition of anion exchange by the addition of the transport inhibitor 4,4′-diisothiocyanatostilbene-2,2′-disulphonic acid (DIDS) prevented pH recovery at pHe 7.5 and delayed recovery at pHe 7.9, in accordance with an effect on Na+-dependent Cl−/HCO3− exchange. The effects of ouabain, DIDS and DMA on metabolic rate were reduced at low pHe, thereby supporting the conclusion that acidosis caused the ATP demand of Na+/K+-ATPase to fall. This reduction occurred via an inhibiting effect on both Na+/H+- and Na+-dependent Cl−/HCO3− (i.e. Na+/H+/Cl−/HCO3−) exchange in accordance with a reduction in the ATP demand for acid–base regulation during metabolic depression. Considering the ATP stoichiometries of the two exchangers, metabolic depression may be supported by the predominant use of Na+/H+/Cl−/HCO3− exchange under conditions of extracellular acidosis.
The Effect of Alterations in Activity and Body Temperature on the Pulmonary Surfactant System in the Lesser Long-Eared Bat Nyctophilus Geoffroyi
Authors: Slocombe Nicola C. , Codd Jonathan R. , Wood Philip G. , Orgeig Sandra , Daniels Christopher B.
Published: April 2021

Pulmonary surfactant is a mixture of phospholipids, neutral lipids and proteins that controls the surface tension of the fluid lining the lung. It is critical for lung stability and function. The amount and composition of surfactant are influenced by physiological variables such as metabolic rate, body temperature and ventilation. We investigated the plasticity of the pulmonary surfactant system in the microchiropteran bat Nyctophilus geoffroyi throughout a natural 24 h cycle. Bats were housed at 24 °C on a fixed (8 h:16 h) light:dark photoperiod. At 4 h intervals throughout the 24 h period, bats were lavaged and the surfactant analysed for absolute and relative amounts of total phospholipid (PL), disaturated phospholipid (DSP) and cholesterol (Chol). N. geoffroyi experienced two peaks of activity, at 18:00 h and 06:00 h. The amount of surfactant increased 1.5-fold upon arousal from torpor. The proportion of DSP to PL in the surfactant remained constant. Similarly, the Chol/PL and Chol/DSP ratios remained relatively constant. Surfactant cholesterol content did not increase during torpor in N. geoffroyi. Cholesterol does not appear to control surfactant fluidity during torpor in these bats, but instead the cholesterol content exactly mirrored the diurnal changes in body temperature.
Ventilatory and Cardiovascular Responses of a Python (Python Molurus) To Exercise and Digestion
Authors: Secor Stephen M. , Hicks James W. , Bennett Albert F.
Published: April 2021

To investigate the potential limiting steps of peak metabolic rates, we examined gas exchange rates , respiratory exchange ratio (RER), breathing frequency, tidal volume, minute ventilation volume as well as the heart rate, systemic blood flow and stroke volume of Burmese pythons (Python molurus) while fasting at rest, exercising, digesting and exercising while digesting. All measured variables increased significantly during exercise (crawling at 0.4 km h−1 and at ), highlighted by a 17-fold increase in and a 24-fold increase in .

During the digestion of a meal equivalent to 25 % of the snake’s body mass, pythons responded with increases in and heart rate similar to those experienced during exercise, along with a 4.5-fold increase in systemic blood flow. Interestingly, pythons hyperventilated while exercising, whereas they hypoventilated during digestion. The combined demands of exercise and digestion resulted in significantly higher breathing frequency and heart rate than during either exercise or digestion alone. Evidently, the capacities of the ventilatory and cardiovascular systems to transport oxygen to locomotor muscles are not a limiting factor in the attainment of peak metabolic rates during exercise in pythons
Early Specialization of the Superfast Myosin in Extraocular and Laryngeal Muscles
Authors: Briggs Margaret M. , Schachat Fred
Published: April 2021

Extraocular muscle (EOM) exhibits high-velocity, low-tension contractions compared with other vertebrate striated muscles. These distinctive properties have been associated with a novel myosin heavy chain (MyHC) isoform, MyHC-EO. An atypical MyHC, MyHC IIL, has also been identified in laryngeal muscles that have similarly fast contractile properties. It co-migrates with MyHC-EO on high-resolution SDS gels, but appeared to be encoded by a different mRNA. We combined CNBr peptide maps and full-length cDNA sequences to show that rabbit muscle EO and IIL MyHCs are identical. Analysis of the 5′ untranslated region (5′UTR) of the mRNAs identified three variants that result from a combination of alternative splicing and multiple transcription initiation sites. This complex pattern of 5′UTRs has not been reported previously for MyHC genes. We identified the human homologue of the MyHC-EO gene in GenBank, and analyzed the 5′ upstream region, which revealed a paucity of muscle-specific transcription factor binding sites compared with the other MyHC genes. These features are likely to be critical to the unique regulation and tissue-specific expression of the MyHC-EO/IIL gene.

Phylogenetic analysis indicates that MyHC-EO/IIL diverged from an ancestral MyHC gene to generate the first specialized fast myosin. The catalytic S1 head domain is more closely related to the fast MyHCs, while the rod is more closely related to the slow/cardiac MyHCs. The exon boundaries of the MyHC-EO are identical to those of the embryonic MyHC gene and virtually identical to those of the α and β cardiac genes. This implies that most of the current exon boundaries were present in the ancestral gene, predating the duplications that generated the family of skeletal and cardiac myosin genes.
Evidence of a Guanylyl Cyclase Natriuretic Peptide Receptor in the Gills Of the New Zealand Hagfish Eptatretus Cirrhatus (Class Agnatha)
Authors: Callahan Will , Forster Malcolm , Toop Tes
Published: April 2021

Natriuretic peptide binding sites were examined in the gills of the hagfish Eptatretus cirrhatus (Class Agnatha, subfamily Eptatretinae) using radio-ligand binding techniques, molecular cloning and guanylyl cyclase assays. Iodinated rat atrial natriuretic peptide (125 I-rANP) and iodinated porcine C-type natriuretic peptide (125 I-pCNP) bound specifically to the lamellar folds and cavernous tissue of E. cirrhatus gills, and 0.3 nmol l−1 rat ANP competed for 50 % of specific 125 I-rANP binding sites. Affinity cross-linking of 125 I-rANP to gill membranes followed by sodium dodecylsulphate–polyacrylamide gel electrophoresis revealed a single binding site of 150 kDa. In the presence of Mn2+, 0.1 nmol l−1 rANP inhibited cGMP production, whereas 1 μmol l−1 rANP stimulated cGMP production rates. At 1 μmol l−1, pCNP also stimulated cGMP production. The production of cGMP was also measured in the presence and absence of ATP with either Mn2+ or Mg2+.

Reverse transcriptase polymerase chain reaction (RT-PCR) of hagfish gill RNA, followed by cloning and sequencing of PCR products, produced a partial cDNA sequence of a natriuretic peptide guanylyl cyclase receptor. The deduced amino acid sequence indicated 87–91 % homology with other natriuretic peptide guanylyl cyclase receptors. This study indicates the presence of a natriuretic peptide guanylyl cyclase receptor in the gills of E. cirrhatus that is similar to the natriuretic peptide guanylyl cyclase receptors in higher vertebrates. These observations demonstrate that the coupling of natriuretic peptide receptors with guanylyl cyclase has a long evolutionary history.
Early Thermal Experience has Different Effects on Growth and Muscle Fibre Recruitment in Spring- and Autumn-Running Atlantic Salmon Populations
Authors: Johnston Ian A. , Mclay H. Anne , Abercromby Marguerite , Robins Duncan
Published: April 2021

The consequence of early thermal experience for subsequent growth patterns was investigated in Atlantic salmon (Salmo salar L.). Spring- and autumn-running salmon were caught in upland (Baddoch) and lowland (Sheeoch) tributaries of the River Dee, Aberdeenshire, Scotland, respectively, on the final stages of their spawning migrations. The eggs were incubated at the simulated natural temperature regime of each stream, which was on average 2.8 °C lower for the Baddoch. The offspring, representing 11 families per population, were transferred at first feeding to constant environmental conditions (12–14 °C; 16 h:8 h light:dark photoperiod) and reared in replicate tanks. Salmon of both populations were longer and heavier at 6 and 12 weeks in fish initially reared under the cooler Baddoch regime. Length frequency distributions became bimodal after 18 weeks, and only the upper growth mode was studied. Modelling of length distributions at 40 weeks revealed significantly different patterns of muscle growth according to initial temperature regime, but only for the Sheeoch salmon. In fish of Sheeoch origin, significantly more white muscle fibres were recruited per mm2 increase in myotomal cross-sectional area at Sheeoch than at Baddoch temperatures (P<0.01). After 40 weeks, the density of white fibres was 10.4 % higher in fish initially reared at the Sheeoch (533±6 mm−2 ) than at the Baddoch (483±5 mm−2 ) thermal regimes (means ± S.E.M., 16 fish per group; P<0.001). Muscle satellite cells were identified using an antibody to c-met. At 24 weeks, the density of muscle satellite cells was 29 % higher in Sheeoch salmon reared to first feeding at the temperature of their natal stream than at cooler Baddoch temperatures (P<0.01). In contrast, the number and size distributions of white muscle fibres in the myotomes of Baddoch salmon were independent of early thermal experience.
Limits to Optimization: Fluid Dynamics, Adhesive Strength and the Evolution of Shape in Limpet Shells
Authors: Denny Mark W.
Published: April 2021

Limpets are commonly found on wave-swept rocky shores, where they may be subjected to water velocities in excess of 20 m s−. These extreme flows can impose large forces (lift and drag), challenging the animal’s ability to adhere to the substratum. It is commonly thought that the conical shape of limpet shells has evolved in part to reduce these hydrodynamic forces while providing a large aperture for adhesion. This study documents how lift and drag actually vary with the shape of limpet-like models and uses these data to explore the potential of hydrodynamic forces to serve as a selective factor in the evolution of limpet shell morphology. At a low ratio of shell height to shell radius, lift is the dominant force, while at high ratios of height to radius drag is dominant. The risk of dislodgment is minimized when the ratio of height to radius is 1.06 and the apex is in the center of the shell. Real limpets are seldom optimally shaped, however, with a typical height-to-radius ratio of 0.68 and an apex well anterior of the shell’s center. The disparity between the actual and the hydrodynamically optimal shape of shells may be due to the high tenacity of limpets’ adhesive system. Most limpets adhere to the substratum so strongly that they are unlikely to be dislodged by lift or drag regardless of the shape of their shell. The evolution of a tenacious adhesion system (perhaps in response to predation) has thus pre-empted selection for a hydrodynamically optimal shell, allowing the shell to respond to alternative selective factors.