bluuebunny/crossref_metadata_2025 huggingface dataset:
An Electrophysiological Survey of Frog Olfactory Cilia
Authors: Kleene Steven J. , Gesteland Robert C. , Bryant Shirley H.
Published: April 2021

Individual olfactory receptor neurons vary widely in their responses to odorants. Olfactory stimulus reception occurs in the cilia of the receptor neurons. Thus, the variability among individual neurons could in part be due to differences among the olfactory cilia. We have quantified the known conductance properties of each of 117 frog olfactory cilia. From a strictly qualitative viewpoint, the cilia were very homogeneous. All but a few of them had a basal conductance in the absence of odorants and second messengers, conductances stimulated by cytoplasmic cyclic AMP and by Ca2+ and a conductance measured in the presence of ATP and stimulated by GTPγS. However, the magnitudes of the conductances varied widely among the cilia. Amplitudes of the cyclic-AMP-and Ca2+-activated ciliary currents correlated strongly with one another across the 117 cilia and 24 frogs studied, suggesting that expression of the underlying channels may be co-regulated. None of the conductance properties correlated strongly with ciliary length, a marker of cell maturity. Given cytoplasmic MgATP as substrate, ciliary adenylate cyclase apparently produced cyclic AMP, which in turn gated membrane channels and increased the ciliary conductance. In some cilia, MgATP alone caused a very large increase in conductance. In others, there was little effect unless GTPγS, which increases cyclase activity, was also added. No effect of cytoplasmic inositol trisphosphate on ciliary conductance was detectable.
Extracellular and Intracellular Carbon Dioxide Concentration as a Function of Temperature in the Toad Bufo Marinus
Authors: Stinner J. N. , Newlon D. L. , Heisler N.
Published: April 2021

Previous studies of reptiles and amphibians have shown that changing the body temperature consistently produces transient changes in the respiratory exchange ratio (RE) and, hence, changes in whole-body CO2 stores, and that the extracellular fluid compartment contributes to the temperature-related changes in CO2 stores. The purpose of this study was to determine whether the intracellular fluid compartment contributes to the changes in CO2 stores in undisturbed resting cane toads. Increasing body temperature from 10 to 30°C temporarily elevated RE, and returning body temperature to 10°C temporarily lowered RE. The estimated average change in whole-body CO2 stores associated with the transient changes in RE was 1.0±0.8 mmol kg−1 (±S.D., N=6). Plasma [CO2] and, thus, extracellular fluid [CO2], were unaffected by the temperature change. Plasma calcium levels were also unaffected, so that bone CO2 stores did not contribute to changes in whole-body CO2 stores. Intracellular [CO2] was determined for the lung, oesophagus, stomach, small intestine, liver, ventricle, red blood cells, skin and 14 skeletal muscles. [CO2] was significantly lower (P<0.05) at higher temperature in 10 of these, and seven others, although not statistically significant (P>0.05), had mean values at least 0.5 mmol kg−1 lower at the higher temperature. The average change in intracellular [CO2] for all tissues examined was -0.165 mmol kg−1°C−1. We conclude that, in cane toads, the temperature-related transients in RE result from intracellular CO2 adjustments, that different tissues have unique intracellular CO2/temperature relationships, and that a combination of respiratory and ion-exchange mechanisms is used to adjust pH as temperature changes.
Motion-Sensitive Cells: Putative Larval Neurones Incorporated Into the Optic Lobe of the Adult Swallowtail Butterfly
Authors: Ichikawa Toshio
Published: April 2021

Intracellular recordings were made from neurones with large somata situated at the anteromedial edge of the medulla of the swallowtail butterfly Papilio xuthus; the neurones were then filled with Lucifer Yellow. These cells are putative larval visual interneurones incorporated into the adult optic lobe of the butterfly. There are four classes of motion-sensitive neurones. Two have a dendritic arborization in the dorsal half of the medulla and project an axon to the medial protocerebrum or the contralateral medulla. They respond to vertical downward motion with a strong burst of action potentials and their background activities are inhibited by motion in the opposite direction. Variations in position of the dendritic fields suggest that each group of neurones forms a coherent set of cells detecting vertical motion in the dorsal half of the visual field of the eye. The third class of neurones connects the lobula plate to the midbrain and is preferentially sensitive to vertical upward motion. The fourth class of neurones has a dendritic arborization in the lobula. These neurones are tonically excited by a moving grating irrespective of the stimulus orientation and movement direction. The presence of motion-sensitive medulla neurones suggests that the detection of local motion is completed in the distal medulla.
y+-type cationic amino acid transport: expression and regulation of the mCAT genes
Authors: MacLeod Carol L. , Finley Kim D. , Kakuda Donald K.
Published: April 2021

The transport of cationic amino acids across animal cell membranes is largely mediated by a small group of well-described transport systems (y+, bo,+, Bo,+). Only recently have genes encoding transport proteins in some of these systems been isolated. Two genes, mCAT-1 and mCAT-2, encode related multiple membrane-spanning proteins that share substantial amino acid sequence identity and virtually superimposable hydrophilicity profiles. mCAT-1 and mCAT-2 proteins expressed in Xenopus oocytes are functionally indistinguishable and similar to transport system y+, but have distinct tissue distribution patterns. mCAT-1 expression is nearly ubiquitious and produces a single protein, while mCAT-2 is highly tissue-specific, has two distinct protein isoforms encoded by a single gene and is expressed in different tissues using at least two widely separated promotors. All three proteins facilitate the ion-independent transport of arginine, lysine and ornithine. Both mCAT-1 and mCAT-2 proteins have low amino acid sequence similarity but strikingly similar hydrophilicity profiles with amino acid antiporters, uniporters and symporters of yeast, fungi and eubacteria. Current work will elucidate whether any of the mCAT proteins interact with members of a newly identified family of single membrane-spanning proteins, such as rBAT, 4F2 and NAA-Tr, which are thought to modulate or activate y+L and/or bo,+ transport systems.
Structure, Function and Evolution of Solute Transporters in Prokaryotes and Eukaryotes
Authors: Hediger Matthias A.
Published: April 2021

In both prokaryotes and eukaryotes, transport systems of organic solutes can be classified as passive transporters, such as channels and facilitated transporters, and active transporters, which utilize diverse energy-coupling mechanisms. In the past decade, our understanding of the biochemistry and molecular biology of transporters from Escherichia coli has progressed significantly, whereas the analysis of mammalian transporters has initially been limited by the ability to purify membrane proteins. The recent development of methods to detect the activity of recombinant proteins in individual cells, however, has led to the cloning of several novel mammalian transporter cDNAs. One of the most useful expression cloning systems is Xenopus oocytes in conjunction with uptake studies and electrophysiological experiments. Overall, the sequence information and the functional data derived from many transporters has revealed unifying designs, similar energy-coupling mechanisms and common evolutionary origins. Here, I will provide a general survey of the known transport systems in bacteria, yeast, plants, insects and vertebrates and illustrate the different types of transport systems in mammals by discussing transporters recently studied in our laboratory.
‘Active’ Sugar Transport In Eukaryotes
Authors: Wright Cernest M. , Loo Donald D. F. , Panayotova-Heiermann Mariana , Lostao M. Pilar , Hirayama Bruce H. , Mackenzie Bryan , Boorer Kathyrn , Zampighi Guido
Published: April 2021

Sugar transporters in prokaryotes and eukaryotes belong to a large family of membrane proteins containing 12 transmembrane alpha-helices. They are divided into two classes: one facilitative (uniporters) and the other concentrative (cotransporters or symporters). The concentrative transporters are energised by either H+ or Na+ gradients, which are generated and maintained by ion pumps. The facilitative and H+-driven sugar transporters belong to a gene family with a distinctive secondary structure profile. The Na+-driven transporters belong to a separate, small gene family with no homology at either the primary or secondary structural levels. It is likely that the Na+-and H+-driven sugar cotransporters share common transport mechanisms. To explore these mechanisms, we have expressed cloned eukaryote Na+/sugar cotransporters (SGLT) in Xenopus laevis oocytes and measured the kinetics of sugar transport using two-electrode voltage-clamp techniques. For SGLT1, we have developed a six-state ordered model that accounts for the experimental data. To test the model we have carried out the following experiments. (i) We measured pre-steady-state kinetics of SGLT1 using voltage-jump techniques. In the absence of sugar, SGLT1 exhibits transient carrier currents that reflect voltage-dependent conformational changes of the protein. Time constants for the carrier currents give estimates of rate constants for the conformational changes, and the charge movements, integrals of the transient currents, give estimates of the number and valence of SGLT1 proteins in the plasma membrane. Ultrastructural studies have confirmed these estimates of SGLT1 density. (ii) We have perturbed the kinetics of the cotransporter by site-directed mutagenesis of selected residues. For example, we have identified a charged residue which dramatically changes the kinetics of charge transfer. (iii) We have examined the kinetics of sugar and Na+ analogs. The Vmax of sugar transport decreases dramatically with bulky phenyl glucosides and increases when H+ replaces Na+. These results permit us to extend and refine our model for transport. The model has been useful in the analysis of mutant SGLT1 proteins: in the case of a D176A mutant, the primary effect is to alter rates of conformational changes of the unloaded protein, and with the glucose/galactose malabsorption syndrome mutant D28N SGLT1, the mutation disrupts the delivery of SGLT1 glycosylated protein from the endoplasmic reticulum to the plasma membrane.
Functional significance of the beta-subunit for heterodimeric P-type ATPases
Authors: Chow Dar C. , Forte John G.
Published: April 2021

We have reviewed the structural and functional role of the β-subunit in a subfamily of the P-ATPases known as the α/ β-heterodimeric, cation-exchange ATPases. The subfamily consists of the various isoforms of Na+/K+-ATPase and H+/K+-ATPase, both of which pump a cation out of the cell (Na+ or H+, respectively) in recycle exchange for K+. Much of the earlier work has emphasized the functional activities of the α-subunit, which shares many characteristics with the broader P-ATPase family. It is now clear that the glycosylated β-subunit is an essential component of the cation-exchange ATPase subfamily. All β-subunit isoforms have three highly conserved disulfide bonds within the extracellular domain that serve to stabilize the α-subunit, α/ β interaction and functional activity of the holoenzyme. Evidence strongly suggests that the β-subunit is involved in the K+-dependent reactions of the enzymes, such as the E1-E2 transition and K+ occlusion, and that the extracellular domain of the β-subunit plays an important role in determining the kinetics of K+ interaction. In most vertebrate cells, the unassociated α-subunit is restricted to the endoplasmic reticulum (ER), and assembly of the complex occurs within the ER. Signals for exiting the ER and directing the correct intracellular trafficking are primarily determined by the β-subunit; Na+/K+-ATPase typically terminates in the plasma membrane facing the basolateral membrane, whereas all isoforms of H+/K+-ATPase terminate in the apical membrane. The C-terminal extracellular domain of the β-subunit is important for proper interaction with the α-subunit and for correct intracellular trafficking. Oligosaccharides on the β-subunit are not essential for enzyme function, but do serve to enhance the efficiency of α/ β association by increasing the lifetime of the unassociated β-subunit and the stability of the α/ β complex to tryptic attack. We propose that highly specialized glycosylation on the β-subunit of the gastric H+/K+-ATPase may help to protect that enzyme from the harsh extracellular environment of the stomach.
Evidence for Hydrodynamic Orientation by Spiny Lobsters in a Patch Reef Environment
Authors: Nevitt Gabrielle A. , Pentcheff N. Dean , Lohmann Kenneth J. , Zimmer-Faust Richard K.
Published: April 2021

Western Atlantic spiny lobsters (Panulirus argus) are superb underwater navigators. Spiny lobsters perform dramatic seasonal offshore migrations and have also been shown to locate and home to specific den sites within the elaborate coral reef environment in which they live. How these animals perform such complex orientation tasks is not known. The study reported here was designed to explore the sensory mechanisms that spiny lobsters use to orient in and around a familiar patch reef environment. Our results show that, in the absence of visual cues, lobsters displaced a short (50 m) distance off the reef do not initially (i.e. within 20 min) travel towards their dens or return to the patch reef where their dens are located. Instead, the headings lobsters follow are significantly correlated to the direction of local hydrodynamic cues and, specifically, to the direction of approaching wave surge. Results from ultrasonic tracking experiments over longer periods (24 h) suggest that displaced lobsters are able to relocate the reef where they were captured, even without visual cues. These results suggest that hydrodynamic cues may provide useful and immediate directional information to lobsters within the local environment of the home reef.
Sodium-Dependent Norepinephrine-Induced Currents in Norepinephrine-Transporter-Transfected Hek-293 Cells Blocked by Cocaine and Antidepressants
Authors: Galli Aurelio , Defelice Louis J. , Duke Billie-Jeanne , Moore Kimberly R. , Blakely Randy D.
Published: April 2021

Transport of norepinephrine (NE+) by cocaine- and antidepressant-sensitive transporters in presynaptic terminals is predicted to involve the cotransport of Na+ and Cl-, resulting in a net movement of charge per transport cycle. To explore the relationship between catecholamine transport and ion permeation through the NE transporter, we established a human norepinephrine transporter (hNET) cell line suitable for biochemical analysis and patch-clamp recording. Stable transfection of hNET cDNA into HEK-293 (human embryonic kidney) cells results in lines exhibiting (1) a high number of transporter copies per cell (106), as detected by radioligand binding and hNET-specific antibodies, (2) high-affinity, Na+-dependent transport of NE, and (3) inhibitor sensitivities similar to those of native membranes. Whole-cell voltage-clamp of hNET-293 cells reveals NE-induced, Na+-dependent currents blocked by antidepressants and cocaine that are absent in parental cells. In addition to NE-dependent currents, transfected cells possess an NE-independent mode of charge movement mediated by hNET. Hnet antagonists without effect in non-transfected cells abolish both NE-dependent and NE-independent modes of charge movement in transfected cells. The magnitude of NE-dependent currents in these cells exceeds the expectations of simple carrier models using previous estimates of transport rates. To explain our observations, we propose that hNETs function as ion-gated ligand channels with an indefinite stoichiometry relating ion flux to NE transport. In this view, external Na+ and NE bind to the transporter with finite affinities in a cooperative fashion. However, coupled transport may not predict the magnitude or the kinetics of the total current through the transporter. We propose instead that Na+ gates NE transport and also the parallel inward flux of an indeterminate number of ions through a channel-like pore.
The Development of Thermotolerance Protects Blowfly Flight Muscle Mitochondrial Function From Heat Damage
Authors: El-Wadawi Rukaya , Bowler Ken
Published: April 2021

The LD50 of 10-day-old adult blowflies was determined to be 38.12±0.07 ˚C.

A transitory increase in heat resistance occurred following the exposure of adult blowflies to a sublethal heat shock at 36 ˚C. This thermotolerance was apparent 1 h after the application of the shock, was maximal 2–3 h later and had disappeared 6 h after exposure.

Oxidative phosphorylation by flight muscle mitochondria from control flies was impaired by an LD50 dose in vivo using both pyruvate+proline (P+P) and glycerol 3-phosphate (G3P) as substrates. Acceptor control (state III respiration/state IV respiration) was lost with G3P as substrate and so ADP:O ratios were not measurable.

The effect of experimental temperature in vitro on respiratory performance of mitochondria isolated from control and thermotolerant flies was also determined between 19 and 39 ˚C. State III respiration was markedly temperature-dependent in mitochondria from control flies with both substrates; it was maximal at 24–29 ˚C and fell progressively at higher measuring temperatures. In mitochondria from thermotolerant flies, state III respiration was less temperature-dependent with both substrates but this was most marked for G3P. The effect of experimental temperature on state IV respiration was similar in mitochondria from control and thermotolerant flies with each substrate, but differed between the two substrates. With G3P as substrate, respiration rate rose with temperature with a Q10 of approximately 1.5; however, with P+P as substrate, the trend was for respiration rate to fall as experimental temperature rose.

Using G3P as substrate, acceptor control was demonstrable at 34 ˚C in some preparations of mitochondria from thermotolerant flies but not in those from control flies at that temperature. With P+P as substrates, acceptor control was demonstrable in mitochondria from both control and thermotolerant flies at all experimental temperatures.
Distribution and action of SALMFamide neuropeptides in the starfish Asterias rubens
Authors: Elphick Maurice R. , Newman Suzanna J. , Thorndyke Michael C.
Published: April 2021

The SALMFamides S1 and S2 are two structurally related neuropeptides that are present in starfish, and which share the C-terminal amino acid sequence SXLXFamide, where X is variable. To establish the distribution of S1 and S2 in starfish, we have raised antisera that recognise specifically the C-terminal pentapeptide sequence of either S1 or S2. Here we describe the production and characterisation of an S2-specific antiserum designated CLII. This antiserum, together with an S1-specific antiserum (BLII), has been used in a radioimmunoassay to measure S1 and S2 levels in extracts of body parts from the starfish Asterias rubens. High concentrations (250–400 pmol g-1) of both peptides were detected in the radial nerve cords of the nervous system and lower concentrations were detected in other body parts, including neuromuscular organs such as the tube feet, apical muscle and cardiac stomach. We have examined the pharmacological effects of S1 and S2 on the contractility of these three preparations. Neither S1 nor S2 influenced the tone of tube foot and apical muscle preparations but S2 caused relaxation of cardiac stomach preparations, antagonising the contracting action of acetylcholine.
Initiation of locomotion by lateral line photoreceptors in lamprey: behavioural and neurophysiological studies
Authors: Deliagina T. G. , Ullén F. , Gonzalez M.-J. , Ehrsson H. , Orlovsky G. N. , Grillner S.
Published: April 2021

The lateral line system of lampreys includes photoreceptors distributed in the skin of the tail region. These are innervated by the trunk lateral line nerves, and the afferents terminate bilaterally in the medial octavolateral nucleus, crossing the midline through the cerebellar commissure. Stimulation of the dermal photoreceptors by tail illumination initiates locomotion. The present study was performed to characterize the response to illumination in larval and adult lampreys in detail and to elucidate the neuronal pathways responsible for the activation of locomotion. In both larval and adult quiescent lampreys, the response to unilateral illumination of the tail was found to consist of an initial turn followed by rectilinear swimming. The sign and magnitude of the turning angle were not correlated with the laterality of the optic stimulus. In mechanically restrained lampreys, spinalized at the level of segments 15–20, tail illumination evoked a complex motor response in the rostral part of the body, with switches between different patterns of coordination (turns in different directions, locomotion, and turns combined with locomotion). Thus, the response to tail illumination is not a simple reflex, but includes a behavioural choice.

Reticulospinal neurones play a crucial role in the initiation of locomotion in lampreys. The response to unilateral tail illumination in rhombencephalic reticular cells was studied with extracellular single-unit recordings. It was found that neurones in the middle and posterior rhombencephalic reticular nuclei were activated bilaterally. Tonic activity or slow bursts (<0.5 Hz) were evoked, in some cases lasting up to 60 s after the stimulation. The response remained bilateral after transection of one lateral line nerve and the cerebellar commissure. Afferents from one side can thus activate reticulospinal cells on both sides through a pathway outside the cerebellar commissure. This bilateral activation of reticulospinal neurones is presumably responsible for the activation of spinal locomotor networks, without any directional bias to the left or the right side, and for the rectilinear swimming observed in behavioural experiments.

In the caudal part of the termination area of the lateral line nerve afferents, neurones with contralateral projections were retrogradely stained with horseradish peroxidase. These neurones appear to be likely candidates for mediating the contralateral effects of the lateral line fibres.
The Force–velocity Relationship of the Atp-Dependent Actin–Myosin Sliding Causing Cytoplasmic Streaming in Algal Cells, Studied Using a Centrifuge Microscope
Authors: Chaen S. , Inoue J. , Sugi H.
Published: April 2021

When uncoated polystyrene beads suspended in Mg-ATP solution were introduced into the internodal cell of an alga Chara corallina, the beads moved along the actin cables with directions and velocities (30–62 µm s−1) similar to those of native cytoplasmic streaming. Bead movement was inhibited both in the absence of ATP and in the presence of Ca2+, as with native cytoplasmic streaming. These results indicate that bead movement is caused by cytoplasmic myosin molecules attached to the bead surface interacting with actin cables. The steady-state force–velocity relationship of the actin–myosin sliding that produces cytoplasmic streaming was determined by applying constant centrifugal forces to the beads moving on the actin cables. The force–velocity curve in the positive load region was nearly straight, and the implications of this shape are discussed in connection with the kinetic properties of the actin–myosin interaction in cytoplasmic streaming. It is suggested that the time for which a cytoplasmic myosin head is detached from actin in one cycle of actin–myosin interaction is very short. The Ca2+-induced actin–myosin linkages, responsible for the Ca2+-induced stoppage of cytoplasmic streaming, were shown to be much stronger than the rigor actin–myosin linkages.
The Role of l-Dopa in the Nervous System of Sea Anemones: A Putative Inhibitory Transmitter in Tentacles
Authors: Hudman Diane , McFARLANE Ian D.
Published: April 2021

L-Dopa evokes transitory inhibition of spontaneous contractions of tentacle longitudinal muscles in sea anemones. It also modulates spontaneous contractions of the sphincter muscle in isolated preparations and whole animals. Extracellular recordings from the tentacles of Calliactis parasitica show that L-Dopa evokes bursts of electrical events apparently associated with a local nerve net. We propose that L-Dopa be added to the growing list of putative transmitter substances in sea anemones, its action being to coordinate local inhibition of spontaneous tentacle contractions.
Serotonergic Modulation of Swimming Speed in the Pteropod Mollusc Clione Limacina: III. Cerebral Neurons
Authors: Satterlie Richard A. , Norekian Tigran P.
Published: April 2021

Swim acceleration in Clione limacina can occur via central inputs to pattern generator interneurons and motor neurons and through peripheral inputs to the swim musculature. In the previous paper, peripheral modulation of the swim muscles was shown to increase wing contractility. In the present paper, central inputs are described that trigger an increase in swim frequency and an increase in motor neuron activity. In dissected preparations, spontaneous acceleration from slow to fast swimming included an increase in the cycle frequency, a baseline depolarization in the swim interneurons and an increase in the intensity of motoneuron firing. Similar effects could be elicited by bath application of 10−5 mol l−1 serotonin. Two clusters of cerebral serotonin-immunoreactive interneurons were found to produce acceleration of swimming accompanied by changes in neuronal activity. Posterior cluster neurons triggered an increase in swim frequency, depolarization of the swim interneurons, an increase in general excitor motoneuron activity and activation of type 12 interneurons and pedal peripheral modulatory neurons. Cells from the anterior cerebral cluster also increased swim frequency, increased activity in the swim motoneurons and activated type 12 interneurons, pedal peripheral modulatory neurons and the heart excitor neuron. The time course of action of the anterior cluster neurons did not greatly outlast the duration of spike activity, while that of the posterior cluster neurons typically outlasted burst duration. It appears that the two discrete clusters of serotonin-immunoreactive neurons have similar, but not identical, effects on swim neurons, raising the possibility that the two serotonergic cell groups modulate the same target cells through different cellular mechanisms.
Functional Characterization of Leucine Transport Induced in Xenopus Laevis Oocytes Injected With mRNA Isolated From Midguts of Lepidopteran Larvae (Philosamia Cynthia)
Authors: Sacchi V. Franca , Perego Carla , Magagnin Simona
Published: April 2021

The injection of poly(A)+ mRNA prepared from Philosamia cynthia midgut caused time-and dose-dependent increases of leucine transport in Xenopus laevis oocytes, with an increase in leucine uptake 1.5–3 times that of oocytes injected with water. When the NaCl concentration was reduced from 100 to 5 mmol l−1, the difference between mRNA-and water-injected oocytes was greater and a fourfold increase of L-leucine uptake was measured. D-Leucine (10 mmol l−1) completely inhibited the induced uptake of 0.1 mmol l−1 L-leucine. The newly expressed component of L-leucine uptake increased at alkaline pH and was abolished by incubation for 15 min with 15 mmol l−1 phenylglyoxal. The mean Km values, calculated using Na+ activation curves of leucine uptake, were 23.3±6.1 mmol l−1 in water-injected oocytes and 0.4±0.2 mmol l−1 for the newly expressed component of leucine uptake in mRNA-injected oocytes. On the basis of these results, we conclude that the increase of L-leucine uptake in mRNA-injected oocytes was due to the expression of a new transport system, which differs from the endogenous ones and shares many features with that found previously in Philosamia cynthia midgut.
The Emg–Force Relationship of the Cat Soleus Muscle and its Association with Contractile Conditions During Locomotion
Authors: Guimaraes A. C. , Herzog W. , Allinger T. L. , Zhang Y. T.
Published: April 2021

The relationship between force and electromyographic (EMG) signals of the cat soleus muscle was obtained for three animals during locomotion at five different speeds (154 steps), using implanted EMG electrodes and a force transducer. Experimentally obtained force–IEMG (=integrated EMG) relationships were compared with theoretically predicted instantaneous activation levels calculated by dividing the measured force by the predicted maximal force that the muscle could possibly generate as a function of its instantaneous contractile conditions. In addition, muscular forces were estimated from the corresponding EMG records exclusively using an adaptive filtering approach. Mean force–IEMG relationships were highly non-linear but similar in shape for different cats and different speeds of locomotion. The theoretically predicted activation–time plots typically showed two peaks, as did the IEMG–time plots. The first IEMG peak tended to be higher than the second one and it appeared to be associated with the initial priming of the muscle for force production at paw contact and the peak force observed early during the stance phase. The second IEMG peak appeared to be a burst of high muscle activation, which might have compensated for the levels of muscle length and shortening velocity that were suboptimal during the latter part of the stance phase. Although it was difficult to explain the soleus forces on the basis of the theoretically predicted instantaneous activation levels, it was straightforward to approximate these forces accurately from EMG data using an adaptive filtering approach.
Ca2+ and Zn2+ Are Transported by the Electrogenic 2Na+/1H+ Antiporter in Echinoderm Gastrointestinal Epithelium
Authors: Zhuang Zhenpeng , Duerr Jeffrey M. , Ahearn Gregory A.
Published: April 2021

45Ca2+ uptake by purified brush-border membrane vesicles of starfish (Pycnopodia helianthoides) pyloric ceca was stimulated by an outwardly directed H+ gradient and this stimulation was enhanced by the simultaneous presence of an induced membrane potential (inside negative; K+/valinomycin). External amiloride (competitive inhibitor; Ki=660 μmol l−1) and a monoclonal antibody raised against proteins associated with the lobster (Homarus americanus) electrogenic 2Na+/1H+ antiporter both inhibited approximately half of the proton-gradient-stimulated 45Ca2+ uptake. These results suggested that Ca2+ might be transported by the electrogenic antiporter and that the crustacean antibody was inhibitory to the exchange function in echinoderms, as was recently shown in crustacean epithelial brush-border membrane vesicles. Carrier-mediated 45Ca2+ influx by amiloride-sensitive and amiloride-insensitive systems displayed the following kinetic constants: (amiloride-sensitive) Kt=66±2 μmol l−1; Jmax=0.173±0.002 pmol μg−1 protein 8 s−1; (amiloride-insensitive) Kt=18±0.3 μmol l−1; Jmax=0.100±0.001 pmol μg−1 protein 8 s−1. Zn2+ was a mixed inhibitor of 45Ca2+ influx by carrier-mediated transport, displaying a Ki of 920 μmol l−1. Mn2+, Cu2+, Fe2+ and Mg2+ also inhibited 45Ca2+ uptake, but the mechanism(s) of inhibition by these other cations was not disclosed. An equilibrium shift experiment showed that both Na+ and Zn2+ were able to exchange with equilibrated 45Ca2+ in these vesicles, suggesting that both monovalent and divalent cations were able to enter pyloric cecal cells through a common carrier-mediated transport system. In addition, the echinoderm electrogenic system appeared to exhibit a molecular component recognized by the crustacean antibody that may imply a similar epitope in the two animals.
On The Mechanism of Isomerization of Ocular Retinoids by the Crayfish Procambarus Clarkii
Authors: Srivastava Ranjana , Goldsmith Timothy H.
Published: April 2021

The eyes of some crustaceans store substantial amounts of retinyl esters, with most of the retinol in the 11-cis configuration. Earlier work in this laboratory suggested that in lobster and crayfish the mechanism of isomerization of retinol to the 11-cis form involves the hydrolysis of all-trans retinyl esters. Although this is the same process as that occurring in the vertebrate eye, it is different from the retinal photoisomerase reaction known in other arthropods, specifically diurnal insects (Hymenoptera and probably Diptera). Using homogenates of crayfish, we have tested this proposed mechanism by inhibiting retinyl ester synthetase activity in the presence of exogenous all-trans retinol. Inhibition of lecithin:retinol acyl transferase with 5 μmol l-1 retinyl bromoacetate or 2 mmol l-1 phenylmethylsulfonyl fluoride blocks the formation of both all-trans and 11-cis retinyl esters as well as 11-cis retinol, as shown by direct assay and by the decrease in counts derived from tritiated all-trans retinol. The similarity of this isomerization to the mechanism in vertebrate pigment epithelium is thus an interesting example of convergent evolution in the biochemistry of visual pigments, in which the pigments themselves (the opsins) are largely conserved across phyla.
In Vivo Muscle Force–Length Behavior During Steady-Speed Hopping in Tammar Wallabies
Authors: Biewener Andrew A. , Konieczynski David D. , Baudinette Russell V.
Published: April 2021

Moderate to large macropodids can increase their speed while hopping with little or no increase in energy expenditure. This has been interpreted by some workers as resulting from elastic energy savings in their hindlimb tendons. For this to occur, the muscle fibers must transmit force to their tendons with little or no length change. To test whether this is the case, we made in vivo measurements of muscle fiber length change and tendon force in the lateral gastrocnemius (LG) and plantaris (PL) muscles of tammar wallabies Macropus eugenii as they hopped at different speeds on a treadmill. Muscle fiber length changes were less than ±0.5 mm in the plantaris and ±2.2 mm in the lateral gastrocnemius, representing less than 2 % of total fiber length in the plantaris and less than 6 % in the lateral gastrocnemius, with respect to resting length. The length changes of the plantaris fibers suggest that this occurred by means of elastic extension of attached cross-bridges. Much of the length change in the lateral gastrocnemius fibers occurred at low force early in the stance phase, with generally isometric behavior at higher forces. Fiber length changes did not vary significantly with increased hopping speed in either muscle (P>0.05), despite a 1.6-fold increase in muscle–tendon force between speeds of 2.5 and 6.0 m s−1. Length changes of the PL fibers were only 7±4 % and of the LG fibers 34±12 % (mean ± S.D., N=170) of the stretch calculated for their tendons, resulting in little net work by either muscle (plantaris 0.01±0.03 J; gastrocnemius −0.04±0.30 J; mean ± S.D.). In contrast, elastic strain energy stored in the tendons increased with increasing speed and averaged 20-fold greater than the shortening work performed by the two muscles. These results show that an increasing amount of strain energy stored within the hindlimb tendons is usefully recovered at faster steady hopping speeds, without being dissipated by increased stretch of the muscles’ fibers. This finding supports the view that tendon elastic saving of energy is an important mechanism by which this species is able to hop at faster speeds with little or no increase in metabolic energy expenditure.
Partitioning of Oxygen Uptake between the Gills and Skin in Fish Larvae: A Novel Method for Estimating Cutaneous Oxygen Uptake
Authors: Rombough Peter J.
Published: April 2021

The goal of this study was to develop an alternative to the traditional rubber dam method for measuring cutaneous oxygen uptake in bimodally respiring (skin + gills) fish larvae. The method tested involved using microelectrodes to measure the gradient in the diffusive boundary layer adjacent to seven positions on the skin surface (one on the head, two on the yolk sac, two on the trunk, one at the base of the dorsal fin-fold and one on the proximal portion of the caudal fin-fold) of rainbow trout (Oncorhynchus mykiss) larvae in still water. The gradient , where x is the distance from the skin surface) wa.s then used to calculate area-specific rate of O2 uptake according to the Fick equation, , where A is the cross-sectional area of the boundary layer, D is the diffusion coefficient and β is the capacitance coefficient for O2 in water. The accuracy of the method was assessed by comparing it with the rubber dam method. After correcting for differences in body mass, the two methods gave essentially identical results. According to the boundary layer method, the mean (±95 % CI) rate of O2 uptake across the skin of newly hatched rainbow trout at 10 °C is 3.13±0.18 μg O2 cm−2 h−1 (N=265).

The corresponding value obtained using the rubber dam method was 3.36±0.35 μg O2 cm−2 h−1 (N=27). The advantages of the boundary layer method are that it can be used with smaller, more delicate larvae and that variables, such as flow rate, that can affect the efficiency of gas exchange can be regulated more precisely. The boundary layer method also permits examination of regional differences in exchange efficiency, although in still water such differences do not appear to be significant in trout larvae. The mean steepness of the gradient in the boundary layer and, hence, the mean rate of area-specific O2 uptake were essentially the same (P>0.05) at all seven locations tested in this study. The boundary layer method can potentially be used to study the transcutaneous flux, not only of O2 but of virtually any diffusible substance that can be measured with microelectrodes and that is consumed (e.g. Na+, Ca2+) or excreted (e.g. CO2, NH3) by fish larvae or other small organisms.
Burrow Ventilation in the Tube-Dwelling Shrimp Callianassa Subterranea (Decapoda: Thalassinidea): III. Hydrodynamic Modelling and the Energetics of Pleopod Pumping
Authors: Stamhuis Eize J. , Videler John J.
Published: April 2021

The process of flow generation with metachronally beating pleopods in a tubiform burrow was studied by designing a hydrodynamic model based on a thrust–drag force balance. The drag of the tube (including the shrimp) comprises components for accelerating the water into the tube entrance, for adjusting a parabolic velocity profile, for accelerating the flow into a constriction due to the shrimp’s body and another constriction due to the extended tail-fan, for shear due to separation and for the viscous resistance of all tube parts. The thrust produced by the beating pleopods comprises components for the drag-based thrust and for the added-mass-based thrust. The beating pleopods are approximated by oscillating flat plates with a different area and camber during the power stroke and the recovery stroke and with a phase shift between adjacent pleopod pairs. The added mass is shed during the second half of the power stroke and is minimized during the recovery stroke. A force balance between the pleopod thrust and the tube drag is effected by calculating the mean thrust during one beat cycle at a certain flow velocity in the tube and comparing it with the drag of the tube at that flow velocity.

The energetics of the tube and the pump are derived from the forces, and the mechanical efficiency of the system is the ratio of these two. Adjusted to standard Callianassa subterranea values, the model predicts a mean flow velocity in the tube of 1.8 mm s−1. The mean thrust force, equalling the drag, is 36.8 μN, the work done by the pleopod pump per beat cycle is 0.91 μJ and the energy dissipated by the tube system is 0.066 μJ per cycle. The mechanical efficiency is therefore 7.3 %. Pump characteristics that may be varied by the shrimp are the beat frequency, the phase shift, the amplitude and the difference in pleopod area between the power and recovery strokes. These parameters are varied in the model to evaluate their effects. Furthermore, the moment of added mass shedding, the distance between adjacent pleopods, the number of pleopods and the total tube drag were also varied to evaluate their effects.
Stress/Strain Behaviour of the Equine Laminar Junction
Authors: Douglas J. E. , Biddick T. L. , Thomason J. J. , Jofriet J. C.
Published: April 2021

The equine laminar junction plays a vital role in transferring the forces of weight-bearing between the epidermal hoof wall and the bone of the third phalanx, but the way in which it performs this function is poorly understood. Using samples from sites varying proximodistally and circumferentially around the hoof, the stress/strain behaviour of this tissue was characterised in three directions: radial tension and proximodistal and mediolateral shear. The influences of toe angle and length were also examined.

For all three test directions, the modulus of elasticity increased with increasing strain magnitude. The mean modulus of elasticity in tension was 18.25±5.38 MPa (mean ±1 S.D., N=116; mean strain 0.25). In proximodistal shear, the mean shear modulus was 5.38±1.49 MPa (N=76; mean shear strain 0.48) and in mediolateral shear 2.57±0.91 MPa (N=66; mean shear strain 0.81). In many cases, the individual hoof or horse from which the samples were taken significantly affected the value of the modulus, suggesting that mechanical history may affect the material properties of this tissue. Few biologically significant variations with location, toe length or toe angle were unambiguously demonstrated, suggesting that the material properties of the laminar junction are independent of position, despite apparent regional variations in function, and that foot shape is not a major determinant of material properties.
Mechanisms of Thermal Balance in Flying Centris Pallida (Hymenoptera: Anthophoridae)
Authors: Roberts Stephen P. , Harrison Jon F. , Hadley Neil F.
Published: April 2021

Thermoregulation of the thorax is critical for bees and other endothermic insects to achieve high rates of flight muscle power production. However, the mechanisms allowing insects to regulate thorax temperatures during flight are not well understood. To test whether variations in metabolic heat production, evaporation or heat transfer from the thorax to the abdomen contribute to the maintenance of stable body temperatures during flight in the bee Centris pallida, we measured CO2 production, water vapor loss, wingbeat frequency and body segment temperatures during flight at varying air temperatures (Ta). While hovering in the field and while flying in the respirometer, C. pallida males maintain extremely stable, elevated thorax temperatures (45±2 °C; mean ± S.E.M.). Measurements of head, thorax and abdomen temperatures as a function of Ta during hovering flight in the field indicated that C. pallida males were not actively increasing heat transfer from the thorax to the head or abdomen at high Ta values. As Ta increased from 26 to 35 °C, increases in evaporative water loss were relatively small compared with the decrease in carbon dioxide emission. As Ta values increased from 26 to 35 °C, the factorial decreases in metabolic heat production and the elevation of thorax temperature above Ta were closely matched (35 %), suggesting that variation in metabolic heat production is the major mechanism of thermoregulation in flying C. pallida. The thermal effects on rates of water loss and metabolic water production resulted in a strong positive water balance at cooler Ta values, but a strong negative water balance at Ta values above 31 °C. During the first minute of flight in the respirometry chamber, wingbeat frequency was independent of Ta. However, by the fourth minute, there was a significant negative relationship between Ta and wingbeat frequency, which was similar to the thermal relationship observed for wingbeat frequency in the field. These data suggest that, either through homeostatic regulation or resulting secondarily from thermal effects on flight motor properties, variation in metabolic heat production may occur via altered wingbeat kinematics.
The Diversity and Implications of Animal Structural Colours
Authors: Parker Andrew R.
Published: April 2021

Diffraction gratings were believed to be a rare cause of colour in nature. However, surface gratings, which include diffraction gratings and Bragg gratings, appear to occur in many forms within a diversity of animals. Structural colours in general have implications in the study of animal behaviour and evolution.
Activation Patterns and Length Changes in Hindlimb Muscles of the Bullfrog Rana Catesbeiana During Jumping
Authors: Olson John M. , Marsh Richard L.
Published: April 2021

We measured the electromyographic (EMG) activity of seven hindlimb muscles during jumping in the bullfrog Rana catesbeiana. The semimembranosus, gracilis major, gluteus magnus, adductor magnus, cruralis and plantaris longus were consistently active approximately 20–40 ms before any perceptible movement, as indicated by simultaneous video recordings. Activity ended before full extension of the hindlimb and take-off. Activity in the semitendinosus was variable among the jumps recorded. Simultaneous measurements of EMG activity and length changes (via sonomicrometry) in the semimembranosus (SM) and gluteus magnus (GM) muscles indicated that the performance characteristics of these two muscles differed. The SM muscle (a hip extensor) shortens and is activated in a manner consistent with its producing power during a significant fraction of the take-off phase. It shortened by a mean of 26.2 % of the resting length during the propulsive phase of the two longest jumps for each frog. The delay between the onset of EMG activity and the beginning of shortening averaged 24 ms, which was brief compared with that found for the GM. The total strain and mean shortening velocity of the SM increased with jumping distance. Contrary to our initial expectations, the GM muscle does not shorten as one would expect of a muscle involved in powering the jump throughout take-off. This muscle has an extensor action at the knee, but also has a flexor action at the hip. A long delay existed between the onset of EMG activity and the beginning of shortening (46–116 ms among the individuals tested). Shortening during take-off by the GM (a mean of 16.7 % for all jumps) was much less than by the SM, and in many jumps most of this shortening occurred late in the take-off period. Although the GM cannot contribute directly to power output early in take-off, it may contribute to powering the jump indirectly by transferring energy from the hip extensors to the knee joint. We conclude that muscles previously assumed (on the basis of anatomical criteria) by ourselves and others to be powering the jump may show considerable diversity of function. We hypothesize that elastic energy storage is used to help power jumping, and therefore suggest that muscles in series with major tendinous elements should be targeted for further study.