bluuebunny/crossref_metadata_2025 huggingface dataset:
Pilocarpine-Induced Motor Rhythms in the Isolated Locust Suboesophageal Ganglion
Authors: Rast Georg F. , Bräunig Peter
Published: April 2021

Rhythmic activity was recorded from the mandibular motor nerves after treating isolated locust suboesophageal ganglia with the muscarinic agonist pilocarpine. The rhythmic motor pattern consisted of alternating bursts of activity in the antagonistic mandibular opener and closer motoneurones on each side and was synchronised in contralateral homologues. This pattern closely resembled the activity recorded from mandibular muscles in intact feeding locusts. The chewing frequency, however, was approximately three times higher in intact insects than the frequency of the motor pattern recorded from isolated ganglia. Serotonergic neurosecretory cells showed activity synchronous with the pilocarpine-evoked motor pattern. Similarly, rhythmic activity of the motoneurones innervating the two mandibular muscle receptor organs was synchronised with the mandibular motor pattern.
The Locust Dcmd, a Movement-Detecting Neurone Tightly Tuned to Collision Trajectories
Authors: Judge Sarah J. , Rind F. Claire
Published: April 2021

A Silicon Graphics computer was used to challenge the locust descending contralateral movement detector (DCMD) neurone with images of approaching objects. The DCMD gave its strongest response, measured as either total spike number or spike frequency, to objects approaching on a direct collision course. Deviation in either a horizontal or vertical direction from a direct collision course resulted in a reduced response. The decline in the DCMD response with increasing deviation from a collision course was used as a measure of the tightness of DCMD tuning for collision trajectories. Tuning was defined as the half-width of the response when it had fallen to half its maximum level. The response tuning, measured as averaged mean spike number versus deviation away from a collision course, had a half-width at half-maximum response of 2.4 °–3.0 ° for a deviation in the horizontal direction and 3.0 ° for a deviation in the vertical direction. Mean peak spike frequency showed an even sharper tuning, with a half-width at half-maximum response of 1.8 ° for deviations away from a collision course in the horizontal plane.
Cold-Induced Angiogenesis in Seasonally Acclimatized Rainbow Trout (Oncorhynchus Mykiss)
Authors: Egginton Stuart , Cordiner Sandra
Published: April 2021

Seasonal acclimatization of rainbow trout induced an inverse relationship between environmental temperature and the capillary:fibre ratio of slow locomotory muscle, which increased from 1.73±0.09 in the summer (18 °C) to 2.50±0.15 in the winter (4 °C). However, the rate of capillary growth (angiogenesis) was exceeded by that of fibre growth at low temperatures such that the extensive fibre hypertrophy found at 4 °C led to a decrease in capillary density, NA(c,f), to 57 % of that found at 11 °C and 85 % of that at 18 °C. Cold-induced angiogenesis resulted in an expanded capillary bed of similar topology to the existing network, with capillary orientation deviating from that of muscle fibres by only 4–7 %. Capillary length density was maximal at 11 °C, JV(c,f)=2421±239 mm-2, which as previously described corresponds to the point when muscle blood flow is highest and the scope for aerobic swimming is greatest, reflecting an integrated response to optimize aerobic performance at intermediate temperatures. In contrast, ventricular NA(c,f) parallels heart rate and hence was highest at 18 °C, while there was no seasonal variation in myocyte diameter. Although a systemic response to seasonal adjustments in humoral factors may occur, the data reported here suggest that angiogenesis is probably stimulated by different mechanical factors in these two muscles.
An Analysis of Clock-Shift Experiments: is Scatter Increased and Deflection Reduced in Clock-Shifted Homing Pigeons?
Authors: Chappell Jackie
Published: April 2021

Clock-shifting (altering the phase of the internal clock) in homing pigeons leads to a deflection in the vanishing bearing of the clock-shifted group relative to controls. However, two unexplained phenomena are common in clock-shift experiments: the vanishing bearings of the clock-shifted group are often more scattered (with a shorter vector length) than those of the control group, and the deflection of the mean bearing of the clock-shifted group from that of the controls is often smaller than expected theoretically. Here, an analysis of 55 clock-shift experiments performed in four countries over 21 years is reported. The bearings of the clock-shifted groups were significantly more scattered than those of controls and less deflected than expected, but these effects were not significantly different at familiar and unfamiliar sites. The possible causes of the effects are discussed and evaluated with reference to this analysis and other experiments. The most likely causes appear to be conflict between the directions indicated by the sun compass and either unshifted familiar visual landmarks (at familiar sites only) or the unshifted magnetic compass (possible at both familiar and unfamiliar sites).
Lactate accumulation in the shell of the turtle Chrysemys picta bellii during anoxia at 3 °C and 10 °C
Authors: Jackson Donald C.
Published: April 2021

Lactate concentrations were measured in the shell and plasma of the turtle Chrysemys picta bellii after 3 months of submergence anoxia at 3 °C and during and after 9 days of submergence anoxia at 10 °C. Liver and skeletal muscle lactate levels were also measured in control and anoxic animals at each temperature. At 3 °C, mean shell lactate concentration (N=4) reached 133 mmol kg−1 shell mass and plasma lactate levels were 144 mmol l−1; at 10 °C, shell and plasma lactate concentrations (N=5) rose in parallel during anoxic exposure, to 70.8 mmol kg−1 shell mass and 78.9 mmol l−1, respectively, and returned in parallel to control levels during 9 days of recovery. At the end of the anoxic periods, an estimated 44 % of the total body lactate resided in the shell at 3 °C and 43 % at 10 °C, and indirect evidence suggests that the shell buffered these same fractions of the acid load. Because of the high lactate concentration per kilogram of shell water (416 mmol kg−1 at 3 °C; 221 mmol kg−1 at 10 °C) and the known formation of calcium lactate complexes, it is postulated that most of the lactate existed in the shell in combined form. I conclude that sequestration of lactate within the shell represents a potentially major adaptation to anoxic acidosis for this animal and, together with the previously described release of shell carbonates, may account for up to two-thirds of the total lactic acid buffering in this animal.
Forewing asymmetries during auditory avoidance in flying locusts
Authors: Dawson Jeff W. , Dawson-Scully Ken , Robert Daniel , Robertson R. Meldrum
Published: April 2021

Flying locusts orient to sounds in their environment. Sounds similar to those produced by echolocating bats cause a flying locust to change its flight path. We used high-speed cinematography and videography to study changes in body posture and wing kinematics of tethered locusts in response to stimulation with bat-like sounds. Locusts showed both negative and positive phonotaxis to this stimulus. Within a few wingbeats of stimulus onset (between 126 and 226 ms), locusts deflected their abdomens to one side, and the angle of the left and right forewings with respect to the dorsal–ventral body axis became asymmetrical during the downstroke. This forewing asymmetry, in which the forewing on the inside of the turn became more depressed, ranged from 20 to 45 ° (37±9.7 °, mean ± S.D.) and was correlated with the direction and magnitude of abdomen deflection, a measure of steering in tethered, flying locusts. Hindwing stroke angle asymmetries were minimal or non-existent after stimulation. Coincident with changes in forewing asymmetry and abdomen deflection was a decrease in stroke amplitude (19±6.5 °) of the forewing on the inside of the attempted turn. Motor patterns from forewing first basalar (M97) muscles showed an asymmetry in the timing of left and right depressor activation that ranged from 10.4 to 1.6 ms (4.23±2.85 ms). The number of spikes per depressor burst increased to a maximum of three spikes in the muscle on the inside of the attempted turn, and depressor frequency (wingbeat frequency) increased by approximately 2 Hz (2.17±0.26 Hz). We suggest that the asymmetry in forewing first basalar activity is causally related to the asymmetry in the timing of the initiation of the downstroke, resulting in an asymmetry in the ranges of the stroke angles of the forewings, which would impart a roll torque to the locust. This would augment the steering torques generated by concurrent changes in the angle of attack of the fore- and hindwings and changes in abdomen position to effect rapid avoidance manoeuvres.
Urate deposits in the gecarcinid land crab Gecarcoidea natalis are synthesised de novo from Excess dietary nitrogen
Authors: Linton Stuart M. , Greenaway Peter
Published: April 2021

The urate content of the gecarcinid land crab Gecarcoidea natalis was correlated to the amount of nitrogen assimilated. Crabs fed a high-nitrogen diet (ad libitum amounts of soy beans and fig leaves, Ficus macrophylla) for 6 weeks assimilated approximately 23 times more nitrogen (33.9±5.6 mmol kg−1 day−1) than animals fed a diet low in nitrogen (fig leaves alone) (1.5±0.7 mmol kg−1 day−1). Animals maintained on a high-nitrogen diet accumulated urate (67.1±29.4 mmol kg−1 dry mass), while animals fed the low-nitrogen diet did not accumulate significant amounts of urate compared with the control animals killed at the beginning of the dietary period. The urate deposits clearly originate from the excess dietary nitrogen ingested on the high-nitrogen diet. The intake of preformed dietary purine was low (0.028±0.005 mmol kg−1 dry mass) and at most could only account for 0.04 % of the urate accumulated by crabs fed the high-nitrogen diet. This indicates that the urate was synthesised de novo. When crabs were fed a high-nitrogen diet supplemented with [15N]glycine, the 15N heavy isotope was incorporated into urate. This provided direct evidence that the urate was synthesised de novo.
Actual and ‘optimum’ flight speeds: field data reassessed
Authors: Pennycuick C. J.
Published: April 2021

Previously published field observations of the air speeds of 36 species of birds, all observed by the same method (ornithodolite), were compared with estimates of the corresponding minimum power speeds, calculated with a default body drag coefficient of 0.1. This value, which was derived from recent wind tunnel studies, represents a downward revision from default values previously used and leads, in turn, to an upward revision of estimated minimum power speeds. The mean observed air speeds are now distributed around the minimum power speed, rather than in between the speeds for minimum power and maximum range, as they were before. Although the field data do not represent migration, examination of the marginal effects of small changes of speed, on power and lift:drag ratio, indicates that flying at the maximum range speed on migration may not represent an ‘optimal’ or even a practical strategy and that cruising speeds may be limited by the muscle power available or by aerobic capacity. Caution in constructing ‘optimisation’ theories is indicated.
Anti-diuresis in the blood-feeding insect Rhodnius prolixus Stål: the peptide CAP2b and cyclic GMP inhibit Malpighian tubule fluid secretion
Authors: Quinlan Michael C. , Tublitz Nathan J. , O’Donnell Michael J.
Published: April 2021

Rhodnius prolixus eliminates NaCl-rich urine at high rates following its infrequent but massive blood meals. This diuresis involves stimulation of Malpighian tubule fluid secretion by diuretic hormones released in response to distention of the abdomen during feeding. The precipitous decline in urine flow that occurs several hours after feeding has been thought until now to result from a decline in diuretic hormone release. We suggest here that insect cardioacceleratory peptide 2b (CAP2b) and cyclic GMP are part of a novel mechanism of anti-diuresis. Secretion rates of 5-hydroxytryptamine-stimulated Malpighian tubules are reduced by low doses of CAP2b or cyclic GMP. Maximal secretion rates are restored by exposing tubules to 1 mmol l-1 cyclic AMP. Levels of cyclic GMP in isolated tubules increase in response to CAP2b, consistent with a role for cyclic GMP as an intracellular second messenger. Levels of cyclic GMP in tubules also increase as urine output rates decline in vivo, suggesting a physiological role for this nucleotide in the termination of diuresis.
Nutritional Homeostasis in LocUsts: Is There a Mechanism for Increased Energy Expenditure During Carbohydrate Overfeeding?
Authors: Zanotto Flavia P. , Gouveia Scott M. , Simpson Stephen J. , Raubenheimer D. , Calder Phillip C.
Published: April 2021

Maintenance of carbohydrate balance via changes in CO2 output volume was investigated in locusts using a flow-through respirometer. The effect of an imbalance in the dietary protein to digestible carbohydrate ratio on expired CO2 levels was measured in locusts fed one of two synthetic diets [7 % protein, 21 % digestible carbohydrate (7:21) and 21 % protein, 7 % digestible carbohydrate (21:7)]. Additionally, the effect of dietary dilution was investigated by feeding locusts one of two diets with a close-to-optimal ratio of protein to carbohydrate, one containing 7 % protein and 7 % digestible carbohydrate (7:7) and the other containing 21 % protein and 21 % digestible carbohydrate (21:21). For insects fed unbalanced diets, a higher CO2 output volume was measured during feeding on diet 7:21 when compared with insects fed on diet 21:7. Locusts also expired a greater volume of CO2 during the entire 2 h observation period. This response is consistent with specific metabolic control of carbohydrate balance via enhanced respiration. For insects fed balanced diets, the total volume of CO2 expired over the duration of a meal was greater for insects fed diet 7:7 than for those fed diet 21:21, although this was due entirely to meals lasting longer on the more dilute diet. However, the basal level of respiration rate was greater for insects fed diet 21:21 and, as a result, over the entire 2 h period, CO2 output volume did not differ between locusts fed diet 7:7 or 21:21. A possible mechanism for enhanced CO2 output volume on the nutritionally unbalanced diet was investigated, namely triglyceride/fatty-acid substrate cycling. There was no evidence for the presence of the thermogenic effect of this particular cycle on locusts as a means for dealing with excess ingested carbohydrate.
The Effects of Seasonal Hypertrophy and Atrophy on Fiber Morphology, Metabolic Substrate Concentration and Sound Characteristics of the Weakfish Sonic Muscle
Authors: Connaughton M. A. , Fine M. L. , Taylor M. H.
Published: April 2021

Male weakfish Cynoscion regalis possess highly specialized, bilateral, striated sonic muscles used in sound production associated with courtship. Androgen-driven hypertrophy of the muscles during the late spring spawning period results in a tripling of sonic muscle mass followed by post-spawning atrophy. This study examined the morphological and biochemical changes underlying seasonal changes in sonic muscle mass and the functional effects of these on contraction as measured by sound production. Sonic muscle fiber cross-sectional area (CSA) increased significantly during the period of hypertrophy and then decreased by nearly 60 %. Both the CSA of the contractile cylinder and that of the peripheral sarcoplasm decreased significantly by late summer, with the peripheral ring of sarcoplasm virtually disappearing. Muscle protein content followed a similar trend, suggesting a major loss of structural elements during atrophy. Muscle glycogen and lipid content decreased precipitously in early June during the period of maximal sound production. Sound pressure level increased and sound pulse duration decreased with increasing sonic muscle mass, indicating that sonic muscle fibers contract with greater force and shorter duration during the spawning season. Neither the pulse repetition rate nor the number of pulses varied seasonally or with muscle mass, suggesting that the effects of steroids on the acoustic variables are more pronounced peripherally than in the central nervous system. Seasonal sonic muscle hypertrophy, therefore, functions as a secondary sexual characteristic that maximizes vocalization amplitude during the spawning period.
Changing Patterns of Vasculature in the Developing Amphibian Retina
Authors: Dunlop S. A. , Moore S. R. , Beazley L. D.
Published: April 2021

Patterns of vascularisation were examined in whole-mounted retinae from tadpole stages to adulthood in the tree frog Litoria moorei using perfusion with Indian ink. Changing cell densities in the underlying ganglion cell layer were studied in a parallel Cresyl-stained series. Throughout development, the vasculature was pan-retinal and the hyaloid vessel was prominent. In early tadpole stages, capillaries were arranged as a honeycomb, and their number increased at a rate sufficient to maintain high densities in the face of increasing retinal area; major arteries and veins condensed within the capillary network. By early post-metamorphic life, the retinal vasculature was remodelled by the loss of four-fifths of the capillaries; the reduction in their density was far greater than could be accounted for by continuing retinal growth. This loss resulted in a change from the honeycomb appearance to one with largely parallel vessels linked by fewer connecting ones, an arrangement that became increasingly pronounced. In post-metamorphic life, the number of branch points increased such that their density decreased only slightly in the face of considerable increases in retinal area. The density of branch points varied across the retina and changed with age. Initially, the vasculature was most dense centrally, but by mid-larval life densities were highest in two patches located in the mid-temporal and mid-nasal retina. Thereafter, the vasculature increasingly assumed gradients resembling an area centralis and visual streak, a profile that survived the vascular remodelling. The development of density gradients in the vasculature preceded that of cells in the ganglion cell layer, the latter appearing only following metamorphosis. However, in post-metamorphic life, the topographies of the retinal vasculature and cells in the ganglion cell layer were closely related.
Locomotion On The Water Surface: Propulsive Mechanisms Of The Fisher Spider Dolomedes Triton
Authors: Suter Robert B. , Rosenberg Oren , Loeb Sandra , Wildman Horatio , Long John H.
Published: April 2021

Using kinematic and mechanical experiments, we have shown how fisher spiders, Dolomedes triton (Araneae, Pisauridae), can generate horizontal propulsive forces using their legs. This horizontal thrust is provided primarily by the drag of the leg and its associated dimple as both move across the water surface. Less important sources of resistance are surface tension and bow waves. The relative contributions of drag, surface tension and bow waves were examined in several different ways. In one experiment, we measured the forces acting on a leg segment as water flowed past it in non-turbulent flow; the bow wave was not present at leg relative velocities below 0.2 m s−1 and thus cannot play a role in thrust production at low leg speeds. In a second experiment, we varied the surface tension by altering the concentration of ethanol from 0 % to 9 % in the experimental water tank. At a constant dimple depth, force varied little with changes in surface tension, a result consistent with the hypothesis that drag is the primary source of resistance. In addition, however, as surface tension decreased from 0.072 to 0.064 N m−1, the power exponent of the relationship between force and velocity (as measured by the exponent of the power function relating the two variables) increased; at lower surface tensions, down to 0.054 N m−1, the power exponent of the relationship between force and velocity decreased. These results suggest an influence of surface tension (albeit still secondary to drag) in generating horizontal resistance to leg movement. We also measured flow disturbance in the water downstream from a leg segment and confirmed that, even at velocities well below 0.2 m s−1, the leg-cum-dimple transferred momentum to the water, which is a clear indication that drag is a contributor to the resistance encountered by a spider’s leg. Finally, modeling the leg-cum-dimple as a circular cylinder generates values of drag that account for 75–98 % of the measured leg force when the dimple is 0 or 1 mm deep. These results not only elucidate the primary mechanism of propulsion for D. triton and other similar-sized arthropods, such as adult water striders (Gerridae), but also suggest that the formerly enigmatic locomotion of very small water-walking organisms (e.g. first-instar water striders) can be understood in the same way.
Intracellular Ca2+ Release Mediated by Metabotropic Glutamate Receptor Activation In The Leech Giant Glial Cell
Authors: Lohr Christian , Deitmer Joachim W.
Published: April 2021

We have investigated the effects of glutamate and glutamate receptor ligands on the intracellular free Ca2+ concentration ([Ca2+]i) and the membrane potential (Em) of single, identified neuropile glial cells in the central nervous system of the leech Hirudo medicinalis. Exposed glial cells of isolated ganglia were filled iontophoretically with the Ca2+ indicator dye Fura-2. Application of glutamate (200–500 μmol l−1) caused biphasic membrane potential shifts and increases in [Ca2+]i, which were only partly reduced by either removing extracellular Ca2+ or blocking ionotropic glutamate receptors with 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 50–100 μmol l−1). Metabotropic glutamate receptor (mGluR) ligands had the following rank of potency in inducing a rise in [Ca2+]i: quisqualate (QQ, 200 μmol l−1) > glutamate (200 μmol l−1) > L(+)2-amino-3-phosphonopropionic acid (L-AP3, 200 μmol l−1) > trans-1-aminocyclopentane-1,3-dicarboxylic acid (t-ACPD, 400 μmol l−1). The mGluR-selective antagonist (RS)-α-methyl-4-carboxyphenylglycine [(RS)-MCPG, 1 mmol l−1] significantly reduced glutamate-evoked increases in [Ca2+]i by 20 %. Incubation of the ganglia with the endoplasmic ATPase inhibitor cyclopiazonic acid (CPA, 10 μmol l−1) caused a significant (53 %) reduction of glutamate-induced [Ca2+]i transients, while incubation with lithium ions (2 mmol l−1) resulted in a 46 % reduction. The effects of depleting the Ca2+ stores with CPA and of CNQX were additive. We conclude that glutamate-induced [Ca2+]i transients were mediated by activation of both Ca2+-permeable ionotropic non-NMDA receptors and of metabotropic glutamate receptors leading to Ca2+ release from intracellular Ca2+ stores.
Molecular Genetic Analysis of V-ATPase Function in Drosophila Melanogaster
Authors: Dow Julian A. T. , Davies Shireen A. , Guo Yiquan , Graham Shirley , Finbow Malcolm E. , Kaiser Kim
Published: April 2021

V-ATPases are phylogenetically widespread, highly conserved, multisubunit proton pumps. Originally characterised in endomembranes, they have been found to energise transport across plasma membranes in a range of animal cells and particularly in certain epithelia. While yeast is the model of choice for the rapid generation and identification of V-ATPase mutants, it does not allow their analysis in a plasma membrane context. For such purposes, Drosophila melanogaster is a uniquely suitable model. Accordingly, we have cloned and characterised genes encoding several V-ATPase subunits in D. melanogaster and, using P-element technology, we have succeeded in generating multiple new alleles. Reporter gene constructs reveal ubiquitous expression, but at particularly high levels in those epithelia thought to be energised by V-ATPases, and several of the alleles have lethal recessive phenotypes characterised by epithelial dysfunction. These results, while providing the first gene knockouts of V-ATPases in animals, also illustrate the general utility of D. melanogaster as a model for the genetic analysis of ion transport and its control in epithelia.
The Key Role of the H+ V-ATPase in Acid–Base Balance and Na+ Transport Processes in Frog Skin
Authors: Ehrenfeld Jordi , Klein Ulla
Published: April 2021

Frogs are faced with various osmoregulatory problems, such as compensation of salt and water loss or metabolic acidification. Being exposed both to air and to pond water of low salinity in their natural habitat, the epithelium of the frog skin serves as one of the major organs for body fluid homeostasis. For years, the frog skin has been the guiding model for ion transport processes in animal cells energized by a Na+-motive force. Meanwhile, however, it was demonstrated that under natural conditions Na+ uptake is electrically coupled to active H+ secretion, mediated by an electrogenic H+ pump. A proton-motive force generated at the apical membrane of the mitochondria-rich cells (MR cells) energizes Na+ entry via apical Na+ channels. The basolateral Na+/K+ P-ATPase then pumps Na+ out of the cell into the body fluid. Thus, there are two pumps functioning in series, both involved in transepithelial Na+ transport.

Our recent investigations provided conclusive evidence that the H+ pump of the frog skin is an H+ V-ATPase. In transport studies, Na+ absorption and H+ secretion were blocked by micromolar concentrations of bafilomycin A1 or concanamycin A, two highly specific inhibitors of H+ V-ATPases. Using immunofluorescence microscopy, H+-V-ATPase-like immunoreactivity was found in MR cells in the region of their apical membrane foldings and intracellularly in the apical portion of the cell at so far unidentified locations. Besides the definition of its molecular nature, these results also confirmed the localization of the H+ pump in the apical membrane of the MR cells. These cells were already candidates for H+-V-ATPase localization mostly from correlations between their morphological features and their epithelial H+ secretion capacity. So far, there is evidence for only one type of MR cell serving both H+ and HCO3− secretion through an apical Cl−/HCO3− antiporter.

H+-V-ATPase-mediated H+ secretion and thus Na+ absorption can be modulated by complementary mechanisms. Changes in intracellular H+ concentration linked to the animal’s acid–base status will directly influence H+ V-ATPase activity. Acute acidification increases H+ current, probably as a result of the insertion of H+-V-ATPase-bearing vesicles by exocytotic processes, while alkalization causes the reverse effects. Chronic metabolic acidosis induces an increase in MR cell number in response to hormonal signals.
The Renal Electrogenic Na+:HCO3− Cotransporter
Authors: Boron Walter F. , Hediger Matthias A. , Boulpaep Emile L. , Romero Michael F.
Published: April 2021

The electrogenic Na+:HCO3− cotransporter (symporter) is the major transporter for HCO3− reabsorption across the basolateral membrane of the renal proximal tubule and also contributes significantly to Na+ reabsorption. We expression-cloned the salamander renal electrogenic Na+:Bicarbonate Cotransporter (NBC) in Xenopus laevis oocytes. After injecting poly(A)+ RNA, fractionated poly(A)+ RNA or cRNA, we used microelectrodes to monitor membrane potential (Vm) and intracellular pH (pHi). All solutions contained ouabain to block the Na+/K+ pump (P-ATPase). After applying 1.5 % CO2/10 mmol l−1 HCO3− (pH 7.5) and allowing pHi to stabilize from the CO2-induced acidification, we removed Na+. In native oocytes or water-injected controls, removing Na+ hyperpolarized the cell by −5 mV and had no effect on pHi. In oocytes injected with poly(A)+ RNA, removing Na+ transiently depolarized the cell by −10 mV and caused pHi to decrease; both effects were blocked by 4,4′-diisothiocyano-2,2′-stilbenedisulfonate (DIDS) and required HCO3−. We enriched the signal by electrophoretic fractionation of the poly(A)+ RNA, and constructed a size-selected cDNA library in pSPORT1 using the optimal fraction. Screening the Ambystoma library yielded a single clone (aNBC). Expression was first obvious 3 days after injection of NBC cRNA. Adding CO2/HCO3− induced a large (>50 mV) and rapid hyperpolarization, followed by a partial relaxation as pHi stabilized. Subsequent Na+ removal depolarized the cell by more than 40 mV and decreased pHi. aNBC is a full-length clone with a start Met and a poly(A)+ tail; it encodes a protein with 1025 amino acids and several putative membrane-spanning domains. aNBC is the first member of a new family of Na+-linked HCO3− transporters. We used aNBC to screen a rat kidney cDNA library, and identified a full-length cDNA clone (rNBC) that encodes a protein of 1035 amino acids. rNBC is 86 % identical to aNBC and can be functionally expressed in oocytes.
Elementary and Global Aspects of Calcium Signalling
Authors: Berridge Michael J.
Published: April 2021

Calcium is a ubiquitous second messenger used to regulate a wide range of cellular processes. This role in signalling has to be conducted against the rigid homeostatic mechanisms that ensure that the resting level of Ca2+ is kept low (i.e. between 20 and 100 nmol l−1) in order to avoid the cytotoxic effects of a prolonged elevation of [Ca2+]. Cells have evolved a sophisticated signalling system based on the generation of brief pulses of Ca2+ which enables this ion to be used as a messenger, thus avoiding its toxic effects. Such Ca2+ spikes usually result from the coordinated release of Ca2+ from internal stores using either inositol 1,4,5-trisphosphate or ryanodine receptors. Using Ca2+ imaging techniques, the opening of individual channels has now been visualized and models have been proposed to explain how these elementary events are coordinated to generate the global Ca2+ signals that regulate cellular activity.
Homeostasis Of Energy Conduction, Neurotransmitters, Cytotoxic Compounds And Metal Ions
Authors: Nelson Nathan
Published: April 2021

Communication among unconnected cells requires the release of extracellular messengers and specific receptor mechanisms on, or in, the target cells. Signalling substances include hormones, neurotransmitter substances, trophic factors and diffusible substances. In higher organisms, synaptic transmission is the principal method of communication between cells, especially in the nervous system. Nerve cells mediate fast signalling between sensory systems and the central nervous system (CNS) and between the CNS and effector systems. Within the CNS, nerve cells form complex circuits that serve the integration of inputs and the generation of specific activity patterns. Synaptic transmission is the most important means by which nerve cells communicate. There are two principal types of synaptic transmission; electrical and chemical. Electrical transmission involves ion fluxes across membranes. In many cases, synaptic transmission is chemical and involves the secretion of signalling substances. In most cases, the termination of chemical transmission is achieved by rapid uptake of the released neurotransmitter by specific high-affinity neurotransmitter transporters into the synaptic terminal or the surrounding glial cells (Kuhar, 1973; Iversen and Kelly, 1975; Kanner, 1983, 1989; Kanner and Schuldiner, 1987). It has been known for many years that neurones and glia can accumulate neurotransmitters by Na+-dependent transport processes. Neurotransmitters are cotransported with Na+ utilizing the energy stored in transmembrane electrochemical gradients generated by primary ion pumps (Kanner, 1983). Studies on neurotransmitter uptake have demonstrated the existence of multiple uptake systems, each relatively selective for a specific neurotransmitter. Neurotransmitters are transported across membranes by at least four distinct families of transporters: (1) vesicular transporters that function in the uptake of neurotransmitters into synaptic vesicles and granules (Schuldiner, 1994); (2) Na+- and Cl−-dependent (Na+/Cl−) transporters that operate on the plasma membrane of neuronal and glia cells (Uhl, 1992; Schloss et al. 1992; Amara and Kuhar, 1993); (3) Na+/K+-dependent transporters that function on the plasma membranes, especially in glutamate transport (Kanner, 1993); and (4) general amino acid transport systems that participate in controlling the availability of neurotransmitters outside the cells (McGivan and Pastor-Anglada, 1994).
Flight and size constraints: hovering performance of large hummingbirds under maximal loading
Authors: Chai Peng , Millard David
Published: April 2021

As the smallest birds, hummingbirds are the only birds capable of prolonged hovering. This suggests that hovering locomotion scales unfavourably with size. Is the hovering performance of larger hummingbird species more constrained by size than that of smaller ones? Maximal load-lifting capacities of the two largest species of hummingbirds found in the United States, the blue-throated (Lampornis clemenciae, 8.4 g) and magnificent (Eugenes fulgens, 7.4 g) hummingbird, as well as the two other local small species, the black-chinned (Archilochus alexandri, 3.0 g) and rufous (Selasphorus rufus, 3.3 g) hummingbird, were determined under conditions of short-burst performance. The power reserves of hummingbirds are substantial relative to normal hovering performance. The two large species lifted maximal loads close to twice their body mass for a very brief duration of over 0.4 s. The small species lifted maximal loads approximately equal to their own mass with a longer duration of over 0.6 s. For the two large species under maximal loading, estimates of burst muscle mass-specific mechanical power output assuming perfect elastic energy storage averaged 309 W kg−1, compared with 75 W kg−1 during free hovering without loading. For the two small species, these values were 228W kg−1 and 88 W kg−1, respectively. The differences in aerodynamic force production and power output between the large and small size classes occur despite their similar wing stroke velocity. This indicates that, during burst performance in these hummingbirds, the larger ones had a higher load-lifting capacity and generated more muscle power. In spite of the twofold difference in body mass, both large and small hummingbirds have evolved to become potent aerial competitors in order to exploit their common food resource, nectar. Both size classes have evolved to cope with the multi-dimensional effects of size constraining their aerodynamics, muscle mechanics, metabolism and ecology.
Mitochondrial arginine kinase in the midgut of the tobacco hornworm (Manduca sexta)
Authors: Chamberlin M. E.
Published: April 2021

Mitochondria isolated from the posterior midgut of the tobacco hornworm (Manduca sexta) contain arginine kinase. The distribution of mitochondrial and cytoplasmic marker enzymes indicates that the presence of mitochondrial arginine kinase is not due to cytoplasmic contamination. Arginine is not oxidized by the midgut mitochondria but, when metabolic substrates and ATP are present, respiration can be initiated by the addition of arginine. Under these conditions, there is no return to State 4 respiration, indicating regeneration of ADP by the arginine kinase reaction. Respiration can be blocked, however, by atractyloside, an inhibitor of the adenine nucleotide translocator. These results indicate that arginine kinase resides outside the matrix. Mitochondrial arginine kinase is specific to L-arginine since analogs of L-arginine are ineffective in stimulating respiration in the presence of ATP. Coupling between the adenine nucleotide translocator and arginine kinase was investigated using kinetic and thermodynamic approaches. There were no differences in the activities of arginine kinase in respiring and non-respiring mitochondria when they were measured at different ATP or arginine concentrations. This result indicates that arginine kinase does not have preferential access to the ATP exported out of the matix. A comparison of the apparent equilibrium constant and the mass action ratio of the arginine kinase reaction also confirms that there is no microcompartmentation of the reaction.
Do Flatfish Feed Like Other Fishes? a Comparative Study of Percomorph Prey-Capture Kinematics
Authors: Gibb Alice C.
Published: April 2021

The kinematics of prey capture in two bilaterally asymmetrical pleuronectiform flatfish species (Pleuronichthys verticalis and Xystreurys liolepis) and two symmetrical percomorph species (Lepomis macrochirus, a centrarchid, and Cheilinus digrammus, a labrid) were compared to test the hypothesis that flatfish have distinct prey-capture kinematics from those quantified for other percomorph fishes. Size-matched individuals of both flatfish species were video-taped feeding using a high-speed video system. Cephalic displacement and timing variables were quantified and compared with data from similarly sized L. macrochirus and C. digrammus previously collected by other researchers using similar experimental methodology. Nested multivariate analyses of variance indicated that there was no significant difference in prey-capture kinematics between flatfish and non-flatfish taxa, but that prey-capture kinematics did differ among the four taxa. Multiple nested analyses of variance revealed that the taxa differed in 7 of 11 kinematic variables. Post-hoc tests and comparisons with other fish taxa suggest that individuals of P. verticalis possess an unusual combination of prey-capture kinematics including large hyoid depression, large neurocranial rotation, large upper jaw protrusion and small gape. Previous research has suggested that this combination of traits is associated with suction-based prey capture. Correspondingly, the ram–suction index calculated for P. verticalis is more negative (indicating a greater use of suction) than that calculated for the other taxa. When homologous kinematic variables are compared across these four taxa, flatfish do not appear to have similar prey-capture kinematics. However, both flatfish species are distinct from the two symmetrical percomorph species in their asymmetrical jaw movements.
Work and Power Output in the Hindlimb Muscles of Cuban Tree Frogs Osteopilus Septentrionalis During Jumping
Authors: Peplowski Matthew M. , Marsh Richard L.
Published: April 2021

It has been suggested that small frogs use a catapult mechanism to amplify muscle power production during the takeoff phase of jumping. This conclusion was based on an apparent discrepancy between the power available from the hindlimb muscles and that required during takeoff. The present study provides integrated data on muscle contractile properties, morphology and jumping performance that support this conclusion. We show here that the predicted power output during takeoff in Cuban tree frogs Osteopilus septentrionalis exceeds that available from the muscles by at least sevenfold. We consider the sartorius muscle as representative of the bulk of the hindlimb muscles of these animals, because this muscle has properties typical of other hindlimb muscles of small frogs. At 25 °C, this muscle has a maximum shortening velocity (Vmax) of 8.77±0.62 L0 s−1 (where L0 is the muscle length yielding maximum isometric force), a maximum isometric force (P0) of 24.1±2.3 N cm−2 and a maximum isotonic power output of 230±9.2 W kg−1 of muscle (mean ± S.E.M.). In contrast, the power required to accelerate the animal in the longest jumps measured (approximately 1.4 m) is more than 800 W kg−1 of total hindlimb muscle. The peak instantaneous power is expected to be twice this value. These estimates are probably conservative because the muscles that probably power jumping make up only 85 % of the total hindlimb muscle mass. The total mechanical work required of the muscles is high (up to 60 J kg−1), but is within the work capacities predicted for vertebrate skeletal muscle. Clearly, a substantial portion of this work must be performed and stored prior to takeoff to account for the high power output during jumping. Interestingly, muscle work output during jumping is temperature-dependent, with greater work being produced at higher temperatures. The thermal dependence of work does not follow from simple muscle properties and instead must reflect the interaction between these properties and the other components of the skeletomuscular system during the propulsive phase of the jump.
Survival of Energy Failure in the Anoxic Frog Brain: Delayed Release of Glutamate
Authors: Lutz Peter L. , Reiners Raymond
Published: April 2021

This study investigated the relationship between energy failure and neurotransmitter release in the frog (Rana pipiens) brain during 1–3 h of anoxia. Unlike truly anoxia-tolerant species, the frog does not defend its brain energy charge. When exposed to anoxia at 25 °C, there is an immediate fall in brain ATP levels, which reach approximately 20 % of normoxic levels in approximately 60 min. The frog, nevertheless, survives another 1–2 h of anoxia. At 100 min of anoxia, there is an increase in extracellular adenosine concentration, probably originating from the increased intracellular adenosine concentration caused by the breakdown of intracellular ATP. Increases in the levels of extracellular glutamate and

GABA do not occur until 1–2 h after ATP depletion. This response is quite unlike that recorded for other vertebrates, anoxia-tolerant or anoxia-intolerant, where energy failure quickly results in an uncontrolled and neurotoxic release of excitatory neurotransmitters. In the frog, the delay in excitotoxic neurotransmitter release may be one of the factors that allow a period of survival after energy failure. Clearly, energy failure by itself is not a fatal event in the frog brain.
Voltage Sensing in Jellyfish Shaker K+ Channels
Authors: Grigoriev Nikita G. , Spafford J. David , Gallin Warren J. , Spencer Andrew N.
Published: April 2021

The S4 segment of the jellyfish (Polyorchis penicillatus) Shaker channel jShak1 contains only six positively charged motifs. All other Shaker channels, including the jellyfish Shaker channel jShak2, have seven charges in this segment. Despite their charge differences, both these jellyfish channels produce currents with activation and inactivation curves shifted by approximately +40 mV relative to other Shaker currents.

Adding charge without changing segment length by mutating the N-terminal side of jShak1 S4 does not have a pronounced effect on channel activation properties. Adding the positively charged motif RIF on the N-terminal side of K294 (the homologue of K374 in Drosophila Shaker, which is a structurally critical residue) produced a large positive shift in both activation and inactivation without altering the slope of the activation curve of the channel. When IFR was added to the other side of K294, there was a small negative shift in activation and fast inactivation of the channel was prevented.

Our results demonstrate that K294 divides the S4 segment into functionally different regions and that the voltage threshold for activation and inactivation of the channel is not determined by the total charge on S4.
Cell Membrane Lipid Composition and Distribution: Implications for Cell Function and Lessons Learned From Photoreceptors and Platelets
Authors: Boesze-Battaglia Kathleen , Schimmel Richard J.
Published: April 2021

Photoreceptor rod cells and blood platelets are remarkably different, yet both illustrate a similar phenomenon. Both are strongly affected by membrane cholesterol, and the distribution of cholesterol in the membranes of both cell types is determined by the lipid composition within the membranes. In rod cells, cholesterol strongly inhibits rhodopsin activity. The relatively higher level of cholesterol in the plasma membrane serves to inhibit, and thereby conserve, the activity of rhodopsin, which becomes fully active in the low-cholesterol environment of the disk membranes of these same cells. This physiologically important partitioning of cholesterol between disk membranes and plasma membranes occurs because the disk membranes are enriched with phosphatidylethanolamine, thus providing a thermodynamically unfavorable environment for the sterol. Cholesterol enrichment of platelets renders these cells more responsive to stimuli of aggregation. Stimuli for platelet aggregation cause a rapid transbilayer movement of cholesterol from the outer monolayer. This stimulus-dependent redistribution of cholesterol appears to result from the concomitant movement of phosphatidylethanolamine into the outer monolayer. The attractive, yet still unproven, hypothesis is that cholesterol translocation plays an important role in the overall platelet response and is intimately related to the sensitizing actions of cholesterol on these cells.
Behavioural Analysis of Olfactory Conditioning in the Moth Spodoptera Littoralis (Boisd.) (Lepidoptera: Noctuidae)
Authors: Fan Ruey-Jane , Anderson Peter , Hansson Bill S.
Published: April 2021

We studied the associative learning capabilities for behaviourally relevant cues in the moth Spodoptera littoralis. The moths were trained to associate a conditioned stimulus (CS), geraniol odour, with an unconditioned stimulus (US), a sucrose solution. The occurrence of a proboscis extension reflex (PER) was tested. The PER performance during acquisition increased steadily with the number of training trials. Non-associative control procedures did not result in learning. PER conditioning was achieved when the CS was presented 1–3 s before the US. A wide range of inter-trial intervals was able to support conditioning. Males and females learned equally well. Moths could to some degree learn the CS–US association after a single trial. These results demonstrate that S. littoralis females and males have a good capability to associate an odour with a reward. The neural basis of olfactory coding in moths has been well studied; thus, the moth provides a powerful system in which to examine the neurobiology of olfactory learning.
L-Glutamate and Serotonin are Endogenous in Squid Chromatophore Nerves
Authors: Messenger J. B. , Cornwell C. J. , Reed C. M.
Published: April 2021

Colour changes in cephalopods are controlled by complex organs termed chromatophores whose radial muscles are directly innervated from the brain. In the squids Alloteuthis subulata and Loligo vulgaris, light microscopy of silver- or Methylene-Blue-stained preparations shows that each muscle is innervated by 2–6 nerves running along its length. An electron microscope (EM) study shows that most of these nerves contain 50 nm diameter electron-lucent vesicles organised into numerous synapses along the muscle. Their size and appearance is consistent with their containing L-glutamate (L-Glu). Usually there is one nerve on each muscle containing 95 nm diameter electron-dense vesicles that are not organised into synapses. Such vesicles, whose appearance is consistent with their containing serotonin (5-HT), are never found co-localised with the small, clear vesicles.

Topically applied L-Glu causes the radial muscles to contract (and the chromatophore to expand), even after chronic denervation; this effect is blocked by the glutamate antagonists CNQX and DNQX. In contrast, topically applied 5-HT (or its agonists 8-OH-DOPAT and α-methyl 5-HT) induces relaxation of precontracted muscle. Incubation with antibodies to L-Glu (Lg-A), using peroxidase anti-peroxidase/diaminobenzidine visualisation, produces specific staining along the radial muscles like that seen with silver. Antibodies to 5-HT produce similar specific staining. When sections of skin that had stained positively with Lg-A in the light microscope are examined at the EM level, it is seen that such staining is confined to nerve axons.

These results, showing that L-Glu and 5-HT are endogenous in the nerves innervating squid chromatophores and that the radial muscles contain receptors for both substances, suggest that L-Glu is an excitatory transmitter at squid chromatophore muscles. The way in which 5-HT acts to relax the muscles, however, remains to be established.