bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transfer of the Heart Pacemaker During Juvenile Development in the Isopod Crustacean Ligia Exotica
Authors: Yamagishi Hiroshi , Hirose Euichi 
Published: April 2021

ABSTRACT
Developmental changes in heartbeat pacemaker mechanisms were examined electrophysiologically in the isopod crustacean Ligia exotica. The heartbeat of embryos and early juveniles was myogenic. The heart muscle cells were coupled electrically, and no localized pacemaker activity was found in the heart. In newly hatched juveniles, the cardiac ganglion exhibited no spontaneous activity, although stimulation of the cardiac ganglion produced excitatory junctional potentials (EJPs) in the heart muscle. The myogenic activity of the heart was reset and entrained by the EJPs evoked by ganglionic stimulation. During juvenile development, spontaneous EJPs appeared irregularly in the heart muscle. Later in development, the cardiac ganglion started rhythmic bursting, and each muscle response followed a ganglionic burst discharge and overlapped the EJPs evoked by ganglionic activity. At this point, the activity of the cardiac ganglion was suppressed by application of tetrodotoxin (TTX); however, even in old adults, both muscle activity and the heartbeat continued following TTX application. Heartbeat frequency was lower in TTX-containing saline than in normal saline. These results show that, during juvenile development, the heart pacemaker is transferred from the heart muscle to the cardiac ganglion, which becomes the primary pacemaker and entrains the heart muscle activity to a higher frequency via EJPs.
The Influence of Proprioceptors Signalling Tibial Position and Movement on the Kick Motor Programme in the Locust
Authors: Jellema T. , Heitler W. J. 
Published: April 2021

ABSTRACT
Four main proprioceptors monitor tibial position in the hindleg of the locust: the femoral chordotonal organ (FCO), the lump receptor, the suspensory ligament receptors and Brunner’s organ. The influence of these proprioceptors on quantitative aspects of the kick motor programme has been investigated. The parameters measured were the duration of the initial flexion burst, the duration of co-activation of flexor and fast extensor tibiae (FETi) motoneurones, the number of FETi spikes during the co-activation, the interval between the kick and post-kick flexion, the number of FETi spikes occurring in this interval and the duration of post-kick flexion activity. The lump receptor and Brunner’s organ have no detectable effect on any of these parameters. The FCO has highly significant effects on the duration of both initial flexion and post-kick flexion bursts, and on the number of FETi spikes occurring after the moment of tibial extension. The suspensory ligament receptors have significant effects upon the number of FETi spikes after the kick and the interval between the kick and the post-kick flexion. However, no proprioceptor had any influence upon the duration of co-activation or the number of FETi spikes during the co-activation. Thus, although elements of the kick motor programme preceding and following co-activation are strongly influenced by proprioceptors monitoring tibial position and movement, the co-activation stage, which is central to the effectiveness of the complete behaviour pattern, is not affected.
The Scaling and Potential Importance of Cutaneous and Branchial Surfaces in Respiratory Gas Exchange in Larval and Juvenile Walleye Stizostedion Vitreum
Authors: Rombough Peter J. , Moroz Brenda M. 
Published: April 2021

ABSTRACT
Measurements were made of the surface areas (As) of the skin and gills of larval and juvenile walleye Stizostedion vitreum with a body mass (M) of between 2 mg (1 day post hatch) and 2.3 g (98 days post hatch). The skin, with a relative surface area (As/M) of approximately 8500 mm2 g−1, accounted for more than 99.9 % of the total surface area (skin + gills) at 1 day post hatch. The relative area of the skin decreased as fish grew at an allometric rate of b−1=−0.32±0.01 (mean ± S.E.M., where b−1 is the specific-mass exponent in the allometric equation Y×M−;1=aMb−;1, in which Y is surface area and a is a constant). The relative surface area of the gills (filaments + lamellae) increased in a hyperbolic fashion from very low levels (approximately 5 mm2 g−1) at 1 day post hatch to reach a maximum of approximately 1100 mm2 g−1 at a body mass of approximately 200 mg. Thereafter, relative gill area declined at an allometric rate of b−;1=−;0.19±0.10 (mean ± S.E.M.). Gill area, because it declined at a slower relative rate, finally exceeded skin area at a body mass of approximately 700 mg. The relative surface area of the skin and gills combined (total surface area) decreased at a more- or-less constant allometric rate of b−;1=−;0.21±0.01 (mean ± S.E.M.) throughout the experimental period. On the basis of the allometric rates of expansion, the structural capacity to supply oxygen (b−;1=−;0.19; total gill area, this study) and metabolic demand for oxygen (b−;1≈−;0.13; mean literature value for routine and resting metabolism) appear to remain fairly closely matched in postlarval walleye (&gt;300 mg). The two parameters do not display the same degree of concordance during larval development. In larvae, total respiratory surface area declines on a mass-specific basis at roughly the same rate (b−;1=−;0.21) as gill area does in older fish but, unlike in older fish, metabolic demand for oxygen does not change (b−;1≈0.0). This results in a progr. essive decline in effective respiratory surface area (As/MO2) but does not affect O2 uptake, probably because larvae are so small that surface area is not the limiting factor in gas exchange. Analysis of data from the literature suggests that surface area typically becomes limiting at a body mass of approximately 100 mg. The major function of gills in smaller larvae (&lt;100 mg) appears to involve ionoregulation or related aspects of acid–base balance rather than respiratory gas exchange.
Random Array of Colour Filters in the Eyes of Butterflies
Authors: Arikawa Kentaro , Stavenga Doekele G. 
Published: April 2021

ABSTRACT
The compound eye of the Japanese yellow swallowtail butterfly Papilio xuthus is not uniform. In a combined histological, electrophysiological and optical study, we found that the eye of P. xuthus has at least three different types of ommatidia, in a random distribution. In each ommatidium, nine photoreceptors contribute microvilli to the rhabdom. The distal two-thirds of the rhabdom length is taken up by the rhabdomeres of photoreceptors R1–R4. The proximal third consists of rhabdomeres of photoreceptors R5–R8, except for the very basal part, to which photoreceptor R9 contributes. In all ommatidia, the R1 and R2 photoreceptors have a purple pigmentation positioned at the distal tip of the ommatidia. The R3–R8 photoreceptors in any one ommatidium all have either yellow or red pigmentation in the cell body, concentrated near the edge of the rhabdom. The ommatidia with red-pigmented R3–R8 are divided into two classes: one class contains an ultraviolet-fluorescing pigment. The different pigmentations are presumably intimately related to the various spectral types found previously in electrophysiological studies.
Control of Venom Production and Secretion by Sympathetic Outflow In The Snake Bothrops Jararaca
Authors: Yamanouye N. , Britto L. R. G. , Carneiro S. M. , Markus R. P. 
Published: April 2021

ABSTRACT
Many studies have examined the morphological and biochemical changes in the secretory epithelium of snake venom glands after a bite or milking. However, the mechanisms of venom production and secretion are not yet well understood. The present study was undertaken to evaluate the role of the sympathetic nervous system in the control of venom production and secretion.
Venom glands were obtained from Bothrops jararaca (Viperidae) snakes, either unmilked previously or milked 4, 7 or 15 days before they were killed. Levels of tyrosine-hydroxylase-like immunoreactivity were higher in venom glands collected 4 days after milking, coinciding with the maximal synthetic activity of the secretory cells. The only catecholamine detected by high-performance liquid chromatography was noradrenaline, indicating the presence of noradrenergic fibres in these glands. In reserpine-treated milked snakes, no venom could be collected, and electron microscopic analysis showed narrow rough endoplasmic reticulum cisternae, instead of wide cisternae, and less well-developed Golgi apparatus compared with milked untreated snakes, indicating impairment of protein synthesis and secretion. The administration of isoprenaline or phenylephrine (β- and α-adrenoceptor agonists, respectively) to reserpine-treated milked snakes promoted the widening of the rough endoplasmic reticulum and restored venom production, but only phenylephrine restored the development of the Golgi apparatus and the formation of many secretory vesicles.
These results provide the first evidence that the sympathetic nervous system plays an important role in venom production and secretion in the venom glands of Bothrops jararaca. Understanding the importance of noradrenergic stimulation in venom production may provide new insights for research into the treatment of snakebites.
Reliability Of Continuous Tracer Infusion For Measuring Glucose Turnover Rate In Rainbow Trout
Authors: Haman François , Powell Mark , Weber Jean-Michel 
Published: April 2021

ABSTRACT
Glucose plays a fundamental role in mammalian energetics but its contribution as a metabolic fuel is not well established for fish; the accurate in vivo measurement of glucose flux is essential to determine the importance of this substrate in the energy budget of teleosts. Therefore, the goal of the present study was to verify the reliability of the continuous tracer infusion method for estimating glucose turnover rate in rainbow trout Oncorhynchus mykiss. Our secondary goals were to determine whether glucose flux can be estimated more accurately from plasma or from whole-blood samples, and to obtain an estimate of renal glucose production. Continuous infusions of [6-3H]glucose were performed in hepatectomized and intact animals. In some hepatectomized individuals, liver glucose production was replaced by a pump infusing unlabelled glucose at a known rate. Renal glucose production was measured in hepatectomized fish where liver glucose production was not replaced, and it averaged 1.1±0.1 µmol kg−1 min−1 (mean ± S.E.M., N=5). Results show that glucose turnover rate is quantified accurately by continuous tracer infusion and that glucose flux can be estimated equally well from plasma (error of −0.7±4.9 %) and from whole-blood (error of −5.7±2.9 %) samples (means ± S.E.M., N=7). This study provides the first experimental validation of continuous tracer infusion in fish, and shows that this method could become a powerful tool to investigate hormonal regulation of glucose metabolism in live teleosts.
Coupling H+ Transport And Atp Synthesis In F1Fo-Atp Synthases: Glimpses Of Interacting Parts In A Dynamic Molecular Machine
Authors: Fillingame Robert H. 
Published: April 2021

ABSTRACT
Reversible, F1Fo-type ATPases (also termed F-ATP synthases) catalyze the synthesis of ATP during oxidative phosphorylation. In animal cells, the enzyme traverses the inner mitochondrial membrane and uses the energy of an H+ electrochemical gradient, generated by electron transport, in coupling H+ translocation to ATP formation. Closely related enzymes are found in the plasma membrane of bacteria such as Escherichia coli, where the enzymes function reversibly depending upon nutritional circumstance. The F1Fo-type enzymes are more distantly related to a second family of H+-translocating ATPases, the vacuolar-type or V-ATPases. Recent structural information has provided important hints as to how these enzymes couple H+ transport to the chemical work of ATP synthesis. The simplest F1Fo-type enzymes, e.g. as in E. coli, are composed of eight types of subunits in an unusual stoichiometry of α3β3γδε (F1) and a1b2c12 (Fo). F1 extends from the membrane, with the α and β subunits alternating around a central subunit γ. ATP synthesis occurs alternately in different β subunits, the cooperative tight binding of ADP+Pi at one catalytic site being coupled to ATP release at a second. The differences in binding affinities appear to be caused by rotation of the γ subunit in the center of the α3β3 hexamer. The γ subunit traverses a 4.5 nm stalk connecting the catalytic subunits to the membrane-traversing Fo sector. Subunit c is the H+-translocating subunit of Fo. Protonation/deprotonation of Asp61 in the center of the membrane is coupled to structural changes in an extramembranous loop of subunit c which interacts with both the γ and ε subunits. Subunits γ and ε appear to move from one subunit c to another as ATP is synthesized. The torque of such movement is proposed to cause the rotation of γ within the α3β3 complex. Four protons are translocated for each ATP synthesized. The movement of γ and ε therefore probably involves a unit of four c subunits. The organization of subunits in Fo remains a mystery; it will have to be understood if we are to understand the mechanism of torque generation.
Regulation of proton-translocating V-ATPases
Authors: Merzendorfer Hans , Gräf Ralph , Huss Markus , Harvey William R. , Wieczorek Helmut 
Published: April 2021

ABSTRACT
Vacuolar-type ATPases (V-ATPases) are proton-translocating enzymes that occur in the endomembranes of all eukaryotes and in the plasma membranes of many eukaryotes. They are multisubunit, heteromeric proteins composed of two structural domains, a peripheral, catalytic V1 domain and a membrane-spanning Vo domain. Both the multitude of locations and the heteromultimeric structure make it likely that the expression and the activity of V-ATPases are regulated in various ways. Regulation of gene expression encompasses control of transcription as well as control at the post-transcriptional level. Regulation of enzyme activity encompasses many diverse mechanisms such as disassembly/reassembly of V1 and Vo domains, oxidation of SH groups, control by activator and inhibitor proteins or by small signalling molecules, and sorting of the holoenzyme or its subunits to target membranes.
Regulation of Na+/Glucose Cotransporters
Authors: Wright Ernest M. , Hirsch Jochen R. , Loo Donald D. F. , Zampighi Guido A. 
Published: April 2021

ABSTRACT
Na+/glucose cotransporters (SGLTs) are expressed in the small intestine and the proximal renal tubule, where they play a central role in the absorption of glucose and galactose from food and the reabsorption of glucose from the glomerular filtrate. The regulation of intestinal sugar absorption occurs over two distinct time scales, one over days and the other over minutes. This review focuses on the mechanisms involved in the shorter-term regulation. Recent studies of the mouse intestine in vitro demonstrated that Na+/glucose cotransport is increased two- to eightfold within minutes by the application of forskolin, an agent that increases intracellular cyclic AMP levels. Here we explore how cyclic AMP may upregulate Na+/glucose cotransport. Our strategy was to express cloned SGLT1s in Xenopus laevis oocytes and then use electrophysiological methods to measure (i) the kinetics of Na+/glucose cotransport, (ii) the number of cotransporters in the plasma membrane, and (iii) the net rate of exo- and endocytosis before and after activation of protein kinases. To evaluate the role of cotransporter phosphorylation, we have examined the effect of protein kinase activation on various SGLT1 isoforms and other cotransporters. In oocytes expressing rabbit SGLT1, the activation of protein kinase A (PKA) increased the maximum rate of Na+/glucose cotransport by 30 %, and the activation of protein kinase C (PKC) decreased the maximum rate of transport by 60 %. Changes in maximum transport rates were accompanied by proportional changes in the number of cotransporters in the plasma membrane and by changes in the area of the membrane. We conclude that PKA and PKC regulate rabbit SGLT1 activity by modulating the number of cotransporters in the plasma membrane and that this occurs through regulation of exocytosis and endocytosis. Given the size of intracellular transport vesicles containing SGLT1, 100–120 nm in diameter, and the density of cotransporters in these vesicles, 10–20 per vesicle, we estimate that the net rate of SGLT1 vesicle exocytosis is about 10 000 s−1 and that this rate increases 100-fold after activation of PKA. The effect of PKA is independent of the presence or absence of consensus sites for phosphorylation on SGLT1. Surprisingly, the effects of PKA or PKC depend critically on the sequence of the cotransporter being expressed in the oocyte, e.g. activation of PKC inhibited rabbit and rat SGLT1, but stimulated human SGLT1. This dependency suggests that the regulation of vesicle trafficking by protein kinases depends upon the structure of the cotransporter expressed in the oocyte. Similar considerations apply to other classes of cotransporters, such as the neurotransmitter and dipeptide cotransporters. Our working hypothesis is that the regulation of cotransporter expression by protein kinases occurs largely by regulated exo- and endocytosis, and that the effect of the protein kinases is indirect and determined by critical domains in the cotransporter.
Possible involvement of somatolactin in the regulation of plasma bicarbonate for the compensation of acidosis in rainbow trout
Authors: Kakizawa Sho , Ishimatsu Atsushi , Takeda Tatsusuke , Kaneko Toyoji , Hirano Tetsuya 
Published: April 2021

ABSTRACT
Somatolactin is a putative pituitary hormone of the growth hormone/prolactin family in fish. Its function is still unknown. The effects of environmental hypercapnia and hypoxia, acid (HCl) infusion and exhaustive exercise on plasma somatolactin levels were examined in the chronically cannulated rainbow trout to study the possible physiological roles of somatolactin. Respiratory acidosis induced by hypercapnia (2 % CO2) did not affect plasma somatolactin level. In contrast, metabolic acidosis induced by acid infusion and exercise increased plasma somatolactin level. Blood pH was depressed to a similar extent by both types of acidosis, whereas plasma [HCO3−] was elevated by respiratory acidosis but reduced by metabolic acidosis. A moderate hypoxia (water 9.3 kPa) affected neither acid–base status nor plasma somatolactin level. A more severe hypoxia (water 6.1 kPa) resulted in metabolic acidosis accompanied by an apparent rise in plasma somatolactin level, although the difference in somatolactin level from the control value was not statistically significant. Somatolactin immunoneutralization retarded recovery of plasma [HCO3−] following acid infusion. These results indicate that somatolactin is involved in the retention of HCO3− during metabolic acidosis but not in the active accumulation of HCO3− for acid–base compensation of respiratory acidosis in rainbow trout Oncorhynchus mykiss.
Feeding mechanism and functional morphology of the jaws of the lemon shark Negaprion brevirostris (Chondrichthyes, Carcharhinidae)
Authors: Motta Philip J. , Tricas Timothy C. , Hueter Robert E. , Summers Adam P. 
Published: April 2021

ABSTRACT
This study tests the hypothesis that preparatory, expansive, compressive and recovery phases of biting behavior known for aquatically feeding anamniotes are conserved among extant elasmobranch fishes. The feeding mechanism of the lemon shark Negaprion brevirostris is examined by anatomical dissection, electromyography and high-speed video analysis. Three types of feeding events are differentiated during feeding: (1) food ingestion primarily by ram feeding; (2) food manipulation; and (3) hydraulic transport of the food by suction. All feeding events are composed of the expansive, compressive and recovery phases common to aquatically feeding teleost fishes, salamanders and turtles. A preparatory phase is occasionally observed during ingestion bites, and there is no fast opening phase characteristic of some aquatically feeding vertebrates. During the compressive phase, palatoquadrate protrusion accounts for 26 % of the gape distance during jaw closure and is concurrent with muscle activity in the dorsal and ventral preorbitalis and the levator palatoquadrati. Hydraulic transport events are shorter in duration than ram ingestion bites. Prey ingestion, manipulation and hydraulic transport events are all found to have a common series of kinematic and motor components. Individual sharks are capable of varying the duration and to a lesser extent the onset of muscle activity and, consequently, can vary their biting behavior. We propose a model for the feeding mechanism in carcharhinid sharks, including upper jaw protrusion. This study represents the first electromyographic and kinematic analysis of the feeding mechanism and behavior of an elasmobranch.
Seasonal variation in uptake of short-chain neutral amino acid by red blood cells and hepatocytes in trout (Salmo trutta)
Authors: Gallardo M. A. , Canals P. , Albi J. L. , Pesquero J. , Sanchez J. 
Published: April 2021

ABSTRACT
The present study shows that the capacity of trout (Salmo trutta) red blood cells (RBCs) and freshly isolated hepatocytes to take up short-chain neutral amino acids changes according to a seasonal pattern. Maximal amino acid uptake rates in RBCs were obtained in winter and spring, while minima were seen in summer and autumn. In contrast, the maximal rates for the freshly isolated hepatocytes were obtained in autumn and winter, and the minima were seen in spring and summer.
In addition, by studying the uptake of glycine, evidence was found that the activities of the amino acids carriers ASC, asc and Gly in RBCs varied according to a seasonal rhythm. The activity of the ASC and asc systems changed in parallel with the global uptake of amino acids.
Moreover, the RBC:plasma concentration ratio for certain substrates of these carriers (alanine, serine and glycine) varied accordingly. In contrast, the activity of the Gly system was modified inversely with respect to the overall amino acid uptake.
The activity of the ASC system in freshly isolated hepatocytes was also seasonally modified, reaching a maximum in autumn, shortly before the reproductive period.