bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fluid secretion by isolated malpighian tubules of Drosophila melanogaster Meig.: effects of organic anions, quinacrine and a diuretic factor found in the secreted fluid
Authors: Riegel J. A. , Farndale R. W. , Maddrell S. H. P. 
Published: April 2021

ABSTRACT
Para-aminohippuric acid (PAH, 0.2 and 1 mmol l−1) had no effect on the basal fluid secretion rate (FSR) of isolated Malpighian tubules of Drosophila melanogaster Meig. and did not affect stimulation of the FSR induced by adenosine 3′,5′ -monophosphate (cAMP). Phenol Red (phenolsulphonphthalein, PSP; 0.5 and 1 mmol l−1) slowed the FSR and abolished stimulation of the FSR by cAMP. Diodrast (1 mmol l−1) slightly, but significantly, reduced the FSR and greatly reduced the stimulation of the FSR normally provoked by cAMP and by the 3′,5′-monophosphates of guanosine (cGMP), inosine (cIMP) and uridine (cUMP). However, stimulation of the FSR by the 3′,5′ -monophosphate of cytidine (cCMP) was little affected by diodrast. Probenecid (0.2 or 1 mmol l−1) consistently stimulated the FSR, on average by approximately 25 %, but did not markedly inhibit the subsequent stimulation of the FSR by cAMP, cGMP or cIMP. However, the FSR of tubules stimulated by cGMP was temporarily lowered by probenecid. Quinacrine (0.1 mmol l−1) slowed basal FSR by an average of approximately 30 %, but subsequent stimulation of the FSR by cAMP was not noticeably affected. Both 0.1 mmol l−1 cAMP and 1 mmol l−1 probenecid stimulated adenylate cyclase activity in extracts of Malpighian tubules, but cIMP, cGMP, cUMP and diodrast were without effect in this regard. Uptake of radioactivity from a solution containing 500 nmol l−1 [3H]cAMP and 9.5 μmol l−1 cAMP was reduced by more than 90 % by 1 mmol l−1 PSP, by approximately 40 % by 0.2 mmol l−1 probenecid, by 36 % by 1 mmol l−1 diodrast and by 30 % by 1 mmol l−1 PAH. Neither 0.01 mmol l−1 ouabain nor 0.1 mmol l−1 quinacrine affected the uptake of [3H]cAMP by the Malpighian tubules. Fluid secreted by isolated Malpighian tubules of Drosophila melanogaster contains a factor that stimulated the FSR on average by approximately 50 %. The presence in the secreted fluid of cGMP at a concentration of 8.3 μmol l−1 did not explain the stimulatory effect on FSR.
These results support the existence of a carrier-mediated uptake of cyclic nucleotides into the Malpighian tubules of Drosophila melanogaster, possibly involving a multispecific transporter.
Osmoregulation in Drosophila melanogaster selected for urea tolerance
Authors: Pierce Valerie A. , Mueller Laurence D. , Gibbs Allen G. 
Published: April 2021

ABSTRACT
Animals may adapt to hyperosmolar environments by either osmoregulating or osmoconforming. Osmoconforming animals generally accumulate organic osmolytes including sugars, amino acids or, in a few cases, urea. In the latter case, they also accumulate ‘urea-counteracting’ solutes to mitigate the toxic effects of urea. We examined the osmoregulatory adaptation of Drosophila melanogaster larvae selected to live in 300 mmol l−1 urea. Larvae are strong osmoregulators in environments with high NaCl or sucrose levels, but have increased hemolymph osmolarity on urea food. The increase in osmolarity on urea food is smaller in the selected larvae relative to unselected control larvae, and their respective hemolymph urea concentrations can account for the observed increases in total osmolarity. No other hemolymph components appear to act as urea-counteractants. Urea is calculated to be in equilibrium across body compartments in both selected and control larvae, indicating that the selected larvae are not sequestering it to lower their hemolymph osmolarity. The major physiological adaptation to urea does not appear to involve increased tolerance or improved osmoregulation per se, but rather mechanisms (e.g. metabolism, decreased uptake or increased excretion) that reduce overall urea levels and the consequent toxicity.
Voltage-dependent ionic currents in the ventromedial eclosion hormone neurons of Manduca sexta
Authors: Hewes Randall S. 
Published: April 2021

ABSTRACT
The ventromedial cells (VM cells) of the moth Manduca sexta belong to a peptide hormone signaling hierarchy that directs an episodic and stereotyped behavior pattern, ecdysis. The VM cells respond to declining ecdysteroid titers at the end of the final larval molt with a transcription-dependent decrease in spike threshold and the abrupt release of the previously stockpiled neuropeptide, eclosion hormone (EH). This report describes whole-cell patch-clamp recordings of acutely isolated VM cell somata made to identify membrane currents that may underlie the increase in VM cell excitability during EH release and that may contribute to abrupt peptide release. There were at least three voltage-and time-dependent conductances in the VM cells. The inward current was carried exclusively by a voltage-dependent inward Ca2+ current (ICa), and the outward currents were a combination of a Ca2+-dependent outward K+ current (IK(Ca)) and a transient, voltage-dependent outward K+ current, the A current (IA). In current-clamp recordings, the currents present in the acutely isolated somata were sufficient to generate membrane properties similar to those observed in the VM cells in situ. This study represents the first step toward characterization of the mechanisms underlying the abrupt release of EH stores from the VM cells preceding ecdysis.
Lipid restructuring does not contribute to elevated activities of Na+/K+-ATPase in basolateral membranes from the gill of seawater-acclimated eel (Anguilla rostrata)
Authors: Crockett Elizabeth L. 
Published: April 2021

ABSTRACT
In teleost fishes, increases in gill Na+/K+-ATPase activity accompanying the transition from fresh water to sea water may be attributed to changes in either the numbers of enzyme molecules present or to turnover number (kcat). The sensitivity of Na+/K+-ATPase to its chemical/physical environment in the membrane makes it plausible that modulation of enzyme activity may be driven, in part, by changes in membrane properties. In the current study, I test the hypothesis that lipid compositional changes (restructuring) contribute to the modulation of gill Na+/K+-ATPase activity. An enriched preparation of basolateral membranes was prepared from the gills of freshwater- and seawater-acclimated American eel (Anguilla rostrata). Phospholipid class distribution, fatty acyl chain compositions and cholesterol contents were determined. Phosphatidylcholine, the most abundant phospholipid present in gill basolateral membranes, makes up more than 60 % of the total phospholipid content in both freshwater- and seawater-acclimated animals. The contents of other phospholipids and major fatty acyl chains are also similar for the two acclimation groups. Cholesterol/phospholipid molar ratios are 0.28 for freshwater and 0.29 for seawater animals. The similarity between lipid compositions in membranes from freshwater- and seawater-acclimated eels indicates that lipid restructuring is not a mechanism for modulation of gill Na+/K+-ATPase activity in Anguilla rostrata, at least during the acclimation time course used in the present study.
Antibody to H+ V-Atpase subunit E colocalizes with portasomes in alkaline larval midgut of a freshwater mosquito (Aedes aegypti L.)
Authors: Zhuang Zhengpeng , Linser Paul J. , Harvey William R. 
Published: April 2021

ABSTRACT
The pH profile, gross structure, ultrastructure and immunolabeling of the mosquito (Aedes aegypti) larval midgut are described as a first step in analyzing the role of plasma membrane H+ V-ATPase in the alkalization of the gut, nutrient uptake and ionic regulation. Binding of an antibody to H+ V-ATPase subunit E colocalizes with ‘portasomes’ (approximately 10 nm in diameter), which are thought to correspond to the V1 part of the H+ V-ATPase. In gastric caeca (pH 8), both antibody-binding sites and portasomes are located apically; in the anterior midgut (pH 10–11), they are located basally; and in the posterior midgut (pH≈8) they are again located apically. The hypothesis that the energization of alkalization is mediated by an H+ V-ATPase is supported by the inability of larvae to maintain the high pH after 72 h in 10 μM bafilomycin B1. Confirming earlier reports, the two principal epithelial cell types are designated as ‘columnar’ and ‘cuboidal’ cells. The apical plasma membranes (microvilli) of epithelial cells in the gastric caeca and basal infoldings of anterior midgut are invaded by mitochondria that lie within approximately 20 nm of the portasome-studded plasma membranes.
The colocalization of V-ATPase-immunolabeling sites and portasomes to specific plasma membranes within so-called ‘mitochondria-rich’ cells of gastric caeca and anterior midgut suggests that midgut alkalization in mosquitoes is achieved by molecular mechanisms similar to those that have been described in caterpillars, even though the gross structure of the midgut and the localization of the V-ATPase are dissimilar in the two species. In caterpillars, the high alkalinity is thought to break down dietary tannins, which block nutrient absorption; it may play a similar role in plant-detritus-feeding mosquito larvae. The colocalization of immunolabeling sites and portasomes, together with the presence of long, ‘absorptive-type’ microvilli in the posterior midgut, suggest that the V-ATPase energizes nutrient uptake there.
Contraction parameters, myosin composition and metabolic enzymes of the skeletal muscles of the etruscan shrew Suncus etruscus and of the common european white-toothed shrew Crocidura russula (Insectivora: soricidae)
Authors: Peters Thomas , Kubis Hans Peter , Wetzel Petra , Sender Susanne , Asmussen Gerhard , Fons Roger , Jürgens Klaus D. 
Published: April 2021

ABSTRACT
In the Etruscan shrew, the isometric twitch contraction times of extensor digitorum longus (EDL) and soleus muscles are shorter than in any other mammal, allowing these muscles to contract at outstandingly high contraction frequencies. This species has the highest mass-specific metabolic rate of all mammals and requires fast skeletal muscles not only for locomotion but also for effective heat production and for an extremely high ventilation rate. No differences could be detected in the fibre type pattern, the myosin heavy and light chain composition, or in the activity of the metabolic enzymes lactate dehydrogenase and citrate synthase of the two limb muscles, the EDL and the soleus, which in larger mammalian species exhibit distinct differences in contractile proteins and metabolic enzymes. All properties determined in EDL and soleus muscles of Suncus etruscus, as well as in the larger Crocidura russula, are typical for fast-oxidative fibres, and the same holds for several other skeletal muscles including the diaphragm muscle of S. etruscus. Nevertheless, the EDL and soleus muscles showed different mechanical properties in the two shrew species. Relaxation times and, in C. russula, time to peak force are shorter in the EDL than in the soleus muscle. This is in accordance with the time course of the Ca2+ transients in these muscles. Such a result could be due to different parvalbumin concentrations, to a different volume fraction of the sarcoplasmic reticulum in the two muscles or to different Ca2+-ATPase activities. Alternatively, the lower content of cytosolic creatine kinase (CK) in the soleus compared with the EDL muscle could indicate that the observed difference in contraction times between these shrew muscles is due to the CK-controlled activity of their sarcoplasmic reticulum Ca2+-ATPase.
Metamorphosis in the summer flounder Paralichthys dentatus: changes in gill mitochondria-rich cells
Authors: Schreiber Alex M. , Specker Jennifer L. 
Published: April 2021

ABSTRACT
Salinity tolerance changes during larval development and metamorphosis in the summer flounder (Paralichthys dentatus) and other teleosts. The physiological mechanisms responsible for osmoregulation during these early stages of development are not well understood. This study characterized changes in ultrastructure, intracellular membranes and immunoreactive Na+/K+-ATPase of mitochondria-rich cells (MRCs) in the gills of summer flounder during metamorphosis. Gill ultrastructure at the start of metamorphosis revealed only one type of MRC, which had weak reactivity to osmium and lacked a well-defined apical pit. In juveniles, two types of MRCs were observed: light-staining MRCs (LMRCs) with weak reactivity to osmium, and dark-staining MRCs (DMRCs) with strong reactivity to osmium and positioned adjacent to LMRCs. Compared with MRCs at the start of metamorphosis, the mitochondria of juvenile MRCs appeared smaller, with more transverse cristae and electron-dense matrices. Changes in MRCs during metamorphosis were also accompanied by increased immunoreactive Na+/K+-ATPase. These findings suggest that gill MRCs develop during the metamorphosis of summer flounder as the gill takes on an increasingly important osmoregulatory role.
Leptocephalus energetics: metabolism and excretion
Authors: Bishop R. E. , Torres J. J. 
Published: April 2021

ABSTRACT
Leptocephali are the unusual transparent larvae that are typical of eels, bonefish, tarpon and ladyfish. Unlike the larvae of all other fishes, leptocephali may remain in the plankton as larvae for several months before metamorphosing into the juvenile form. During their planktonic phase, leptocephali accumulate energy reserves in the form of glycosaminoglycans, which are then expended to fuel metamorphosis. The leptocephalus developmental strategy is thus fundamentally different from that exhibited in all other fishes in two respects: it is far longer in duration and energy reserves are accumulated.
It was anticipated that the unusual character of leptocephalus development would be reflected in the energy budget of the larva. This study describes the allocation of energy to metabolism and excretion, two important elements of the energy budget. Metabolic rates were measured directly in four species of leptocephali, Paraconger caudilimbatus, Ariosoma balearicum, Gymnothorax saxicola and Ophichthus gomesii, using sealed-jar respirometry at sea. Direct measurements of metabolic rates were corroborated by measuring activities of lactate dehydrogenase and citrate synthase, two key enzymes of intermediary metabolism, in addition to that of Na+/K+-ATPase, a ubiquitous ion pump important in osmotic regulation. Excretion rates were determined by subsampling the sea water used in the respiratory incubations. The entire premetamorphic size range for each species was used in all assays.
Mass-specific oxygen consumption rate, excretion rate and all enzyme activities (y) declined precipitously with increasing mass (M) according to the equation y=aMb, where a is a species-specific constant and −1.74&lt;b&lt;−0.44. In leptocephali, the highly negative slope of the familiar allometric equation describing the relationship between mass-specific metabolic rate and mass, normally between −0.33 and 0, showed that a massive decline in metabolic rate occurs with increasing size. The result suggests that the proportion of actively metabolizing tissue also declines with size, being replaced in large measure by the metabolically inert energy depot, the glycosaminoglycans. Leptocephali can thus grow to a large size with minimal metabolic penalty, which is an unusual and successful developmental strategy.
Artificial Selection For Increased Wheel-Running Activity In House Mice Results In Decreased Body Mass At Maturity
Authors: Swallow John G. , Koteja Pawel , Carter Patrick A. , Garland Theodore 
Published: April 2021

ABSTRACT
To test the hypothesis that body size and activity levels are negatively genetically correlated, we conducted an artificial selection experiment for increased voluntary wheel-running activity in house mice (Mus domesticus). Here, we compare body masses of mice from control and selected lines after 14 generations of selection. In both groups, beginning at weaning and then for 8 weeks, we housed half of the individuals with access to running wheels that were free to rotate and the other half with wheels that were locked to prevent rotation. Mice from selected lines were more active than controls at weaning (21 days) and across the experiment (total revolutions during last week: females 2.5-fold higher, males 2.1-fold higher). At weaning, mice from selected and control lines did not differ significantly in body mass. At 79 days of age, mice from selected lines weighed 13.6 % less than mice from control lines, whereas mice with access to free wheels weighed 4.5 % less than ‘sedentary’ individuals; both effects were statistically significant and additive. Within the free-wheel-access group, individual variation in body mass of males was negatively correlated with amount of wheel-running during the last week (P&lt;0.01); for females, the relationship was also negative but not statistically significant (P&gt;0.40). The narrow-sense genetic correlation between wheel-running and body mass after 8 weeks of wheel access was estimated to be −0.50. A negative genetic correlation could account for the negative relationship between voluntary wheel-running and body mass that has been reported across 13 species of muroid rodents.
Regulation of swimming in the Culex pipiens (Diptera, Culicidae) pupa: kinematics and locomotory trajectories
Authors: Brackenbury John 
Published: April 2021

ABSTRACT
High-speed videography was used to investigate swimming kinematics and locomotory trajectories during escape responses in the pupa of Culex pipiens (Diptera, Culicidae). The pupa can perform straight-line motion despite undergoing backward and forward somersaults through 400 ° at a rate of 20 s−1. For linear motion to occur, the effective stroke of the abdomen must be delivered during the part of each cycle when the body is facing forwards, allowing passive rotation to carry the body round to the correct position for the start of the next half-stroke. On–off motion of the abdomen is regulated by a click mechanism based on stressed integumentary plates which buckle at strategic points in the cycle. The importance of self-inertia as a component in positional regulation was demonstrated by increasing the kinematic viscosity of the medium: this retarded rotation and resulted in somersaulting on the spot. Whereas normally the pupa invariably directs its swimming downwards, reversal of the usual light gradient produced upward paths as well. It is concluded that straight-line motion is generated automatically by the locomotory machine without any need for sensory feedback about body orientation during each cycle, but that swimming direction can be influenced by sensory cues such as light.
Ca2+ uptake in the sarcoplasmic reticulum from the systemic heart of octopod cephalopods
Authors: Altimiras Jordi , Hove-Madsen Leif , Gesser Hans 
Published: April 2021

ABSTRACT
We have measured Ca2+ uptake in crude homogenates of heart tissue, as well as cell shortening and ionic currents in isolated myocytes exposed to caffeine, to characterize Ca2+ uptake in the sarcoplasmic reticulum (SR) of the systemic heart of octopus. The maximal rate of SR Ca2+ uptake in crude homogenates of octopus heart was 43±4 (mean ± S.E.M., N=7), compared with 28±2 nmol min−1 mg−1 protein (N=4) in homogenates of rat heart. The Ca2+-dependency of SR Ca2+ uptake was similar for the two species, with a Ca2+ activity at half-maximal uptake rate (pCa50) of 6.04±0.02 for octopus and 6.02±0.05 for rat. Exposure of isolated myocytes to 10 mmol l−1 caffeine resulted in cell shortening to 53±2 % of the resting cell length and an inward trans-sarcolemmal ionic current. The charge carried by this current was 3.28±0.70 pC pF−1 (mean ± S.E.M., N=5) corresponding to extrusion of 34.0±0.7 amol Ca2+ pF−1 from the cell by Na+/Ca2+ exchange. This is approximately 50 times more than the Ca2+ carried by the Ca2+ current elicited by a 200 ms depolarization from —80 to 0 mV and corresponds to an increase in the total intracellular [Ca2+] of 404±86 μmol l−1 non-mitochondrial volume due to Ca2+ release from the SR. Thus, we find that at 20 °C in the SR both Ca2+ content and Ca2+ uptake rate in the systemic heart of octopus are comparable with or larger than the corresponding values obtained in the rat heart. These results support the argument that the SR may play an important role in the regulation of contraction in the systemic heart of cephalopods.
Ultrastructural and protein analysis of surfactant in the Australian lungfish Neoceratodus forsteri: evidence for conservation of composition for 300 million years
Authors: Power J. H. T. , Doyle I. R. , Davidson K. , Nicholas T. E. 
Published: April 2021

ABSTRACT
The Australian lungfish Neoceratodus forsteri is the most primitive member of the lungfish family, with a surfactant lipid composition similar to the actinopterygiian fishes, which evolved 400 million years ago. We have analysed the proteins associated with surfactant isolated from lung lavage of this species, and used electron microscopy and immunohistochemistry to examine the surfactant structures and the subcellular localisation of these proteins. The epithelial lining of the gas-exchange region of the lungfish lung consists of one basic cell type, which has characteristics of both mammalian alveolar type I and type II cells and may be the common ancestor of both. It has long cytoplasmic plates containing microvilli, large osmiophilic bodies resembling mammalian lamellar bodies and a cytoplasm rich in metabolic organelles. Extracellular structures reminiscent of mammalian surfactant forms, but not including tubular myelin, were observed in the airspaces. Immunochemical analysis of the lungfish surfactant and lung tissue, using antibodies to human SP-A and SP-B, showed a similar staining pattern to human surfactant, indicating that SP-A- and SP-B-like proteins are present. Immunohistochemistry revealed that both SP-A and SP-B reactivity was present in the secretory cell osmiophilic bodies. In conclusion, our results suggest that, despite the great diversity in present day lung structures, a common cellular mechanism may have evolved to overcome fundamental problems associated with air-breathing.
Work-dependent deactivation of a crustacean muscle
Authors: Josephson Robert K. , Stokes Darrell R. 
Published: April 2021

ABSTRACT
Active shortening of respiratory muscle L2B from the crab Carcinus maenas results in contractile deactivation, seen as (1) a decline of force during the course of isovelocity shortening, (2) a reduction in the rate of force redevelopment following shortening, (3) a depression of the level of isometric force reached following shortening, and (4) an accelerated relaxation at the end of stimulation. The degree of deactivation increases with increasing distance of shortening, decreases with increasing shortening velocity, and is approximately linearly related to the work done during shortening. Deactivation lasts many seconds if stimulation is maintained, but is largely although not completely removed if the stimulation is temporarily interrupted so that the force drops towards the resting level. Deactivation for a given distance and velocity of shortening increases with increasing muscle length above the optimum length for force production. Stimulating muscle L2B at suboptimal frequencies gives tetanic contractions that are fully fused but of less than maximal amplitude. The depression of force following shortening, relative to the force during an isometric contraction, is independent of the stimulus frequency used to activate the muscle, indicating that deactivation is not a function of the background level of stimulus-controlled muscle activation upon which it occurs. Deactivation reduces the work required to restretch a muscle after it has shortened, but it also lowers the force and therefore the work done during shortening. The net effect of deactivation on work output over a full shortening/lengthening cycle is unknown.