bluuebunny/crossref_metadata_2025 huggingface dataset:
Allatostatin Decreases Stomatogastric Neuromuscular Transmission in the Crab Cancer Borealis
Authors: Jorge-Rivera Juan Carlos , Marder Eve
Published: April 2021

The effects of insect allatostatins (ASTs) 1–4 were studied on the stomach musculature of the crab Cancer borealis. Of these, Diploptera-allatostatin 3 (D-AST-3) was the most effective. D-AST-3 (10−6 mol l−1) reduced the amplitude of nerve-evoked contractions, excitatory junctional potentials and excitatory junctional currents at both cholinergic and glutamatergic neuromuscular junctions. Muscle fiber responses to ionophoretic applications of both acetylcholine and glutamate were reduced by the peptide, but D-AST-3 produced no apparent change in the input resistance of the muscle fiber. D-AST-3 reduced the amplitude of muscle contractures evoked by both acetylcholine and glutamate, but had no effect on contractures induced by a high [K+]. These data suggest that D-AST-3 decreases the postsynaptic actions of both neurally released acetylcholine and glutamate. Because an AST-like peptide is found in peripheral sensory neurons that innervate stomatogastric muscles and in the pericardial organs, we suggest that an AST-like peptide may play a role in controlling the gain of the excitatory neuromuscular junctions in the stomach.
Modulation of Electrical Activity by 5-Hydroxytryptamine in Crayfish Neurosecretory Cells
Authors: Sáenz Francisco , García Ubaldo , Aréchiga Hugo
Published: April 2021

The effect of 5-hydroxyptryptamine (5-HT) was tested in a population of X organ neurosecretory cells in the eyestalk of the crayfish Procambarus clarkii. Tests were conducted both in situ and on isolated neurones kept in culture.

The application of 5-HT induced action potentials in silent cells. In spontaneously active neurones, 5-HT increased the firing rate and either induced firing or enhanced bursting activity. The effect of 5-HT was dose-dependent within the range 1–100 μmol l−1 in cells of the intact organ. The effect persisted for 20–30 min after 5-HT had been removed from the bathing solution. Successive applications of 5-HT onto the same neurone reduced responsiveness, suggesting that desensitization had occurred. The effects of 5-HT were blocked by prior incubation with the 5-HT antagonist methysergide.

In X organ cells whose axons and branches in the neuropile had been severed, 5-HT induced a depolarisation associated with a slow inward current. In X organ neurones isolated from the eyestalk and kept in culture, 5-HT was capable of evoking bursts of action potentials and elicited a slow inward current. This effect was also blocked by methysergide (10−4 mol l–1).

These results suggest a direct modulatory effect of 5-HT on the pattern of electrical activity in the X organ cells.
In Vivo Performance of Trunk Muscles in Tree Frogs During Calling
Authors: Girgenrath M. , Marsh R. L.
Published: April 2021

We used high-speed video and electromyography (EMG) to measure in vivo performance of the trunk muscles (external obliques) in two related species of North American gray tree frogs, Hyla versicolor and Hyla chrysoscelis. Both species produce trilled calls with high sound intensity, but the sound pulse frequency within calls in H. chrysoscelis is twice that in H. versicolor. In both species, sound pulse frequency is directly correlated with the active contractions of the trunk muscles. The length trajectory during contraction and relaxation displays a saw-tooth pattern with a longer shortening phase compared with the lengthening phase. The longer time spent shortening may enhance power production, because the shortening phase is the active part of the cycle during which the muscle produces positive work. A similar total strain (approximately 21 % and approximately 19 % in H. versicolor and H. chrysoscelis respectively) is achieved in the first few pulses, and during subsequent pulses the muscle cycles with a reduced pulse strain (approximately 12 % and approximately 7.3 % in H. versicolor and H. chrysoscelis respectively). The higher pulse frequencies of H. chrysoscelis are thus associated with lower pulse strains. The EMG pattern is different in the two species. A single EMG stimulus occurs for each cycle in H. chrysoscelis, but two stimuli per cycle are found in H. versicolor. Indirect evidence suggests that the initial phase of shortening during a pulse is partly due to elastic recoil of the trunk.
Effects of Vagal Stimulation on Swimbladder Blood Flow in the European Eel Anguilla Anguilla
Authors: Schwerte Thorsten , Axelsson Michael , Nilsson Stefan , Pelster Bernd
Published: April 2021

The influence of the vagus nerve on swimbladder blood flow in the European eel (Anguilla anguilla) was characterized by recording the changes in blood flow rate and blood pressure following stimulation of the vagus nerve. After electrical stimulation, blood flow in the swimbladder artery increased from 0.9 ml min−1 to 2.1 ml min−1. Video recordings of small vessels on the caudal side of the rete mirabile revealed an increase in erythrocyte velocity combined with a small vasodilation. This effect could not be blocked by injection of the α-adrenergic antagonist phentolamine, the β-adrenergic antagonist propranolol or the muscarinic cholinoceptor antagonist atropine. In all preparations with a high initial flow rate (>1.9 ml min−1), vagotomy resulted in a marked decrease in blood flow (by approximately 80 %). This effect was not observed in preparations with a low initial swimbladder blood flow. Stimulation of the vagus nerve produced a decrease, and vagotomy produced an increase, in perfusion pressure in blood-perfused swimbladder preparations. Histological studies revealed the presence of a ganglion in the vagus nerve located on the anterior part of the resorbing section of the swimbladder close to the origin of the ductus pneumaticus, which is probably associated with swimbladder function. These results suggest that swimbladder blood flow, at least to some extent, is under vagal tonic control. The effects do not, however, appear to involve the classical α- and β-adrenergic or muscarinic cholinoceptor functions.
Renal Function and Plasma Levels of Arginine Vasotocin During Free Flight in Pigeons
Authors: Giladi Itamar , Goldstein David L. , Pinshow Berry , Gerstberger Rüdiger
Published: April 2021

We examined urinary water loss and plasma levels of arginine vasotocin (AVT) in free-flying, tippler pigeons trained to fly continuously for up to 5 h. First, we used [3H]polyethyleneglycol ([3H]PEG) as a glomerular filtration marker by implanting an osmotic minipump into each bird. In two flights (10 birds in winter at an ambient temperature of 13–15 °C and seven in summer at 23 °C), we measured pre-flight (hydrated, resting control birds) and post-flight [3H]PEG activity and osmolality in blood and ureteral urine. For comparison, we measured these variables in 10 birds in winter before and after controlled dehydration (24 h at 25 or 30 °C). Second, we measured plasma levels of AVT in 6–8 birds before and immediately after each of three different summer flights. Urine osmolality increased significantly by up to three times the control level in both post-flight and dehydrated pigeons; urine:plasma osmolality ratios did not exceed 2. Compared with controls, glomerular filtration rate (GFR) was significantly lower after flight in summer, but did not change in either post-flight or dehydrated winter pigeons. In winter, mean post-flight urine flow rate (UFR) decreased significantly to less than half the control level, while in summer, post-flight UFR did not differ from control levels. In general, mean filtered water reabsorption increased from 95 % in controls to 98 % in post-flight and dehydrated birds. Plasma levels of AVT increased after flight to between three and eight times the preflight levels. The data from this first study of kidney function during flight are consistent with previous studies of dehydration in birds and exercise in mammals in which both increased and decreased GFR contribute to renal conservation of water.
Migration and Bidirectional Phototaxis in Dictyostelium Discoideum Slugs Lacking the Actin Cross-Linking 120 kDa Gelation Factor
Authors: Wallraff Eva , Wallraff Hans G.
Published: April 2021

Three mutant strains of Dictyostelium discoideum, lacking different actin-binding proteins, were tested for behavioural deficits in the multicellular pseudoplasmodium (slug) stage. Two strains, defective in the production of either α-actinin (an actin cross-linker) or severin (an actin capping and severing protein), did not show changes in slug behaviour. Slugs of the mutant lacking another actin cross-linker, the 120 kDa gelation factor (ABP-120), however, migrated shorter distances in darkness as well as in horizontally directed light. More remarkably, they migrated at an angle of approximately 45 ° to the left or right of the incident light, whereas wild-type slugs migrated on fairly straight paths towards the light. We discuss the hypothesis that this bidirectional oblique-angle phototaxis is due to changes in the optical properties of the pseudoplasmodia. Normally, in wild-type slugs, a lens effect causes stronger stimulation on the side distal to the incident light. We propose that in the mutant the lens quality is reduced, so that at small angles between the slug axis and the rays of light the proximal side is stimulated more intensely. As a result, the intended symmetrical stimulation is achieved at a certain angle to the left or right of the incident light. We assume that the absence of ABP-120 alters the shape of the lens and/or enhances internal light scattering via degradation of intercellular coherence; however, intracellular attenuation of light remains an additional or alternative possibility.
FMRFamide-Like Peptides in the Crayfish (Procambarus Clarkii) Stomatogastric Nervous System: Distribution and Effects on the Pyloric Motor Pattern
Authors: Tierney Ann Jane , Blanck Jennifer , Mercier A. Joffre
Published: April 2021

Whole-mount immunocytochemistry was used to map the location of FMRFamide-like peptides in the crayfish (Procambarus clarkii) stomatogastric nervous system. This system contains the pyloric and gastric mill central pattern generators, which receive modulatory inputs from projection neurons with somata located primarily in other ganglia of the stomatogastric nervous system. Our studies revealed stained somata in the commissural and esophageal ganglia. A pair of stained somata was located in the inferior ventricular nerve, and another pair of somata was located in the stomatogastric nerve where it is joined by the two superior esophageal nerves. The stomatogastric ganglion contained no stained somata, but the neuropil was brightly stained and 2–4 axons projected laterally in small nerves directly from the ganglion. These results indicate that FMRFamide or related peptides may act as neuromodulators in the crayfish stomatogastric nervous system.

To test this hypothesis, we studied the effects of FMRFamide and four related peptides (DF2, NF1, F1 and LMS) on the pyloric motor pattern. DF2, NF1 and F1 all excited certain pyloric cells, especially the lateral pyloric (LP) and ventricular dilator (VD) neurons, and enhanced pyloric cycling frequency in most actively rhythmic preparations. FMRFamide had no detectable effects on pyloric cells, and LMS had inhibitory effects, causing disruption of the pyloric rhythm in actively cycling preparations and reducing tonic activity in non-rhythmic preparations.
The Two Essential Light Chains of Carp Fast Skeletal Myosin, Lc1 and Lc3, are Encoded by Distinct Genes and Change their Molar Ratio Following Temperature Acclimation
Authors: Hirayama Yasushi , Kanoh Satoshi , Nakaya Misako , Watabe Shugo
Published: April 2021

cDNA libraries were constructed from fast skeletal muscles of carp acclimated to 10 and 30 °C for a minimum of 5 weeks and were screened for myosin alkali light chains, LC1 and LC3, using an anti-skipjack LC1 polyclonal antibody. Two types of LC1 cDNA clone were isolated and termed LC1a and LC1b: their nucleotide sequences showed 92 % homology. The ratio of LC1a to LC1b cDNA clones isolated was approximately 3:1, showing no apparent changes following temperature acclimation. The occurrence of the two isoforms was further confirmed by N-terminal amino acid sequencing of purified LC1. No isoform was, however, detected for LC3, while homology in the overlapping region between LC1a and LC3 cDNAs was only 65 % even after the most probable alignment.

Southern blot analyses probed with cDNA clones specific to LC1a and LC3 showed different hybridization patterns from each other, demonstrating that carp LC1 and LC3 are encoded by different genes. These results are in marked contrast to those from higher vertebrates which express LC1 and LC3 from a single gene by alternative RNA transcription and two modes of splicing. Northern blot analysis showed that the ratios of LC3/LC1 mRNAs were significantly higher (3.93) in 30 °C-acclimated than in 10 °C-acclimated (3.10) carp.
Odorant Intensity as a Determinant for Olfactory Conditioning in Honeybees: Roles in Discrimination, Overshadowing and Memory Consolidation
Authors: Pelz Corinna , Gerber Bertram , Menzel Randolf
Published: April 2021

Stimulus intensity is an important determinant for perception, learning and behaviour. We studied the effects of odorant concentration on classical conditioning involving odorants and odorant-mechanosensory compounds using the proboscis-extension reflex in the honeybee.

Our results show that high concentrations of odorant (a) support better discrimination in a feature-positive task using rewarded odorant-mechanosensory compounds versus unrewarded mechanosensory stimuli, (b) have a stronger capacity to overshadow learning of a simultaneously trained mechanosensory stimulus, and (c) induce better memory consolidation. Furthermore, honeybees were trained discriminatively to two different concentrations of one odorant. Honeybees are not able to solve this task when presented with rewarded low versus unrewarded high concentrations.

Taken together, our results suggest that high concentrations of odorant support stronger associations (are more ‘salient’) than low concentrations. Our results, however, do not indicate that honeybees can treat two different concentrations of one odorant as qualitatively different stimuli. These findings fill a gap in what is known about honeybee olfactory learning and are a first step in relating behaviour to recent advances in the physiological analysis of coding for odorant concentration in honeybees.
Thermally Induced Changes in Intracellular pH and Modulators of Phosphofructokinase in Trout White Muscle
Authors: Lehoux Eric A. , Guderley Helga E.
Published: April 2021

The intracellular pH (pHi) and the concentrations of lactate and selected modulators of phosphofructokinase (PFK; EC 2.7.1.11) were measured in white epaxial muscle of 15 °C-acclimated rainbow trout (Oncorhynchus mykiss) maintained at 8, 15 or 22 °C for 48 h and sampled at rest and after 10 min of exhaustive exercise. The lactate accumulation resulting from exercise was 13 % smaller at 22 °C than at 8 and 15 °C. The estimated duration of burst performance was shorter at cold than at warm temperatures, whereas the average rate of lactate accumulation during burst performance was higher at 8 °C than at 15 and 22 °C. pHi rose when temperature decreased, but less than predicted by the imidazole alphastat hypothesis of Reeves. The effects of temperature on the pre-exercise concentrations of PFK modulators [adenylates, fructose 6-phosphate (F6P) and fructose 1,6-bisphosphate (FBP)] were generally negligible. In exhausted trout, adenylate concentrations were almost unaffected by temperature. In contrast, post-exercise FBP and F6P concentrations were significantly higher at low than at high temperatures. We interpret the response of F6P to temperature as an indication that the covariation of pHi and temperature is insufficient to prevent a cold-enhancement of PFK inhibition. Since F6P is a potent activator of PFK, we conclude that, in trout white muscle, thermally induced changes in F6P concentration probably help buffer the effects of temperature change on PFK activity.
Possible Mediation of G-Proteins in Cold-Sensory Transduction in Paramecium Multimicronucleatum
Authors: Nakaoka Yasuo , Tanaka Tohru , Kuriu Toshihiko , Murata Tomohisa
Published: April 2021

The possible involvement of G-proteins in cold-sensory transduction was examined using voltage-clamped Paramecium multimicronucleatum into which non-hydrolyzable guanosine nucleotide analogues had been applied intracellularly. Guanosine-5′-O-3-thiotriphosphate, guanosine-5′-O-2-thiodiphosphate and aluminium fluoride all reduced the transient inward current in response to cooling, suggesting the possibility that G-proteins mediate cold-sensory transduction. Internal application of a Ca2+ chelator, EGTA, also reduced the current response. In addition to their effect on reducing the cold-sensory response, application of these chemicals modulated both the resting potential and the membrane conductance. Possible correlations between G-protein activity and the regulation of intracellular Ca2+ levels are discussed.
Local Interneurons Define Functionally Distinct Regions Within Lobster Olfactory Glomeruli
Authors: Wachowiak M. , Diebel C. E. , Ache B. W.
Published: April 2021

Whole-cell recording coupled with biocytin injection revealed four types of interneurons intrinsic to the olfactory lobe (OL) of the spiny lobster Panulirus argus. Each type of neuron had a distinct pattern of arborization within the three anatomically defined regions of OL glomeruli (cap, subcap and base). Type I interneurons innervated all three regions, while types II, III and IV branched only in the cap, subcap and base, respectively. Type I interneurons responded to electrical stimulation of the antennular (olfactory) nerve with a burst of 1–20 action potentials and a 1–10 s depolarization. Type II (cap) interneurons responded to the same input with a burst of 1–3 action potentials followed by a shorter hyperpolarization. Type III (subcap) interneurons responded with a burst of 1–6 action potentials followed by a delayed, 0.5–4 s depolarization. Type IV (base) interneurons responded with a brief depolarization or a burst of 1–3 action potentials followed by a 1 s hyperpolarization. The regionalized arborization and the different response properties of the type II, III and IV interneurons strongly imply that lobster olfactory glomeruli contain functionally distinct regions, a feature that should be useful in understanding the multiple synaptic pathways involved in processing olfactory input.
Recovery after Contraction of White Muscle Fibres from the Dogfish Scyliorhinus Canicula
Authors: Curtin N. A. , Kushmerick M. J. , Wiseman R. W. , Woledge R. C.
Published: April 2021

Recovery after contraction of white muscle fibres of dogfish was investigated using 31P-NMR and measurements of heat production. The muscle fibres were stimulated to perform either a single isometric tetanus or a series of brief isometric tetani; the NMR measurements showed that approximately half of the phosphocreatine (PCr) was used. The period of activity was followed by a recovery period without stimulation.

Both NMR and heat measurements agreed in showing that recovery was very slow, requiring at least 60 min for PCr resynthesis and for the production of recovery heat. The NMR results showed that changes in intracellular pH and in the concentrations of PCr and intracellular phosphate (Pi) had very similar time courses. Intracellular pH moved in the alkaline direction during the period of activity and then returned monotonically during recovery. The non-phosphate buffer power was 13.0±3.1 mmol l−1 intracellular water per pH unit (N=4, mean ± S.E.M.).

The results are consistent with the view that oxidative processes resynthesize PCr during recovery, which is slow because of the low mitochondrial content of these muscle fibres.
Central Nervous Processing of Sex Pheromones in Two Strains of the European Corn Borer Ostrinia Nubilalis (Lepidoptera: Pyralidae)
Authors: Anton Sylvia , Löfstedt Christer , Hansson Bill S.
Published: April 2021

Antennal lobe neurones were investigated in the pyralid moth Ostrinia nubilalis using intracellular recording and staining techniques. Response characteristics of antennal lobe neurones from males in the so-called E and Z strains, in F1 hybrids and in parental backcrosses were studied. The antennal lobe of a male O. nubilalis comprises approximately 30 ordinary glomeruli and three enlarged glomeruli making up the macroglomerular complex (MGC). Receptor neurones enter the antennal lobe via the antennal nerve and arborize in single glomeruli. Intracellularly stained, pheromone-responding projection neurones in both parental strains arborized in different glomeruli within the MGC, irrespective of their response characteristics. Neurones were grouped according to their specificity to single pheromone components and to pheromone blends. Component-specific, blend-specific and generalist neurones were found. Specificity only occurred at low stimulus concentrations and disappeared as concentrations increased. Although all neuronal types were present in both pheromone strains and crossings, differences in abundance and sensitivity were found. In the parental strains, neurones responding to the major pheromone component and to the respective strain-specific blend were more abundant than neurones responding to the minor component and the blend produced by the other strain. Neurones investigated in Z×E hybrids responded similarly to those of E-strain males, whereas neurones in EZ×Z paternal backcrosses responded similarly to those of Z males. In the hybrids and paternal backcrosses, hybrid-blend-specific neurones were present that were not found in parental-strain males.
Stability Of Nucleoside Triphosphate Levels In The Red Cells Of The Snake Thamnophis Elegans
Authors: Ingermann Rolf L. , Bencic David C. , Herman Jay K.
Published: April 2021

Nucleated red cells in the nonpregnant garter snake (Thamnophis elegans) contain relatively high concentrations of nucleoside triphosphate (NTP), largely in the form of ATP, which is found at concentrations of approximately 10 mmol l− 1 relative to cell volume and 15 mmol l− 1 relative to cell water. During pregnancy, levels of NTP in adult red cells rise by approximately 50 % concomitant with an increase in blood progesterone level. The stability of the NTP pool within these red cells was assessed by maintaining cells in vitro at 20 °C, without exogenous nutrients, and in the presence and absence of the metabolic inhibitors iodoacetate and/or cyanide. After 96 h, NTP levels in adult red cells not exposed to the inhibitors had decreased by only approximately 10 %, while in the presence of both inhibitors NTP levels had fallen by less than 50 %. Red cell NTP levels were not affected by acute exposure to high concentrations of progesterone either in vivo or in vitro. NTP levels were much more labile when the cells were maintained in vitro at either low or high pH. Maintenance of red cells at pH 6.0 for 24 h resulted in a decrease in NTP levels of approximately 50 % and at pH 10.0 the levels fell by approximately 80 %, while buffers containing only ATP caused no detectable degradation. Incubation at low or high pH promoted some cell swelling; however, the magnitude of the decreases in intracellular NTP concentration prompted by these pH levels could not be mimicked by incubation of red cells in hypotonic buffer. Total nonspecific ATPase activity at pH 6.0 was approximately 55 % greater than that at pH 7.4, while at pH 10.0 it was approximately 6 % of that at pH 7.4. The pH-dependent decrease in intracellular NTP levels cannot, therefore, be due to stimulation of ATPase activity, at least not at high pH. Overall, the data are consistent with the hypothesis that an appreciable portion of the NTP within these cells is compartmentalized in a stable, but pH-sensitive, pool sequestered from intracellular ATP-hydrolyzing processes.
Locomotion in the Abalone Haliotis Kamtschatkana: Pedal Morphology and Cost of Transport
Authors: Donovan Deborah A. , Carefoot Thomas H.
Published: April 2021

Morphological analyses of pedal sole area and pedal waves were conducted for a range of speeds and body sizes in the abalone Haliotis kamtschatkana. The pedal sole of resting abalone increased in size disproportionately with animal volume (slope of log10-transformed data, b=0.83; expected slope for isometry, b0=0.67) and length (b=2.51; b0=2.0). Pedal wave frequency increased linearly with speed, confirming that abalone increase speed by increasing the velocity of pedal waves. Total area of the pedal sole decreased by 2.1 % for each shell length per minute increase in speed. Likewise, the area of the foot incorporated into pedal waves increased by 1.8 % for each shell length per minute increase in speed. Together, these changes translated into a 50 % decrease in the pedal sole area in contact with the substratum at a maximum escape speed of 15 shell lengths min−1, relative to the pedal sole at rest. The amount of mucus secreted by resting animals during adhesion to the substratum increased isometrically with foot area (slope of log10-transformed data, b=1.08). The amount of mucus secreted during locomotion did not vary with speed, but was less than the amount needed for adhesion. We suggest that these morphological and physiological changes reduce the energy expenditure during locomotion. Cost of transport was investigated for a range of speeds and abalone sizes. The rate of oxygen consumption (in μl O2 g−1 h−1) increased linearly with increasing absolute speed v (in cm min−1): =40.1+0.58v−0.15m (r2=0.35, P=0.04), where m is body mass (in g). Minimum cost of transport, calculated from the slope of absolute speed on , was 20.3 J kg−1 m−1. Total cost of transport (COTT) and net cost of transport (COTN) were high at low speeds and decreased as speed increased, to minima of 86.0 J kg−1 m−1 and 29.7 J kg−1 m−1, respectively, at speeds measured in the respirometer. Log10-transformation of both cost of transport and speed data yielded linear relationships with the following regression equations: log10COTT=3.35−0.90log10v−0.21log10m (r2=0.89; P<0.006) and log10COTN=2.29−0.69log10v−0.09log10m (r2=0.48; P<0.006), respectively.
Power Output From a Flight Muscle of the Bumblebee Bombus Terrestris : I. Some Features of the Dorso-Ventral Flight Muscle
Authors: Josephson Robert K. , Ellington C. P.
Published: April 2021

Isometric contractions from the asynchronous dorso-ventral flight muscle of the bumblebee Bombus terrestris were slow and rather weak. The twitch duration (onset to 50 % relaxation) was approximately 300 ms at 30 °C and 170 ms at 40 °C. The maximum tetanic tension was approximately 40 kN m−2; the ratio of twitch force to tetanic force was approximately 0.2. The unstimulated muscle was quite resistant to stretch, with a low-frequency stiffness of 730 kN m−2 at muscle lengths close to that of the muscle in vivo. The length–tension curve for active tetanic tension (that is the increase in tension above the passive level during stimulation) was very narrow, with a half-width equal to only 17 % of the optimal length. The muscle strain during tethered flight was approximately 2 % peak-to-peak, occasionally reaching 3 %. Strain amplitude increased with wing stroke frequency. The thoracic vibration frequency of escape buzzing, during which the wings are not extended but are folded over the abdomen, was approximately twice that of tethered flight but the muscle strain was similar to that of flight.
Honeybee Flight Muscle Phosphoglucose Isomerase: Matching Enzyme Capacities to Flux Requirements at a Near-Equilibrium Reaction
Authors: Staples James F. , Suarez Raul K.
Published: April 2021

In honeybee flight muscle, there are close matches between physiological flux rates and the maximal activities (Vmax; determined using crude homogenates) of key enzymes catalyzing non-equilibrium reactions in carbohydrate oxidation. In contrast, phosphoglucose isomerase (PGI), which catalyzes a reaction believed to be close to equilibrium, occurs at Vmax values greatly in excess of glycolytic flux rates. In this study, we measure the Vmax of flight muscle PGI, the kinetic parameters of the purified enzyme, the apparent equilibrium constants for the reaction and the tissue concentrations of substrate and product. Using the Haldane equation, we estimate that the forward flux capacity (Vf) for PGI required to achieve physiological glycolytic flux rates is between 800 and 1070 units ml−1 cell water, approximately 45–60 % of the empirically measured Vmax of 1770 units ml−1 cell water at optimal pH (8.0) and low ionic strength (no added KCl). When measured at physiological pH (7.0) and ionic strength (120 mmol l−1 KCl) with saturating levels of substrate, PGI activity is 1130 units ml−1 cell water, a value close to the calculated Vf. These results reveal a very close match between predicted and measured PGI flux capacities, and support the concept of an economical design of muscle metabolism in systems working at very high metabolic rates.
Contraction Kinetics of Red Muscle in Scup: Mechanism for Variation in Relaxation Rate Along the Length of the Fish
Authors: Swank Douglas M. , Zhang Guixin , Rome Lawrence C.
Published: April 2021

We studied possible mechanisms for the twofold difference in red muscle relaxation times between the posterior (207.2 ms) and anterior (98.4 ms) musculature of scup Stenotomus chrysops, which has been shown to have a large effect on power generation during swimming. This difference was not due to contamination of the anterior bundles with faster fiber types, as histological examination showed that all bundles contained more than 98.9 % red fibers. Further, maximum velocities of shortening (Vmax) at 20 °C were nearly identical, 5.37 ML s−1 (where ML is muscle length) for the anterior musculature and 5.47 ML s−1 for the posterior musculature, suggesting that the difference in relaxation times was not due to a difference in the crossbridge detachment rates associated with different myosin isoforms. The possibility of differences in the Ca2+ pumping rate influencing relaxation rate was explored using cyclopiazonic acid (CPA), a sarcoplasmic reticulum (SR) Ca2+-ATPase inhibitor. The concentration of CPA could be adjusted to slow the relaxation rate of an anterior muscle to that of a posterior muscle. However, SDS gels showed no difference in the intensity of SR Ca2+-ATPase protein bands between muscle positions. These results suggest that differences in the Ca2+ pumping could account for the observed difference in relaxation rate, but do not support the simplest hypothesis that the difference in relaxation rates is due to differences in numbers of Ca2+ pumps. Other possible mechanisms for this difference are explored.
Release of Atrial Natriuretic Factor Prohormone Peptides 1-30, 31-67 And 99-126 From Freshwater- and Seawater-Acclimated Perfused Trout (Oncorhynchus Mykiss) Hearts
Authors: Cousins K. L. , Farrell A. P. , Sweeting R. M. , Vesely D. L. , Keen J. E.
Published: April 2021

Atrial natriuretic factor (ANF), a 28-amino-acid peptide hormone produced in the heart, circulates in both freshwater and seawater rainbow trout. In mammals, two other peptide hormones, proANF 1-30 and proANF 31-67, derived from the same 126-amino-acid prohormone as ANF (amino acids 99–126), circulate and have natriuretic and diuretic properties. It has never been determined whether these peptides circulate in fish. The present investigation was designed to determine (1) whether proANF 1-30 and/or proANF 31-67 circulate in perfused hearts from freshwater- and seawater-acclimated rainbow trout (Oncorhynchus mykiss) in situ, and (2) if they do, to determine whether increasing the filling pressure of the heart causes their release in trout as it does in mammals. High-performance gel-permeation chromatography of fish plasma revealed that both proANF 1-30 and 31-67 circulate in freshwater- and seawater-acclimated trout plasma at threefold higher concentrations than does ANF. The basal rates of release of ANF and proANF 1-30 and 31-67 were similar in both freshwater and seawater trout, with the rate of release of proANF 1-30 being 10 times higher and that of proANF 31-67 20 times higher than that of ANF. When the filling pressure was increased to the peak of the Starling curve (Q̇max), the rate of release of ANF and proANFs 1-30 and 31-67 increased fivefold for each peptide in the freshwater trout, while in seawater trout the rates of release increased six-to ninefold. We conclude that proANF 1-30 and 31-67, as well as ANF, circulate in both freshwater-and seawater-acclimated trout and do so at concentrations higher than that of ANF. Increasing the filling pressure to the trout heart was found to cause a similar increase in the release rates for each of these peptides, but the maximal increase was higher in the seawater-acclimated trout, apparently because they showed a larger increase in cardiac output.
Coordination of Respiratory Cycles With Wingbeat Cycles in the Black-Billed Magpie (Pica Pica)
Authors: Boggs D. F. , Seveyka J. J. , Kilgore D. L. , Dial K. P.
Published: April 2021

Magpies fly with a variable pattern of wingstroke, including high-amplitude rapid flaps and low-amplitude slower flaps with interspersed brief glides. This allowed us to test the hypothesis that if phasic coordination between respiratory and wingbeat cycles is important mechanically and energetically, then, as a bird changes its wingbeat cycle, its respiratory cycle should change with it. We also tested the strength of the drive to coordinate respiratory to locomotor cycles by stimulating breathing with 5 % CO2 during flight. We found that magpies (N=5) do shorten their breath cycle time when they shorten their wingbeat cycle time and prolong their breath cycle time when they glide. When the coordination ratio of wingbeat cycles to breaths is 3:1, the pattern of phasic coordination ensures two upstrokes per inspiration and two downstrokes per expiration. Upstroke tends to coincide with the transition into inspiration or with early inspiration and late inspiration. Downstroke tends to coincide with the transition into expiration or with early expiration and late expiration. When magpies switch from a 3:1 ratio to a 2:1 ratio of wingbeat cycles to breaths, they shorten inspiratory time to ensure that upstroke occurs through most of inspiration and downstroke corresponds to the transition into expiration. These phasic coordination patterns ensure that the compression of the airsacs during downstroke can provide a net assistance to expiration and that the expansion of the airsacs with upstroke can provide a net assistance to inspiration. The failure of an atmosphere containing 5 % CO2 to disrupt these phasic coordination patterns between respiratory and locomotory cycles suggests that there may be a potent mechanical and energetic benefit to such coordination.
Latitudinal Variation in the Abundance and Oxidative Capacities of Muscle Mitochondria in Perciform Fishes
Authors: Johnston Ian A. , Calvo Jorge , Guderley Helga , Fernandez Daniel , Palmer Lisa
Published: April 2021

The abundance, distribution and oxidative capacities of mitochondria have been investigated in the red pectoral fin adductor muscles of fish (Order Perciformes) that use a predominantly labriform style of swimming. Mediterranean Sea species from the families Labridae, Serranidae, Sparidae and Antarctic Nototheniidae and non-Antarctic Nototheniidae and Channichthyidae were studied. Sub-Antarctic species from the Beagle Channel, Tierra del Fuego, included the pelagic haemoglobin-less icefish (Champsocephalus esox) and the róbalo (Eleginops maclovinus), which occurs as far north as 35°S. In Champsocephalus esox, the mitochondrial volume density of red muscle was 0.51 and mitochondrial cristae surface density (43.9 μm2μm−3) was higher than reported for Antarctic icefishes. In the red-blooded, active pelagic or semi-pelagic species, mitochondrial volume density was within the range 0.27–0.33 regardless of habitat temperature. Amongst less active demersal species, mitochondrial volume density ranged from 0.29–0.33 in polar species to 0.08–0.13 in Mediterranean species. In Antarctic species and Champsocephalus esox, myofibrils occurred in ribbons or clusters one fibril thick entirely surrounded by mitochondria. The volume density of intracellular lipid droplets was not correlated with activity patterns or habitat temperature. In a comparison of Eleginops maclovinus caught in summer (approximately 10°C) and winter (approximately 4°C), mitochondrial volume density did not differ, whereas the surface density of mitochondrial clusters was higher in summer fish. The temperature-dependence of the state 3 respiration rate of isolated mitochondria with pyruvate as substrate was described by a single quadratic relationship for all species, indicating no significant up-regulation of the maximum rate of oxygen uptake per milligram mitochondrial protein in Antarctic species. Our results support the conclusion that increasing the volume and surface density of mitochondrial clusters is the primary mechanism for enhancing the aerobic capacity of muscle in cold-water fish.
Optimal Shortening Velocity (V/Vmax) Of Skeletal Muscle During Cyclical Contractions: Length–Force Effects And Velocity-Dependent Activation And Deactivation
Authors: Askew Graham N. , Marsh Richard L.
Published: April 2021

The force–velocity relationship has frequently been used to predict the shortening velocity that muscles should use to generate maximal net power output. Such predictions ignore other well-characterized intrinsic properties of the muscle, such as the length–force relationship and the kinetics of activation and deactivation (relaxation). We examined the effects of relative shortening velocity on the maximum net power output (over the entire cycle) of mouse soleus muscle, using sawtooth strain trajectories over a range of cycle frequencies. The strain trajectory was varied such that the proportion of the cycle spent shortening was 25, 50 or 75 % of the total cycle duration.

A peak isotonic power output of 167 W kg−1 was obtained at a relative shortening velocity (V/Vmax) of 0.22. Over the range of cyclical contractions studied, the optimal V/Vmax for power production ranged almost fourfold from 0.075 to 0.30, with a maximum net power output of 94 W kg−1. The net power output increased as the proportion of the cycle spent shortening increased. Under conditions where the strain amplitude was high (i.e. low cycle frequencies and strain trajectories where the proportion of time spent shortening was greater than that spent lengthening), the effects of the length–force relationship reduced the optimal V/Vmax below that predicted from the force–velocity curve. At high cycle frequencies and also for strain trajectories with brief shortening periods, higher rates of activation and deactivation with increased strain rate shifted the optimal V/Vmax above that predicted from the force–velocity relationship. Thus, the force–velocity relationship alone does not accurately predict the optimal V/Vmax for maximum power production in muscles that operate over a wide range of conditions (e.g. red muscle of fish).

The change in the rates of activation and deactivation with increasing velocity of stretch and shortening, respectively, made it difficult to model force accurately on the basis of the force–velocity and length–force relationships and isometric activation and deactivation kinetics. The discrepancies between the modelled and measured forces were largest at high cycle frequencies.
Analyses of Cdna and Recombinant Protein for A Potent Vasoactive Protein In Saliva of A Blood-Feeding Black Fly, Simulium Vittatum
Authors: Cupp Mary S. , Ribeiro José M. C. , Champagne Donald E. , Cupp Eddie W.
Published: April 2021

A cDNA was cloned from the salivary glands of a blood-feeding black fly Simulium vittatum. The encoded protein has been given the name Simulium vittatum erythema protein or SVEP, because of its ability to increase blood perfusion in skin capillaries, resulting in the well-characterized erythema of black fly bites. The full-length cDNA contains 548 base pairs which encode 152 amino acid residues of the nascent protein. Post-translational processing produces a mature, secreted protein of 133 residues with a molecular mass of 15.4 kDa. Recombinant SVEP (rSVEP) was produced in a baculovirus expression system and purified by a one-step reversed-phase HPLC procedure. Analyses of physical properties and biological potency demonstrated fidelity of rSVEP to the native protein. Recombinant SVEP relaxed rabbit aorta preparations when preconstricted with 2 μmol l−1 phenylephrine or 25 mmol l−1 K+ but not with 60 mmol l−1 K+. Further, the rSVEP-induced relaxation response of phenylephrine-constricted aorta was inhibited by glibenclamide (10 μmol l−1), suggesting that at least part of its action to relax smooth muscle may result from the opening of ATP-dependent K+ channels. SVEP is a novel salivary-gland-derived vasoactive protein that may be essential for blood feeding by black flies and could potentially enhance transmission of filarial parasites.
Innervation Pattern Of A Pool Of Nine Excitatory Motor Neurons In The Flexor Tibiae Muscle Of A Locust Hind Leg
Authors: Sasaki K. , Burrows M.
Published: April 2021

The flexor tibiae muscle of a locust hind leg consists of 10–11 pairs of fibre bundles in the main body of the muscle and a distal pair of bundles that form the accessory flexor muscle, all of which insert onto a common tendon. It is much smaller than the antagonistic extensor tibiae muscle and yet it is innervated by nine excitatory motor neurons, compared with only two for the extensor. To determine the pattern of innervation within the muscle by individual motor neurons, branches of the nerve (N5B2) that supplies the different muscle bundles were backfilled to reveal somata in the metathoracic ganglion. This showed that different muscle bundles are innervated by different numbers of excitatory motor neurons. Physiological mapping of the innervation was then carried out by intracellular recordings from the somata of flexor motor neurons in the metathoracic ganglion using microelectrodes. Spikes were evoked in these neurons by the injection of current, and matching junctional potentials were sought in fibres throughout the muscle using a second intracellular electrode.

Each motor neuron innervates only a restricted array of muscle fibres and, although some innervate a larger array than others, none innervates fibres throughout the muscle. Some motor neurons innervate only proximal fibres and others only more distal fibres, so that the most proximal and most distal bundles of muscle fibres are innervated by non-overlapping sets of motor neurons. More motor neurons innervate proximal bundles than distal ones, and there are some asymmetries in the number of motor neurons innervating corresponding bundles on either side of the tendon.

Individual motor neurons cause slow, fast or intermediate movements of the tibia, but their patterns of innervation overlap in the different muscle bundles. Furthermore, individual muscle fibres may also be innervated by motor neurons with different properties.
A Genetic Deficiency That Spans the Flightin Gene of Drosophila Melanogaster affects the Ultrastructure and Function of the Flight Muscles
Authors: Vigoreaux Jim O. , Hernandez Carmen , Moore Jeff , Ayer Gretchen , Maughan David
Published: April 2021

We have developed a reverse-genetic approach to study the function of flightin, a unique protein of the flight muscle myofibril of Drosophila melanogaster. We describe the generation and characterization of Df(3L)fln1, a lethal genetic deficiency in the 76BE region of the third chromosome which deletes several genes, including the gene for flightin. We show that heterozygous flies harboring the Df(3L)fln1 mutation exhibit both impaired flight and ultrastructural defects in their flight muscle myofibrils. We found that the mutation does not interfere with assembly of the myofibril but leads to disorganization of peripheral myofilaments in adult myofibrils. Most myofibrils, nevertheless, retain an intact core that represents approximately 80 % of the normal lattice diameter. Mechanical analysis of single skinned flight muscle fibers demonstrates that the mutation has no significant effect on net power output but increases the frequency at which maximum power is delivered to the wings, potentially reducing the overall performance of the flight system. The results suggest that flightin is an indispensable part of the flight muscle contractile mechanism.
Partitioning the Effects of Temperature and Kinematic Viscosity on the C-Start Performance of Adult Fishes
Authors: Johnson T. P. , Cullum A. J. , Bennett A. F.
Published: April 2021

Temperature has been shown to have a significant effect on swimming performance in teleost fish. This thermal dependence has usually been attributed to correlated changes in muscle contractile physiology. However, the physical properties of all materials, including both water and living tissues, are profoundly affected by changes in temperature. In particular, both the kinematic viscosity of water and the flexible body dynamics of the fish (independent of muscle contractile activity) are substantially higher at lower temperatures. In this study, we investigated the extent to which the observed thermal dependence of locomotor performance of fish simply reflects changes in the biophysical properties of the aqueous medium independent of the changing physiology of the animals. C-starts (escape swimming) of adult goldfish (Carassius auratus, length approximately 8 cm) were video-taped (400 frames s−1) at 5 °C and 20 °C in fresh water and at 20 °C in fresh water containing 1.2 % dextran (kinematic viscosity equivalent to that of water at 5 °C). Temperature had a significant positive effect on maximum forward velocity (m s−1), angular velocity (degrees s−1) and total distance moved, but viscosity had no detectable effect on any kinematic parameters at 20 °C. Since viscous forces may have more pronounced effects on smaller fish, C-starts of adult guppies (Poecilia reticulata, length approximately 2 cm) were video-taped in fresh water and in fresh water containing 1.2 % and 3.6 % dextran at 20 °C. Viscosity had a significant effect on kinematic variables only at 3.6 % dextran; at 1.2 % dextran, the effects were marginal. It was concluded that most of the observed thermal dependence of C-starts at temperatures normally experienced by these fish was due to changes in physiological processes as opposed to physical changes in the environment.
The Characterization of Presynaptic Octopamine Receptors Modulating Octopamine Release From an Identified Neurone in the Locust
Authors: Howell Kim M. R. , Evans Peter D.
Published: April 2021

Octopamine release has been demonstrated from the dorsal unpaired median neurone to the locust extensor-tibiae muscle (DUMETi) in response to high-[K+] saline. Here, we provide evidence for the existence of presynaptic inhibitory autoreceptors for octopamine on the DUMETi terminals and report on their pharmacological profile. Octopamine release was initiated by exposure to high-[K+] saline (0.1 mol l−1) and measured using a radioenzyme assay for octopamine. Octopamine receptor antagonists (10−4 mol l−1) potentiated the high-[K+]-mediated release of octopamine with the following rank order of potency: phentolamine = metoclopramide > mianserin = chlorpromazine > cyproheptadine > yohimbine. Octopamine receptor agonists (10−4 mol l−1) inhibited the high-[K+]-mediated release of octopamine with the following rank order of potency: naphazoline > tolazoline > clonidine. Thus, the octopamine autoreceptors on the DUMETi terminals are much closer pharmacologically to the pre-and postsynaptic OCTOPAMINE2 receptors in the locust extensor-tibiae muscle preparation than to the OCTOPAMINE3 receptors from the locust central nervous system. The results suggest that there is likely to be more than one type of insect neuronal octopamine receptor. It is also likely that presynaptic modulation of octopamine release may be confined to octopamine receptors since a wide range of other putative modulatory substances did not produce this effect.