bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electrophysiology of the In Situ Contractile Vacuole Complex of Paramecium Reveals its Membrane Dynamics and Electrogenic Site During Osmoregulatory Activity
Authors: Tominaga Takashi , Allen Richard D. , Naitoh Yutaka 
Published: April 2021

ABSTRACT
In the freshwater protozoan Paramecium multomicronucleatum, excess cytosolic water, acquired osmotically, is segregated and expelled to the cell exterior through the activity of the contractile vacuole complex. This process keeps the cell volume constant. The electrophysiological parameters of the organelle were measured in situ using a fine-tipped microelectrode inserted into the contractile vacuole, the exocytotic vesicle of the organelle to which the segregated fluid is transported before being expelled to the exterior. The input capacitance decreased markedly immediately before fluid expulsion and regained its previous value when fluid filling resumed after fluid expulsion. This change in the capacitance proved that the contractile vacuole became disconnected from its radial arms, which project from the vacuole, before fluid expulsion occurred and then reconnected with the arms after fluid expulsion. A positive electrical potential was recorded from the contractile vacuole only when it was connected to the radial arms.
This implies that the electrogenic mechanism resides exclusively in the radial arms and supports the idea that the decorated spongiomes, V-type proton-pump-covered terminal tubules of the radial arms that end blindly in the cytosol, are electrogenic. The linear current–voltage relationship of the contractile vacuole membrane also implies that few voltage-activated ion channels are present in the membrane. To explain the movement of water into the contractile vacuole complex, we favour the hypothesis that the potential generated across the decorated spongiome membrane can be used to drive counter-anions from the cytosol into the lumen of the complex. The anions could then act as an osmolite to pull cytosolic water into the lumen of the organelle.
Embryonic Temperature Modulates Muscle Growth Characteristics in Larval and Juvenile Herring
Authors: Johnston Ian A. , Cole Nicholas J. , Abercromby Marguerite , Vieira Vera L. A. 
Published: April 2021

ABSTRACT
The influence of embryonic and larval temperature regime on muscle growth was investigated in Atlantic herring (Clupea harengus L.). Eggs of spring-spawning Clyde herring were incubated at 5 °C, 8 °C or 12 °C until hatching and then reared until after metamorphosis at rising temperatures to simulate a seasonal warming. Metamorphosis to the juvenile stage was complete at 37 mm total length (TL), after an estimated 177 days as a larva at 5 °C, 117 days at 8 °C and 101 days at 12 °C. Growth rate and the development of median fins were retarded in relation to body length at 5 °C compared with 8 °C and 12 °C. Between hatching (at 8–9 mm TL) and 16 mm TL, there was a threefold increase in total muscle cross-sectional area, largely due to the hypertrophy of the embryonic red and white muscle fibres. The recruitment of additional white muscle fibres started at approximately 15 mm TL at all temperatures, and by 37 mm was estimated to be 66 fibres day−1 at 5 °C and 103 fibres day−1 at 8 °C and 12 °C. Peptide mapping studies revealed a change in myosin heavy chain composition in white muscle fibres between 20 and 25 mm TL. Embryonic red muscle fibres expressed fast myosin light chains until 24–28 mm TL at 5 °C and 22 mm TL at 12 °C, and new red fibres were added at the horizontal septum starting at the same body lengths. Following metamorphosis, the total cross-sectional area of muscle was similar at different temperatures, although the number of red and white fibres per myotome was significantly greater at the warmest than at the coldest regime. For example, the mean number of white muscle fibres per myotome in 50 mm TL juveniles was calculated to be 23.4 % higher at 12 °C (12 065) than at 5 °C (9775). In other experiments, spring-spawning (Clyde) and autumn-spawning (Manx) herring were reared at different temperatures until first feeding and then transferred to ambient seawater temperature and fed ad libitum for constant periods. These experiments showed that, for both stocks, the temperature of embryonic development influenced the subsequent rate of muscle fibre recruitment and hypertrophy as well as the density of muscle nuclei. Labelling experiments with 5′-bromo-2-deoxyuridine showed that both the hypertrophy and recruitment of muscle fibres involved a rapidly proliferating population of myogenic precursor cells. The cellular mechanisms underlying the environmental modulation of muscle growth phenotype are discussed.
Seasonal Changes in the Cardiovascular, Respiratory and Metabolic Responses to Temperature and Hypoxia in the Bullfrog Rana Catesbeiana
Authors: Rocha Priscila L. , Branco Luiz G. S. 
Published: April 2021

ABSTRACT
We assessed seasonal variations in the effects of temperature on hypoxia-induced alterations in the bullfrog Rana catesbeiana by measuring the heart rate, arterial blood pressure, breathing frequency, metabolic rate, blood gas levels, acid–base status and plasma glucose concentration. Regardless of the season, decreased body temperature was accompanied by a reduction in heart and breathing frequencies. Lower temperatures caused a significant decrease in arterial blood pressure during all four seasons. Hypoxia-induced changes in breathing frequency were proportional to body temperature and were more pronounced during winter, less so during spring and autumn and even smaller during summer. Season had no effect on the relationship between hypoxia and heart rate. At any temperature tested, the rate of oxygen consumption had a tendency to be highest during summer and lowest during winter, but the difference was significant only at 35 °C. The and pH values showed no significant change during the year, but was almost twice as high during winter than in summer and spring, indicating increased plasma bicarbonate levels. Lower temperatures were accompanied by decreased plasma glucose levels, and this effect was greater during summer and smaller during autumn. Hypoxia-induced hyperglycaemia was influenced by temperature and season. During autumn and winter, plasma glucose level remained elevated regardless of temperature, probably to avoid dehydration and/or freezing. In winter, the bullfrog may be exposed not only to low temperatures but also to hypoxia. These animals show temperature-dependent responses that may be beneficial since at low body temperatures the set-points of most physiological responses to hypoxia are reduced, regardless of the season.
Nitric oxide and cyclic GMP modulate photoreceptor cell responses in the visual system of the locust
Authors: Schmachtenberg Oliver , Bicker Gerd 
Published: April 2021

ABSTRACT
Nitric oxide (NO) is a membrane-permeant messenger molecule which activates the cyclic GMP (cGMP)-synthesizing enzyme soluble guanylyl cyclase. Using cytochemical techniques, we recently reported NO-induced cGMP immunoreactivity in the photoreceptor cells of the compound eye of the locust Schistocerca gregaria and also detected NADPH diaphorase staining, a marker of NO synthase, in a subset of the monopolar cells of the lamina. By recording the corneal electroretinogram (ERG), we found that the application of neurochemicals that raise NO/cGMP levels in the optic lobe increased the ERG amplitude, whereas the experimental reduction of NO levels caused a decrease in the response to light. An increase in the light response was also found in intracellular recordings after application of a NO donor, suggesting that the NO-induced changes in the ERG are not caused by changes in the resistive isolation of the retina. Our cytochemical and electrophysiological data are both consistent with the hypothesis that NO synthesized in monopolar cells is a retrograde messenger to the presynaptic photoreceptor neurones.
Chloride channels in the eel intestine
Authors: Bicho A. , Ferreira H. Gil , Ferreira K. Gil 
Published: April 2021

ABSTRACT
Patches of freshly isolated epithelial cells from eel Anguilla anguilla intestine bathed by the same solution on both sides in the cell-attached configuration had conductances of 57.0±1.8 pS (for positive voltages) and 13.3±0.7 pS (for negative voltages) (means ± S.E.M., N=25). Electrical activity was spontaneous in the cell-attached configuration, but was frequently lost after excision. In inside-out patches, channel activity was restored by strong hyperpolarization (−150 mV for 5 s) or depolarization (+150 mV for 5 s). Channel activity was inhibited by the Cl− transport blocker DIDS (1 mmol l−1).
The membrane potential measured using the nystatin slow whole-cell technique in primary cultured eel intestine epithelial cells was −35.4±1.0 mV (N=14), similar to the expected equilibrium potential for Cl− (−38.2 mV). Removal of Cl− from the bath or application of DIDS caused 16 mV and 6–7 mV depolarizing shifts in reversal potential, respectively. In one experiment, DIDS also induced a reduction in cell conductance from 0. 011±0.014 to 0.002±0.005 nS. The addition of 0.5 mmol l−1 8-(4-chlorophenylthio)-adenosine 3′,5′-cyclic monophosphate (a membrane-permeable analogue of cyclic AMP) to the bath caused an increase in conductance without affecting the reversal potential.
Load–Elongation Characteristics Of in vivo Human Tendon and Aponeurosis
Authors: Maganaris Constantinos N. , Paul John P. 
Published: April 2021

ABSTRACT
In the present study, we measured the in vivo load–elongation characteristics of the human tibialis anterior tendon and its central aponeurosis. Measurements were taken in five men using dynamometry, muscle electrical stimulation and ultrasonography. Percutaneous tetanic stimulation of the muscle at successive voltages corresponding to 20, 40, 60, 80 and 100 % of maximum isometric dorsiflexion moment was applied. During electrical stimulation, we recorded the displacements of the tibialis anterior tendon origin and its aponeurosis proximal end using B-mode ultrasonography. Aponeurosis displacement was calculated by subtracting tendon displacement from the displacement of the aponeurosis proximal end. Tendon and aponeurosis displacements increased curvilinearly from 1.3 to 4 mm and from 3.7 to 12 mm, respectively, as a function of dorsiflexion load. Scaling of the displacements recorded to the resting lengths (measured over the skin) yielded strain values that increased curvilinearly with load, from 0.8 to 2.5 % in the tendon and from 2.1 to 7 % in the aponeurosis. Tendon strain was smaller by between 61 and 64 % compared with aponeurosis strain at any given contraction level. These findings are in line with reports from in vitro isolated material testing and have important implications for muscle modelling.
Effects Of Complex Radiative And Convective Environments On The Thermal Biology Of The White-Crowned Sparrow (Zonotrichia Leucophrys Gambelii)
Authors: Wolf Blair O. , Wooden K. Mark , Walsberg Glenn E. 
Published: April 2021

ABSTRACT
The energy budgets of small endotherms are profoundly affected by characteristics of the physical environment such as wind speed, air temperature and solar radiation. Among these, solar radiation represents a potentially very large heat load to small animals and may have an important influence on their thermoregulatory metabolism and heat balance. In this investigation, we examined the interactive effects of wind speed and irradiance on body temperature, thermoregulatory metabolism and heat balance in the white-crowned sparrow (Zonotrichia leucophrys gambelii). We measured changes in metabolic heat production by exposing birds to different wind speeds (0.25, 0.5, 1.0 and 2.0 m s−1) and irradiance combinations (&lt;3W m−2 and 936±11 W m−2; mean ± S.D.) at an air temperature of 10 °C.
Body temperature was not affected by wind speed, but was significantly higher in animals not exposed to simulated solar radiation compared with those exposed at most wind speeds. In the absence of solar radiation, metabolic heat production was strongly affected by wind speed and increased by 30 % from 122 to 159 W m−2 as wind speed increased from 0.25 to 2.0 m s−1. Metabolic heat production was even more strongly influenced by wind speed in the presence of simulated solar radiation and increased by 51 % from 94 to 142 W m−2 as wind speed increased from 0.25 to 2.0 m s−1. Solar heat gain was negatively correlated with wind speed and declined from
28 to 12 W m−2 as wind speed increased from 0.25 to 2.0m s−1 and, at its maximum, equaled 11 % of the radiation intercepted by the animal. The overall thermal impact of the various wind speed and irradiance combinations on the animal’s heat balance was examined for each treatment. Under cold conditions, with no solar radiation present, an increase in wind speed from 0.25 to 2.0m s−1 was equivalent to a decrease in chamber air temperature of 12.7 °C. With simulated solar radiation present, a similar increase in wind speed was equivalent to a decrease in chamber air temperature of 16 °C. Overall, shifting environmental conditions from a wind speed of 0.25 m s−1 and irradiance of 936 W m−2 to a wind speed of 2.0m s−1 with no short-wave radiation present was equivalent to decreasing chamber air temperature by approximately 20 °C.
The sensitivity to changes in the convective environment, combined with the complex effects of changes in irradiance levels revealed by re-analyzing data published previously, significantly complicates the task of estimating the heat balance of animals in nature.
Spray Mechanism of the Most Primitive Bombardier Beetle (Metrius Contractus)
Authors: Eisner Thomas , Aneshansley Daniel J. , Eisner Maria , Attygalle Athula B. , Alsop David W. , Meinwald Jerrold 
Published: April 2021

ABSTRACT
The bombardier beetle Metrius contractus discharges its defensive secretion as a froth that clings to its body. When attacked from the rear, it allows the froth to build up over the gland openings near the abdominal tip; when attacked from the front, it conveys the secretion forwards along special elytral tracks. M. contractus has two-chambered defensive glands typical of bombardier beetles, and its secretion, like that of other bombardiers, is quinonoid and hot. Its frothing mechanism, however, is unique for bombardiers and possibly illustrative of the ancestral glandular discharge mechanism of these beetles. M. contractus, thus, could be the least derived of extant bombardiers.
Ocellar Pigmentation and Phototaxis in the Nematode Mermis Nigrescens: Changes During Development
Authors: Burr A. H. Jay , Wagar Donna , Sidhu Parmjit 
Published: April 2021

ABSTRACT
After 1 or 2 years of dormancy in the soil, Mermis nigrescens females emerge to lay eggs on vegetation where their grasshopper hosts are likely to feed. Females collected at this life stage exhibit a strong positive phototaxis and have a tubular region of pigmentation near the anterior tip consisting of concentrated oxyhaemoglobin. A previous investigation of the scanning motion of the ‘head’ and orientation of the ‘neck’ has implicated the shadowing of a photoreceptor inside the tube as the mechanism for identifying the direction of light during phototaxis. Here, we describe the development of the pigment in young adult females and investigate phototaxis in early developmental stages that lack the pigment. The orientation of the neck to a horizontal 420 nm stimulus (intensity 1013 photons s−1 cm−2) was measured for unpigmented fourth-stage larvae and immature adult females as well as mature females with pigmented ocelli. The orientation of the larvae and immature adults was weakly negative, whereas that of the mature adults was strongly positive. Head and neck movements were otherwise the same in the three stages. Thus, the pigmentation appears to be required for positive phototaxis, and the results provide further support for the shadowing role of ocellar haemoglobin.
Energy Metabolism of the Virginia Opossum During Fasting and Exercise
Authors: Weber Jean-Michel , O’connor Timothy 
Published: April 2021

ABSTRACT
Rates of oxygen consumption and CO2 production were measured in Virginia opossums (Didelphis virginiana) during fasting and prolonged exercise to quantify changes in total energy expenditure and oxidative fuel selection. We hypothesized that fasting would cause metabolic depression and a progressive shift towards lipid utilization to spare alternative substrates. It was also predicted that prolonged exercise would cause the same relative changes in fuel preference as fasting, but on a compressed time scale. The results show that hypometabolism is not used by the Virginia opossum to cope with food deprivation. However, a rapid exhaustion of limited carbohydrate reserves is prevented through a sixfold reduction in the percentage contribution of carbohydrates to total energy expenditure made possible by an increase in lipid utilization. No protein sparing is observed in this species. Prolonged low-intensity exercise elicits a potent mobilization of lipids that allows maximal running time to be extended by delaying the depletion of limited carbohydrate reserves. We conclude that fasting and prolonged low-intensity exercise cause similar changes in the relative use of lipids and carbohydrates, but on a different time scale, supporting the idea that endurance exercise is the metabolic equivalent of ‘accelerated fasting’. The absence of metabolic depression and protein sparing during fasting shows that such physiological strategies have not been necessary for the rapid range expansion towards the North recently shown by this species.
The Effect Of Metabolic Depression on Proton Leak Rate in Mitochondria From Hibernating Frogs
Authors: St-Pierre J. , Brand M.D. , Boutilier R.G. 
Published: April 2021

ABSTRACT
Futile cycling of protons across the mitochondrial inner membrane accounts for 20 % or more of the total standard metabolic rate of a rat. Approximately 15 % of this total is due to proton leakage inside the skeletal muscle alone. This study examined whether the rate of proton leak is down-regulated as a part of a coordinated response to energy conservation during metabolic depression in cold-submerged frogs. We compared the proton leak rate of skeletal muscle mitochondria isolated from frogs at different stages of hibernation (control, 1 month and 4 months of submergence in normoxia and hypoxia). The kinetics of mitochondrial proton leak rate was unaltered throughout normoxic and hypoxic submergence. The state 4 respiration rates did not differ between control animals and frogs hibernating in normoxia. In contrast, the state 4 respiration rates obtained from frogs submerged in hypoxic water for 4 months were half those of control animals. This 50 % reduction in respiration rate in hypoxic hibernation was due to a reduction in electron transport chain activity and consequent decrease in mitochondrial membrane potential. We conclude that proton leak rate is reduced during metabolic depression as a secondary result of a decrease in electron transport chain activity, but that the proton conductance is unchanged. In addition, we show that the rate of proton leakage and the activity of the electron transport chain are lower in frogs than in rats, strengthening the observation that mitochondria from ectotherms have a lower proton conductance than mitochondria from endotherms.
Effects of Fish Size and Temperature On Weakfish Disturbance Calls: Implications For the Mechanism of Sound Generation
Authors: Connaughton M. A. , Taylor M. H. , Fine M. L. 
Published: April 2021

ABSTRACT
To categorize variation in disturbance calls of the weakfish Cynoscion regalis and to understand their generation, we recorded sounds produced by different-sized fish, and by similar-sized fish at different temperatures, as well as muscle electromyograms. Single, simultaneous twitches of the bilateral sonic muscles produce a single sound pulse consisting of a two-to three-cycle acoustic waveform. Typical disturbance calls at 18 °C consist of trains of 2–15 pulses with a sound pressure level (SPL) of 74 dB re 20 μPa at 10 cm, a peak frequency of 540 Hz, a repetition rate of 20 Hz and a pulse duration of 3.5 ms. The pulse duration suggests an incredibly short twitch time. Sound pressure level (SPL) and pulse duration increase and dominant frequency decreases in larger fish, whereas SPL, repetition rate and dominant frequency increase and pulse duration decreases with increasing temperature. The dominant frequency is inversely related to pulse duration and appears to be determined by the duration of muscle contraction. We suggest that the lower dominant frequency of larger fish is caused by a longer pulse (=longer muscle twitch) and not by the lower resonant frequency of a larger swimbladder.
Allometric Relationships Between Embryonic Heart Rate and Fresh Egg Mass in Birds
Authors: Tazawa Hiroshi , Pearson James T. , Komoro Takashi , Ar Amos 
Published: April 2021

ABSTRACT
Previously, we have measured daily changes (developmental patterns) in embryonic heart rate (fH) in altricial and semi-altricial (ASA) birds (range of mean fresh egg mass approximately 1–20 g), semi-precocial seabirds (egg mass approximately 38–288 g) and precocial birds (egg mass approximately 6–1400 g). An allometric relationship between embryonic fH at 80 % of incubation duration (ID) and fresh egg mass (M) has been derived for six species of precocial bird (fH at 80 % ID=429M−0.118). In the present study, additional measurements of embryonic fH in three ASA species, the barn owl Tyto alba, the cattle egret Bubulcus ibis and the lanner falcon Falco biarmicus, were made to extend the egg mass range (20–41 g), and the allometric relationships of embryonic fH for these ASA birds and the precocial and semi-precocial (PSP) groups were investigated from published data. The developmental patterns of embryonic fH in three relatively large ASA species did not show a significant increase prior to the pipping period, unlike those in small ASA birds, but tended to be constant, with a subsequent increase during pipping. The allometric relationship derived for ASA birds was Fh at 80 % ID=371M−0.121 (r=−0.846, P&lt;0.001, N=20) and that for PSP birds was fH at 80 % ID=433M−0.121 (r=−0.963, P&lt;0.001, N=13). The slopes were parallel, but fH of ASA embryos was low compared with that of PSP embryos with the same egg mass. In ASA birds, embyronic fH was maximal during the pipping (perinatal) period, and the maximum fH (fHmax) was significantly related to fresh egg mass: fHmax=440M−0.127 (r=−0.840, P&lt;0.001, N=20). The allometric relationships for fH at 80 % ID in PSP and fHmax in ASA embryos were statistically identical. Accordingly, embryonic fH at 80 % ID in PSP birds and fHmax during pipping in ASA birds can be expressed by a single allometric equation: fH=437M−0.123 (r=−0.948, P&lt;0.001, N=33).