bluuebunny/crossref_metadata_2025 huggingface dataset:
Recycling of the yeast V-SNARE Sec22p involves COPI-proteins and the ER transmembrane proteins Ufe1p and Sec2Op
Authors: Ballensiefen Wolfgang , Ossipov Dmitri , Schmitt Hans Dieter
Published: April 2021

Vesicle-specific SNAP receptors (v-SNAREs) are believed to cycle between consecutive membrane compartments. The v-SNARE Sec22(Sly2)p mediates the targeting of vesicles between endoplasmic reticulum (ER) and early Golgi of Saccharomyces cerevisiae. To analyze factors involved in targeting of Sec22(Sly2)p, an α-factor-tagged Sec22 protein (Sec22-α) was employed. Only on reaching the late Golgi, can α-factor be cleaved from this hybrid protein by Kex2p, a protease localized in this compartment. In wild-type cells Kex2p-cleavage is observed only when Sec22-α is greatly overproduced. Immunofluorescence microscopy and subcellular fractionation studies showed that Sec22-α is returned to the ER from the late Golgi (Kex2p) compartment. When Sec22-α is expressed in wild-type cells at levels comparable to the quantities of endogenous Sec22p, very little of this protein is cleaved by Kex2p. Efficient cleavage, however, occurs in mutants defective in the retrograde transport of different ER-resident proteins indicating that Sec22-α rapidly reaches the late Golgi of these cells. These mutants (sec20-1, sec21-1, sec27-1 and ufe1-1) reveal Golgi structures when stained for Sec22-α and do not show the ER-immunofluorescence observed in wild-type cells. These results show consistently that Sec22p recycles from the Golgi back to the ER and that this recycling involves retrograde COPI vesicles.
Novel features of intermediate filament dynamics revealed by green fluorescent protein chimeras
Authors: Ho Chung-Liang , Martys Jayme L. , Mikhailov Alexei , Gundersen Gregg G. , Liem Ronald K. H.
Published: April 2021

In order to study the dynamic behavior of intermediate filament networks in living cells, we have prepared constructs fusing green fluorescent protein to intermediate filament proteins. Vimentin fused to green fluorescent protein labeled the endogenous intermediate filament network. We generated stable SW13 and NIH3T3 cell lines that express an enhanced green fluorescent protein fused to the N-terminus of full-length vimentin. We were able to observe the dynamic behavior of the intermediate filament network in these cells for periods as long as 4 hours (images acquired every 2 minutes). In both cell lines, the vimentin network constantly moves in a wavy manner. In the NIH3T3 cells, we observed extension of individual vimentin filaments at the edge of the cell. This movement is dependent on microtubules, since the addition of nocodazole stopped the extension of the intermediate filaments. Injection of anti-IFA causes the redistribution or ‘collapse’ of intermediate filaments. We injected anti-IFA antibodies into NIH3T3 cells stably expressing green fluorescent protein fused to vimentin and found that individual intermediate filaments move slowly towards the perinuclear area without obvious disassembly. These results demonstrate that individual intermediate filaments are translocated during the collapse, rather than undergoing disassembly-induced redistribution. Injections of tubulin antibodies disrupt the interactions between intermediate filaments and stable microtubules and cause the collapse of the vimentin network showing that these interactions play an important role in keeping the intermediate filament network extended. The nocodazole inhibition of intermediate filament extension and the anti-IFA microinjection experiments are consistent with a model in which intermediate filaments exhibit an extended distribution when tethered to microtubules, but are translocated to the perinuclear area when these connections are severed.
Actomyosin motor in the merozoite of the malaria parasite, Plasmodium falciparum: implications for red cell invasion
Authors: Pinder J. C. , Fowler R. E. , Dluzewski A. R. , Bannister L. H. , Lavin F. M. , Mitchell G. H. , Wilson R. J. M. , Gratzer W. B.
Published: April 2021

The genome of the malaria parasite, Plasmodium falciparum, contains a myosin gene sequence, which bears a close homology to one of the myosin genes found in another apicomplexan parasite, Toxoplasma gondii. A polyclonal antibody was generated against an expressed polypeptide of molecular mass 27,000, based on part of the deduced sequence of this myosin. The antibody reacted with the cognate antigen and with a component of the total parasite protein on immunoblots, but not with vertebrate striated or smooth muscle myosins. It did, however, recognise two components in the cellular protein of Toxoplasma gondii. The antibody was used to investigate stage-specificity of expression of the myosin (here designated Pf-myo1) in P. falciparum. The results showed that the protein is synthesised in mature schizonts and is present in merozoites, but vanishes after the parasite enters the red cell. Pf-myo1 was found to be largely, though not entirely, associated with the particulate parasite cell fraction and is thus presumably mainly membrane bound.

It was not solubilised by media that would be expected to dissociate actomyosin or myosin filaments, or by non-ionic detergent. Immunofluorescence revealed that in the merozoite and mature schizont Pf-myo1 is predominantly located around the periphery of the cell. Immuno-gold electron microscopy also showed the presence of the myosin around almost the entire parasite periphery, and especially in the region surrounding the apical prominence. Labelling was concentrated under the plasma membrane but was not seen in the apical prominence itself. This suggests that Pf-myo1 is associated with the plasma membrane or with the outer membrane of the subplasmalemmal cisterna, which forms a lining to the plasma membrane, with a gap at the apical prominence. The results lead to a conjectural model of the invasion mechanism.
Expression and characterization of splice variants of PYK2, a focal adhesion kinase-related protein
Authors: Xiong Wen-Cheng , Macklem Marlene , Parsons J. Thomas
Published: April 2021

Focal adhesion kinase and the recently identified proline-rich tyrosine kinase 2 (PYK2), also known as cell adhesion kinase β, related adhesion focal tyrosine kinase or calcium-dependent protein tyrosine kinase, define a new family of non-receptor protein tyrosine kinases. Activation of PYK2 has been implicated in multiple signaling events, including modulation of ion channels, T- and B-cell receptor signaling and cell death. Mechanisms underlying the functional diversity of PYK2 are unclear. Here, we provide evidence for two novel alternatively expressed isoforms of PYK2. One isoform, designated PYK2s (PYK2 splice form), appears to be a splice variant of PYK2 lacking 42 amino acids within the C-terminal domain. A second isoform, referred to as PRNK (PYK2-related non-kinase), appears to be specified by mRNAs that encode only part of the C-terminal domain of PYK2. Northern blot analysis indicates that the unspliced PYK2 is expressed at high levels in the brain and poorly expressed in the spleen, whereas PYK2s and PRNK are expressed in the spleen. In situ hybridization studies of rat brain demonstrate that the unspliced PYK2 is selectively expressed at high levels in hippocampus, cerebral cortex and olfactory bulb, whereas PYK2s and PRNK are expressed at low levels in all regions of rat brain examined. Immunofluorescence analysis of ectopically expressed PRNK protein shows that PRNK, in contrast to full-length PYK2, is localized to focal adhesions by sequences within the focal adhesion targeting domain. In addition, PYK2, but not PRNK, interacts with p130casand Graf. These results imply that PRNK may selectively regulate PYK2 function in certain cells by binding to some but not all PYK2 binding partners, and the functional diversity mediated by PYK2 may be due in part to complex alternative splicing.
Vesicle-associated brain myosin-V can be activated to catalyze actin-based transport
Authors: Evans L. L. , Lee A. J. , Bridgman P. C. , Mooseker M. S.
Published: April 2021

Myosin-V has been linked to actin-based organelle transport by a variety of genetic, biochemical and localization studies. However, it has yet to be determined whether myosin-V functions as an organelle motor. To further investigate this possibility, we conducted a biochemical and functional analysis of organelle-associated brain myosin-V. Using the initial fractionation steps of an established protocol for the purification of brain myosin-V, we isolated a population of brain microsomes that is approx. fivefold enriched for myosin-V, and is similarly enriched for synaptic vesicle proteins. As demonstrated by immunoelectron microscopy, myosin-V associates with 30-40% of the vesicles in this population. Although a majority of myosin-V-associated vesicles also label with the synaptic vesicle marker protein, SV2, less than half of the total SV2-positive vesicles label with myosin-V. The average size of myosin-V/SV2 double-labeled vesicles (90±45 nm) is larger than vesicles that label only with SV2 antibodies (60±30 nm). To determine if these vesicles are capable of actin-based transport, we used an in vitro actin filament motility assay in which vesicles were adsorbed to motility assay substrates. As isolated, the myosin-V-associated vesicle fraction was nonmotile. However, vesicles pre-treated with ice-cold 0.1% Triton X-100 supported actin filament motility at rates comparable to those on purified myosin-V. This dilute detergent treatment did not disrupt vesicle integrity. Furthermore, while this treatment removed over 80% of the total vesicle proteins, myosin-V remained tightly vesicle-associated. Finally, function-blocking antibodies against the myosin-V motor domain completely inhibited motility on these substrates. These studies provide direct evidence that vesicle-associated myosin-V is capable of actin transport, and suggest that the activity of myosin-V may be regulated by proteins or lipids on the vesicle surface.
Compensation of Hypercapnic Acidosis in the Aquatic Blue Crab, Callinectes Sapidus: The Predominance of External Sea Water Over Carapace Carbonate as the Proton Sink
Authors: Cameron James N.
Published: April 2021

Radioactive labelling of the CaCO3 in the crab’s carapace was employed as a tool to study the contribution of the carapace carbonates to acute buffering of acid-base disturbances. Since Ca2+ uptake is extremely rapid during the post-moult period, crabs that moulted in the laboratory were incubated with 45Ca for 5 days immediately following the moult in order thoroughly to load the carapace carbonate pool with radiolabel. After a subsequent 2-week interval for feeding and completion of the post-moult carapace mineralization phase, these 45Ca-loaded crabs were subjected to a 24 h control period and a 24 h hypercapnic period (water equilibrated with 2% CO2 in air) to induce an internal acidosis. Compared with the control period, a compensatory increase in [HCO3−] of 17 mequivl−1 was observed in the blood, along with an apparent H+ excretion to the external sea water of 10-8 mequivkg−1. A statistically significant increase in circulating [Ca2+] and in the specific radioactivity of the blood Ca2+ reached a maximum during the first 3 h of the compensatory phase. By measuring the radioactivity appearing in the water and the blood, and the specific radioactivity of the carapace carbonates, the contribution of the carapace carbonates was calculated to be 7·5% of the total compensatory H+ disposal. The rapid exchange of Ca2+ with the external medium, coupled with physiological regulation of blood [Ca2+] minimized changes in blood [Ca2+]. The total dissolution of carapace CaCO3 was approximately 0·9 mequivkg−1, less than 0·1% of the quantity contained in the shell. The carapace carbonates, therefore, do contribute to acute buffering of hypercapnic acidosis, but their quantitative importance is small, with the gills serving to conduct most of the compensatory exchanges with the environment.
Acceleration Receptors in the Femoral Chordotonal Organ of the Stick Insect, Cuniculina Impigra
Authors: Hofmann T. , Koch U. T.
Published: April 2021

The femoral chordotonal organ of the stick insect Cuniculina impigra was stimulated by moving its apodeme with staircase-like waveforms having independently controllable acceleration and velocity values. Intracellular recordings were made of receptor units in the sensory nerve. Apart from receptors encoding position and velocity (see preceding paper, Hofmann, Koch & Bassler, 1985) specific acceleration receptors and also receptors responding to both the acceleration and the velocity of the stimulus could be distinguished. The pure acceleration receptors fall into two categories: units reacting only to one sign of acceleration (e.g. onset of relaxation and end of elongation) and units reacting to both signs of accelerations. Individual thresholds for each sign of acceleration were measured and analysed. Latencies of the receptors were determined and found to be dependent on the degree of acceleration.

A possible role for the acceleration receptors in an alarm system of the animal is discussed.
Mechanical Properties Of The Octopus Aorta
Authors: Shadwick Roberte. , Gosline John M.
Published: April 2021

The quasi-static mechanical properties of the aorta of Octopus dofleini were investigated using biaxial inflation and uniaxial force-extension tests on vessel segments in vitro. The octopus aorta is a highly compliant and non-linearly elastic structure. The elastic modulus (i.e. the stiffness) measured circumferentially (Ec) and longitudinally (EL) increased markedly with distension of the vessel wall. Ec was always greater than EL, and varied from about 104 to 2x 105 N m−2 between 2 and 5 kPa pressure respectively, the approximate range of resting blood pressure in this species. Increasing vessel wall stiffness is necessary for the aorta to be compliant at low pressure, and at the same time to be protected from ‘blowout’ at high pressure. The non-linear elasticity of the octopus aorta at physiological pressures can be attributed to the properties of the rubber-like elastic fibres which are present in the vessel wall, with little contribution from stiff collagen fibres being required until very high pressures. Dynamic mechanical properties of the aorta were measured by the method of forced oscillations. The dynamic modulus in the circumferential direction increased continuously to almost twice the static value as the frequency was raised from 0·05 to 10Hz. At the same time, the viscous damping, tan δ, increased from 0·11 to 0·27. The resilience of the octopus aorta was close to 70% at the relevant physiological frequencies. We conclude that this vessel is suitably designed to function as an efficient elastic energy storage component in the octopus circulatory system.
Calcium Absorption by the Midgut of the Blowfly, Calliphora Vicina
Authors: Taylor Colin W.
Published: April 2021

The isolated midgut of the adult blowfly, Calliphora vicina, can be maintained under internal perfusion for over 6h, and calcium absorption measured by including 45Ca in the perfusing saline with [3H] inulin as a volume marker. The midgut has a considerable capacity to transport calcium from the lumen (L) to the bathing saline (BS) against its electro-chemical gradient and in the absence of an appreciable net water flux across the gut. Calcium absorption (L-BS) shows saturation kinetics, is totally and reversibly inhibited by metabolic poisons and is accompanied by a negligible backflux (BS-L). It is concluded that the midgut of C. vicina is capable of active calcium transport and that the entire transepithelial calcium flux occurs via a transcellular route. This contrasts with the mammalian duodenum, where absorption occurs via a combination of transcellular and paracellular routes.
Neuronal Mechanisms Underlying Crayfish Steering Behaviour as an Equilibrium Response
Authors: Takahata M. , Yoshino M. , Hisada M.
Published: April 2021

When the crayfish Procambarus is rolled with legs not upon a substratum, uropod opener muscles on the lifted side are activated in co-contraction whereas antagonistic closer muscles on the same side are all relaxed simultaneously. The closers are activated and the openers are relaxed on the lowered side. This reciprocal pattern is also observed in the motor neurone activity: the contraction of opener muscles on the lifted side and closer muscles on the lowered side is caused by an increase in the activity of excitatory motor neurones innervating these muscles, whereas the relaxation of their antagonists on each side is caused by a decrease in the activity of excitatory motor neurones innervating them. Deafferentation by cutting all roots of the terminal ganglion has no significant effect on the steering pattern. The decrease in the excitatory motor neurone activity during steering was found to be due to an increase in the inhibitory input to the motor neurones. During body rolling, the statocyst receptors on the lifted side increase their activity while those on the lowered side decrease it (Takahata & Hisada, 1979). We conclude that the opener motor neurones receive excitation and inhibition respectively from the ipsilateral and the contralateral statocyst, whereas the closer motor neurones receive excitation and inhibition respectively from the contralateral and ipsilateral statocyst. From these results, the connections between the motor neurones and the identified statocyst interneurones were deduced. The normal, bilaterally organized steering pattern of the uropod muscle activity seems to be produced by the statocysts of both sides, whose information is mediated by a bilateral set of interneurones having different connections to individual motor neurones.
Flight Physiology Of Flying Foxes, Pteropus Poliocephalus
Authors: Carpenter Roger E.
Published: April 2021

Oxygen consumption was measured during flight in two flying foxes (Pteropus poliocephalus) at airspeeds of 4–8·6 ms−1. There was good agreement with the measured power input of the only previously measured large bat, and with an allometric equation predicting power input for flying vertebrates. Measurements of respiratory exchange ratios, pulmonary water loss, respiratory frequencies, heart rates and body temperatures of both bats flying at intermediate airspeeds were compared with equivalent measurements on other bats or birds in flight. Despite a high non-evaporative thermal conductance in flight, the P. poliocephalus became severely hyperthermic at ambient temperatures (Ta) above 25°C. The failure to dissipate heat as successfully as flying birds at high Ta is apparently the result of an inability to increase pulmonary ventilation rates, and thus increase rates of evaporative heat loss.

The effect of airspeed on endurance was measured systematically on one bat. Endurance was not limited by energy reserves at all airspeeds, and flight times were significantly greater at the airspeed of minimum power input (Vmp). The endurance of both bats was so reduced at the higher airspeeds that they would not achieve maximum flight range in still air at the velocity where cost of locomotion is lowest. Contrary to a common assumption, flight range would be maximized at the Vmp.
Urine Clearance Rates and Apparent Permeability of Gammarus Duebeni Exposed to Varying Conditions
Authors: Bolt Stephen R. L.
Published: April 2021

Recent investigations indicate that some species of Crustacea have the ability to alter their apparent permeability to water in order to reduce the osmotic stress placed on the animal (Smith, 1967, 1970, 1976; Bolt, 1982; Lockwood, Bolt & Dawson, 1982). The apparent permeability to water of the amphipod Gammarus duebeni (Lilljeborg) varies dramatically when the animal is subjected to varying, salinity regimes (Lockwood, Inman & Courtenay 1973; Dawson, 1982; Bolt, 1982).
Developmental Determination of Central Connections of Sensory Neurones From Wind-Sensitive Hairs in the Locust, Schistocerca Gregaria
Authors: Bacon Jonathan , Anderson Hilary
Published: April 2021

The nervous system of hemimetabolous insects is a favourable preparation in which to study how sensory neurones form particular projections and connections within the CNS. One reason is that the development of the sensory neurones is physically separate from the development of the CNS; sensory neurones are derived from epidermal cells under the cuticle, in contrast to interneurones and motor neurones which are derived from central neuroblasts. In addition, whereas the CNS has an almost full complement of neurones at the end of embryogenesis, neuroblast division having ceased in all but a few brain centres, sensory neurones continue to be generated from their epidermal precursors throughout the postembryonic life of the animal. Therefore transplanting pieces of epidermis during postembryonic development places sensory neurones in altered environments without surgery to the CNS. Furthermore, since sensory neurone development continues within the transplanted epidermis, the influence of these perturbations can be tested on developing as well as regenerating sensory neurones.
Neuromuscular Transmission in the Jellyfish Aglantha Digitale
Authors: Kerfoot P. A. H. , Mackie G. O. , Meech R. W. , Roberts Alan , Singla C. L.
Published: April 2021

In the jellyfish Aglantha digitale escape swimming is mediated by the nearly synchronous activity of eight giant motor axons which make direct synaptic contact with contractile myoepithelial cells on the under-surface of the body wall. The delay in transmission at these synapses was 0·7 ± 0·1 ms (± S.D. ;N= 6) at 12 °C as measured from intracellular records. Transmission depended on the presence of Ca2+ in the bathing medium. It was not blocked by increasing the level of Mg2+ to 127 mmol 1−1. The myoepithelium is a thin sheet of electrically coupled cells and injection of current at one point was found to depolarize the surrounding cells. The potential change declined with distance from the current source as expected for two-dimensional current spread. The two-dimensional space constant (γ) was 770 μm for current flow in the circular direction and 177 μm for radial flow. The internal resistance of the epithelium (178–201 Ωcm) and the membrane time constant (5–10 ms) were direction independent. No propagated epithelial action potentials were observed. Spontaneous miniature synaptic potentials of similar amplitude and rise-time were recorded intracellularly at distances of up to 1 mm from the motor giant axon. Ultrastructural evidence confirms that neuro-myoepithelial synapses also occur away from the giant axons. It is likely that synaptic sites are widespread in the myoepithelium, probably associated with the lateral motor neurones as well as the giant axons. Local stimulation of lateral motor neurones generally produced contraction in distinct fields. We suppose that stimulation of a single motor giant axon excites a whole population of lateral motor neurones and hence a broad area of the myoepithelium.
Identified Muscle Fibres in a Crab. Differences in Facilitation Properties
Authors: Rathmayer W. , Hammelsbeck M.
Published: April 2021

The superficial muscle fibres in the proximal head of the closer muscle in the crab Eriphia belong to four distinct fibre types (I-IV). By stimulating either the ‘slow’ or the ‘fast’ axon, facilitation properties of the EJPs were investigated in eight identifiable muscle fibres which represented the four fibre types. Amount, time course and frequency dependence of facilitation (f) of both ‘slow’ and ‘fast’ EJPs differed characteristically among the fibres studied, but were similar within fibres belonging to the same type. In fibres receiving double excitatory innervation through the ‘slow’ and the ‘fast’ axon (type I and II fibres), the amount of facilitation of ‘fast’ EJPs was smaller than for ‘slow’ EJPs. With the exception of type I fibres, there was an inverse relationship between facilitation and the size of both ‘slow’ and ‘fast’ EJPs. Facilitation increased with frequency and time of stimulation. In type I fibres, facilitation of ‘slow’ EJPs increased with time at low frequencies of stimulation (up to 32 Hz), but decreased at higher frequencies after an initial rise. ‘Fast’ EJPs in type I fibres showed little, if any, facilitation of frequencies below 8 Hz. At frequencies above 8 Hz, they were always depressed (negative values of f). The functional significance of different facilitation properties is discussed with regard to the participation of different muscle fibre types in the mechanical performance of the closer muscle.
Locomotor Activity of the Terrestrial Slug, Limax Maximus: Response to Progressive Dehydration
Authors: Hess Stephen D. , Prior David J.
Published: April 2021

The circadian locomotor rhythm of the terrestrial slug, Umax maximus, was measured with activity wheels during exposure to both humid and drying conditions. Slugs kept in wet wheels (100% RH) remained fully hydrated while those in dry wheels (<30% RH) experienced progressive dehydration. Transfer of slugs from a wet wheel to a dry wheel resulted in an increase in the intensity and duration of their patterned locomotor activity that persisted for 3 days. Once the slugs were returned to wet wheels, their locomotor activity returned to normal.
Plasticity and Proprioception in Insects II. Modes of Reflex Action of the Locust Metathoracic Femoral Chordotonal OrgAn
Authors: Zill Sasha N.
Published: April 2021

Reflex responses of tibial motoneurones were examined during mechanical stimulation of the femoral chordotonal organ, a joint angle receptor of the locust hindleg. Step displacements of the main ligament of the organ, mimicking 10–15° changes in joint angle, produced different patterns of discharge in motoneurones (1) when the leg was resting against a support and (2) when the support was removed to induce active searching movements.

Tibial motoneurones showed resistance reflex responses to oppose the apparent joint movement when the leg rested against a support. Resistance reflexes consisted of constant, short latency excitatory responses followed by discharges that varied in intensity (gain) and degree of tonic coupling. These variations were not due to simple summation with other inputs to motoneurones.

Responses changed during periods of active searching movements. Tibial flexor motoneurones fired phasically in response to apparent joint movement in any direction. Tibial extensor motoneurones were generally inhibited by chordotonal inputs. These reflex changes are not simple reflex ‘reversals’, but represent more complex changes in reflex mode.

Potential functions of each of these reflex modes and the need for plasticity in reflexes of the chordotonal organ are discussed.
Flight Mechanics of A Dragonfly
Authors: Azuma Akira , Azuma Soichi , Watanabe Isao , Furuta Toyohiko
Published: April 2021

The steady slow climbing flight of a dragonfly, Sympetrum frequens, was filmed and analysed. By using the observed data, the mechanical characteristics of the beating wings were carefully analysed by a simple method based on the momentum theory and the blade element theory, and with a numerical method modified from the local circulation method (LCM), which has been developed for analysing the aerodynamic characteristics of rotary wings.

The results of calculations based on the observed data show that the dragonfly performs low speed flight with ordinary airfoil characteristics, instead of adopting an abnormally large lift coefficient. The observed phase advance of the hindwing, Δ δ1 ≃ 80° can be fully explained by the present theoretical calculation. Similarly, the spanwise variation of the airloading and the time variations of the horizontal force, vertical force, pitching moment and torque or power can be definitely estimated within a reasonable range of accuracy in comparison with the flight data. The distribution of loading between the fore and hind pairs of wings is also clarified by the calculations.
Post-Moult Calcification In The Blue Crab (Callinectes Sapidus): Relationships Between Apparent NET H+ Excretion, Calcium And Bicarbonate
Authors: Cameron James N.
Published: April 2021

In the days immediately after moulting, manipulations of external pH, [HCO3−], and [Ca2+] were used to determine the nature of the rapid net Ca2+ influx and attendant apparent net H+ efflux in the blue crab (Callinectes sapidus Rathbun). Both fluxes were strongly inhibited by reductions in external [Ca2+], [HCO3−], or pH. The net Ca2+ influx was reversed at an external concentration of 2·5 mmol 1−1, and both fluxes were reversed by reducing the external [HCO3−] to 0·2 mmol 1−1. The correlation between net Ca2+ flux and apparent net H+ flux was 0·61 (P < 0·01), but the variability and the time course of most experiments indicated that the link was indirect, rather than a direct coupling or cotransport. This conclusion was also borne out by acid-base disturbances that occurred in the low-[Ca2+] treatment. The results are consistent with the hypothesis that inward calcium transport is accompanied by both inward HCO3− transport and outward H+ transport, probably by separate exchanges with ions of like charge such as Na+ and Cl−. Crustecdysone (β-ecdysone) does not appear to be involved in control of these post-moult fluxes and calcification.
Control Of The Orientation Of Cilia By Atp And Divalent Cations In Triton-Glycerol-Extracted Paramecium Caudatum
Authors: Noguchi Munenori , Inoué Hiroshi , Kubo Kazumi
Published: April 2021

The ciliary responses of Paramecium caudatum, extracted in Triton X-100 and glycerol, to the external application of ATP and various divalent cations were examined. Ciliary beating could not be reactivated, but changes in the pointing direction of the cilia (the reorientation response) could be reactivated. The free Ca2+ concentration determined the final orientation of the cilia, which was towards the front when the Ca2+ concentration was above 10−6moll−1, and towards the rear when below 10−7moll−1. The reorientation response was inhibited by vanadate. These results indicate that the mechanism for the reorientation response is separable into two components. One is the movement of cilia to change their pointing direction, which, like normal ciliary beating, is energized by Mg-ATP2–. The other is the determination of the final pointing direction of the cilia, which is Camdependent. Divalent cations can be classified into two groups according to their mode of action on the Ca2+-dependent component. Sr2+ is an agonist and Baz+, Zn2+ and Co2+ are antagonists to Ca2+ for the component.
Activity of Crayfish Abdominal-Positioning Interneurones During Spontaneous and Sensory-Evoked Movements
Authors: Jellies John , Larimer James L.
Published: April 2021

The premotor interneurones that produce coordinated abdominal movements in crayfish (Procambarus) when stimulated directly, are also ‘sensorimotor’. Sets of these interneurones respond in predictable ways to touching the body surface. One set of interneurones (type I) is activated to spiking by touch, while another (type II) receives only subthreshold influences. Several of these interneurones have overlapping receptive fields on the body surface. Touching areas of overlap activates groups of interneurones which discharge at low to moderate frequencies, rather than producing a high-frequency discharge of a single cell. No single positioning interneurone has been identified which is solely responsible for a ‘voluntary’ (spontaneous) motor programme. When active, the positioning interneurones contribute to the production of the behaviour as a member of a constellation of such cells. The results show that this motor system comprises interneurones with sensory as well as motor properties. Although single cells can produce coordinated movements when stimulated at high frequencies, these positioning interneurones appear to function as ‘command elements’ within a large ‘command system’ and not as individual units.
The Influence Of Blood Gas Properties On Gas Tensions And Ph Of Ventral And Dorsal Aortic Blood In Free-SwimmingTuna, Euthynnus Affinis
Authors: Jones David R. , Brill Richard W. , Mense Dennis C.
Published: April 2021

We have developed a technique for capture, anaesthetization, instrumentation and release of tuna and have made the first determinations of blood gas values in dorsal and ventral aortae of free-swimming tuna. Dorsal aortic varied from 34·5 to 91·7 mmHg, and ranged from 3·7 to 7 mmHg. Dorsal aortic blood [pHa = 7·77 ± 0·04 (8), mean ± one S.E.M. (N)] was more alkaline than ventral aortic blood [pHv = 7·65 ± 0·02 (7)]. Warming dorsal aortic blood from 25 to 35 °C in a closed system caused and to rise and pH to fall. Oxygen-combining curves for whole blood were sigmoid [mean Hill’s number = 1·72 ± 0·05 (11), range 1·57–2·0] and P50 over the pH range found in free-swimming animals was 21 ±1·75 (8) mmHg. The CO2-induced Bohr coefficient (ΔlogP50/Δ pH) was –0·59 ± 0·046 (30). Unusual features of CO2-combining curves are attributed to a significant Root effect. Although these in vitro properties of tuna whole blood are at variance with other published data on tuna they nevertheless substantiate our determinations made in vivo.
Respiratory, Circulatory And Metabolic Adjustments During Swimming In The Tufted Duck, Aythya Fuligula
Authors: Woakes A. J. , Butler P. J.
Published: April 2021

Respiratory, and some cardiovascular and metabolic, variables were measured in tufted ducks swimming at different velocities. There were no substantial changes in any of the measured variables up to a swimming speed of 0·5 m s−1. Above this speed there were progressive increases in heart rate, oxygen uptake and respiratory minute volume. At the middle of the maximum speed range (0·8ms−1) these variables were 1·7 times, 2·7 times, and 3·4 times their resting values respectively. There was, therefore, an excessive increase in ventilation (hyperventilation), compared with the extra demand for oxygen, and this was evident as a significant decrease in oxygen extraction and as a significant fall in in arterial blood.

The possible causes of the hyperventilation are not obvious as there was no hyperthermia and no change in pH of the arterial blood; a 2·3 times increase in lactic acid was balanced by the reduction in .There was some evidence of locomotor-respiratory coupling at the highest swimming speeds (leg beat frequency: respiratory frequency, 6:1), which appeared to constrain any further rise in respiratory frequency. At the highest swimming speed tidal volume, for the first time, increased above the resting value and the level of hyperventilation was increased. Hyperventilation may, therefore, serve to maintain arterial pH in the face of a metabolic acidosis.

Arterial blood pressure, and haematocrit did not change during swimming. There was a doubling in the level of plasma adrenalin with little change in noradrenalin. The possible effects of these increases are discussed.
Induction of Evisceration in the Holothurian Eupentacta Quinquesemita and Evidence for the Existence of an Endogenous Evisceration Factor
Authors: Byrne Maria
Published: April 2021

The stimuli provoking evisceration of Eupentacta quinquesemita (Selenka) and autotomy of isolated pharyngeal retractor muscle (PRM) tendons were investigated. Tendon autotomy is a two-part response involving PRM contraction and breakdown of tendon connective tissue. An evisceration factor (EF) was detected in coelomic fluid expelled during evisceration. EF was isolated in tissue extracts and the haemal system and peritoneum were sources of EF activity. Autotomy and evisceration were induced by electrical stimulation, K+ and EF, and the effect of these agents was inhibited by anaesthetics. The acetylcholine antagonist tubocurarine chloride elicited evisceration, suggesting that evisceration may involve inhibition of cholinergic transmission. Evisceration and autotomy appear to be neurally controlled and the presence of an endogenous EF suggests neurosecretory or hormonal activity. Cells involved in evisceration may be located at a distance from the autotomy tissues and effect connective tissue breakdown through the medium of the coelomic fluid. Hypothetical sequences of events and possible roles for EF are presented.
Energetics of Hermit Crabs During Locomotion: the Cost of Carrying a Shell
Authors: Herreid Clyde F. , Full Robert J.
Published: April 2021

Oxygen consumption was measured as hermit crabs (Coenobita compressus) walked at controlled velocities on a motor-driven treadmill inside a small respirometer. The crabs displayed an aerobic response to exercise with a rapid increase in reaching a steady state in about 5–6 min followed by a rapid recovery. The highest was four times the resting rate. was directly dependent on the velocity of travel (V) : . Metabolic rate was increased significantly in crabs with bilateral leg ablation.

The cost of shell carrying was evaluated by comparing of crabs with and without their protective snail shells at different velocities; the absolute difference was constant (0·7mlO2g−1 h−1), suggesting that the cost of shell support was constant per unit of time regardless of speed.

The cost of transport dropped dramatically with speed for crabs both with and without snail shells. Crabs carrying shells used twice as much O2 per gram per kilometre as did ‘nude’ crabs walking slowly at 0·02kmh−1, but the difference decreased to 1·3 times when velocity was increased 10-fold. Hermit crabs did not increase their proportionately with load: the loaded/unloaded ratio was consistently less than the mass loaded/unloaded ratio. This apparent increase in efficiency may be due to the fact that crabs carrying heavy shells alter their leg position and tend to drag their shell.

Crabs with and without shells have the same minimum cost of transport CM, so travel at the highest velocity is theoretically the most economical way to cover a given distance. Appropriately, crabs on the beach average a fast 0·23 km h−1 which produces a low cost of transport only 1·3 times higher than CM. The CM of six-legged hermit crabs is comparable to that of mammals, birds, crabs and insects of similar size and indicates that leg number does not affect fuel economy.
Human Homing: Still No Evidence Despite Geomagnetic Controls
Authors: Westby G. W. Max , Partridge Karen J.
Published: April 2021

Baker’s highly influential and widely cited studies suggest that people are capable of non-visual navigational performance comparable to that of homing pigeons. Past failures to replicate this work have been attributed by Baker to geomagnetic influences. We report a series of experiments in which both temporal and spatial geomagnetic controls were introduced. We could still find no evidence for blindfold homeward orientation in humans.
Aspects of Sensory Integration in the Crayfish Swimmeret System
Authors: Heitler W. J.
Published: April 2021

The chief sensory effects observed in response to movement and position of a single swimmeret are ipsilateral reflexes such that the amplitude of spontaneous rhythmic activity is augmented when the swimmeret is held protracted, and diminished when the swimmeret is held retracted. A major source of these reflexes appears to be the non-spiking stretch receptors (NSSRs) at the base of the swimmeret. Sinusoidally-varying current injected into a single NSSR produces a beat-frequency modulation of spontaneously-generated rhythm very similar to that produced by applying sinusoidal movement to the whole swimmeret. The spontaneous rhythm does not entrain to the applied movement. Spiking receptors responding to movement and cuticle distortion may be largely responsible for a dynamic component of the reflex, and also for inconsistently-observed arousal effects and changes in frequency of spontaneously-generated rhythms.
Fine Analysis of Predatory and Defensive Motor Events in Torpedo Marmorata (Pisces)
Authors: Belbenoit Pierre
Published: April 2021

Predation and defence of Torpedo marmorata, elicited with biological., and inanimate stimuli, were studied in experimental conditions. Patterns of responses of neonates and adults are described, and chains of separate, coordinated motor acts are defined. Jumping predation, creeping predation, defence of the disc and defence of the tail are distinguished. Each predatory behaviour consists of stimulus reaction chains, whereas defensive types of behaviour involve single stimulus reactions. During jumping behaviour, tail strokes provoked by the initial response in the chain are displayed during the whole period of predation; these ‘delayed’ tail strokes provoke displacements of the prey, thus probing the substrate and furnishing biological cues. Large behavioural variations are reported, including incomplete chains of responses, repetition of responses, oriented responses, stimulus intensity/response magnitude relationships and missing of certain motor acts. Ontogenetic maturation of the behaviour patterns is observed in embryos and in immature neonates. Sets of electric organ discharges (EODs), which accompany the defensive responses and certain predatory responses, show a stereotyped pattern, characteristic for each EOD motor act. Variations found in the EOD pattern are often related to the effects of fatigue on the EOD rate. Electric shock provokes the immobilization of the prey, or the flight of the aggressor. Effective use of the EOD by neonates as a weapon against prey is reported. The possible neuronal basis of the sensorimotor organization which may account for the results is discussed.
Morphometry Of The Gills Of The Elasmobranch Scyliorhinus Stellaris In Relation To Body Size
Authors: Hughes George M. , Perry Steven F. , Piiper Johannes
Published: April 2021

In order to study the dependence of the dimensions of the respiratory apparatus on body size and to provide a morphometric basis for the analysis of branchial gas exchange function, the gills of 12 specimens of Scyliorhinus stellaris L., weighing 0·58–2·62 kg, were examined morphometrically. The average values and the local variations of the structural parameters determining diffusive gas transfer properties of the gills were determined. Particular attention was paid to corrections for shrinkage effects in surface area measurements and to corrections for the Holmes and slant effects in measurements of paraffin sections.

The shape and size of secondary lamellae varied according to the sampling site on the filament, and filament length varied with its location on the gill arch. Also the water-blood distance varied, mainly because of frequent occurrence of thickenings at mid-height of the secondary lamellae.

The total gill surface area increased proportionally to (body mass)0·78, mainly because of an increase in surface area of individual lamellae rather than an increase in their number. Since the thickness of the secondary lamellae varied little with body mass, the observed increase in total filament length in proportion to body mass is attributed to an increase in interlamellar distance. The water-blood distance varied little with body mass.

The extent of shrinkage was found to be about 10% of filament length, but because of the compensating increase in secondary lamellar frequency this had no effect on gill area estimates, although it did affect the interlamellar dimensions. Shrinkage of individual secondary lamellae was extremely difficult to estimate, partly because of non-isometric shrinkage within the gill system. Underestimation of secondary lamellar area using paraffin sections could approach 30% mainly because of a reduction in the proportion of the pillar cell system exposed above the level of the gill filaments.
Aminergic and Peptidergic Neuromodulation in Crustacea
Authors: Beltz Barbara S. , Kravitz Edward A.
Published: April 2021

Biogenic amines and peptides can act both as circulating neurohormones and as classical central and peripheral neurotransmitters. This article reviews some of the variety of roles played by amines and peptides in crustacean nervous systems. Cardiac, stomatogastric and postural systems are used to illustrate: (1) the functional versatility of amines and peptides; (2) the molecular basis of their actions; (3) the coexistence of amines and peptides with other bioactive compounds; and (4) the developmental expression of amine and peptide phenotypes. We will deal in detail with the postural neuromuscular system of the lobster, Homarus americanus. Physiological and pharmacological experiments have shown that the biogenic amines serotonin and octopamine are capable of regulating posture by direct neurohormonal actions on the muscles and by central actions that alter motoneuronal output. We have localized serotonin to identified neurones in the lobster ventral nerve cord and have shown further that the pentapeptide proctolin coexists with the amine in these cells. Such neurones provide a convenient system in which to study the functional interactions between peptide and amine cotransmitters. In addition, the serotonin and proctolin phenotypes of these cells are first expressed at widely different times in development. This presents the possibility of studying the regulation of these two transmitter phenotypes in a system that is readily amenable to experimental manipulation.
Ionic Channels and Hormone Release From Peptidergic Nerve Terminals
Authors: Lemos José R. , Nordmann Jean J.
Published: April 2021

Although there is considerable evidence that depolarization of nerve cell terminals leads to the entry of Ca2+ and to the secretion of neurohormones and neurotransmitters, the details of how ionic currents control the release of neuroactive substances from nerve terminals are unknown. The small size of most nerve terminals has precluded direct analysis of membrane ionic currents and their influence on secretion. We now report that it is possible, using patch-clamp techniques, to study stimulus-secretion coupling in isolated peptidergic nerve terminals.

Sinus gland terminals from Cardisoma are easily isolated following collagenase treatment and appear morphologically and electrically very similar to nondissociated nerve endings. We have observed two types of single-channel currents not previously described. The first (‘f’) channel is activated by intracellular Na+ and the second (‘s’) by intracellular Ca2+. Both show little selectivity between Na+ and K+. In symmetrical K+, these cation channels have mean conductances of 69 and 213 pS, respectively. Furthermore, at least three types of Ca2+ channels can be reconstituted from nerve terminal membranes prepared from sinus glands. Nerve terminals can also be isolated from the rat neural lobe. These neuro-secretosomes release oxytocin and vasopressin, in response to membrane depolarization, only in the presence of external Ca2+. The depolarization of the nerve endings is associated with an increase in intracellular free Ca2+ concentration and this increase, measured using a fluorescent indicator, is abolished by Ca2+ channel blockers. Channels similar in their properties to the f and s channels also exist in rat neural lobe endings. Since these channels have not been found in other neurones or neuronal structures they may be unique to peptidergic nerve terminals.
The Physical Aspects of Fish Locomotion
Authors: Richardson E. G.
Published: April 2021

The resistance of an inert fish moving in water is approximately the same as that of a wooden model similar in form and moving at the same velocity. When a lamina is made to vibrate in a current of air, it exerts a thrust in the direction in which the vibrations are travelling over the lamina; as long as the velocity of movement of the vibrations exceeds that of the external current of air, the resistance of the lamina is negative. Attention is drawn to the significance of the Katzmayr effect in respect to the locomotion of fish.