bluuebunny/crossref_metadata_2025 huggingface dataset:
Glucose Transport by the in Vitro Perfused Midgut of the Blue Crab, Callinectes Sapidus
Authors: Chu Ka Hou
Published: April 2021

The midgut of Callinectes sapidus is capable of net transmural glucose absorption. The mucosal glucose influx by the midgut has a sodium-dependent, saturable component and a sodium-independent, non-saturable counterpart. The unidirectional mucosal to serosal flux and the mucosal influx of glucose are depressed by metabolic inhibitors, the presence of mucosal phlorizin or serosal ouabain. The low rate of net transmural glucose flux and the kinetic characteristics of mucosal influx suggest that the midgut does not play an important role in total nutrient absorption. Thin layer chromatographic analysis shows that most of the glucose appears as phosphorylated forms upon entering the midgut, suggesting that the efflux of free glucose across the serosal border requires an active mechanism.
Role of the Lower Intestine in the Adaptation of Gulls (Larus Glaucescens) to Sea Water
Authors: Goldstein David L. , Hughes Maryanne R. , Braun Eldon J.
Published: April 2021

We used in vivo perfusion of the lower intestine (colon plus coprodeum) to examine the osmoregulatory role of that organ in glaucous-winged gulls (Larus glaucescens Naum.) drinking sea water and fresh water. The area of the lower intestine was small, 0·59 cm2 100g-1 body mass. Its electrolyte and water transport rates were unaffected by salt water acclimation. Sodium and chloride were always reabsorbed from the intestinal lumen to the plasma. The maximum sodium transport rate we measured was 37μlequivcm-2h-1, from a sodium concentration of 200 mequiv l-1. Potassium transport from the different perfusion fluids differed, and was generally negatively correlated with sodium transport, suggesting some form of sodium-potassium exchange. Solute-linked water was reabsorbed at a rate of 3·5 μlμequiv-1 Na+, permitting the lower intestinal epithelium to maintain a luminal fluid up to 130mosmolkg-1 hyperosmotic to plasma. The serosal-to-mucosal osmotic permeability coefficient of the lower intestinal epithelium was 0·21 μlcm-2h-1 (mosmolkg-1)-1. Ureteral urine from birds in both groups was usually strongly (up to 250mosmolkg-1) hypertonic to plasma, but sodium, potassium and chloride concentrations were low and constituted less than 25 % of total osmolytes. We suggest that the lower intestine of L. glaucescens does not play a major role in reclaiming urinary water and electrolytes for recycling to the salt glands.
Influence of Oxygen on the Heartbeat Rhythm of the Leech
Authors: Davis Robin L.
Published: April 2021

Raising and lowering the oxygen content in the fluid bathing the skin of the leech modified the frequency of the heartbeat. In raised concentrations of oxygen, the period between bursts of impulses in the heart excitor motoneurones (HE cells) was reduced. Conversely, with lowered oxygen concentrations bathing the skin, the heart rate was slowed, with longer periods between bursts of firing in the HE motoneurones. Changes in oxygen concentration did not affect HE motoneurone firing patterns in preparations in which the CNS was dissected from the skin and surrounding body tissues. Various other stimuli were tried, including stroking, pinching, stretching the skin, blood vessels and gut, as well as changing the temperature. None of these stimuli mimicked the specific effects of oxygen on rhythmicity. It is concluded that peripheral receptors sensitive to changes in oxygen tension are able to influence the central neuronal circuits responsible for generating the rhythm of the heartbeat.
Octopamine Sensitivity of the Blood-Brain Barrier of an Insect
Authors: Schofield P. K. , Treherne J. E.
Published: April 2021

Octopaminergic sensitivity of the glia that form the blood-brain barrier of the cockroach was examined using microelectrode recordings of the potential developed across this barrier layer, the perineurium. Exposure to 10−4moll−1 DL-octopamine had no significant effect upon the changes in potential induced by substitution of Tris for external sodium. Treatment with concentrations ranging from 10−4moll−1 down to 5 × 10−7 mol 1”1 enhanced the resting level of the potential after 5 min, with an accompanying depression of the magnitude of potassium-induced steps. At 10−7moll−1, there was no significant effect upon the resting level, but there was a reduction in potassium sensitivity. In a study of the effect of other neurohormonal factors, it was found that DL-synephrine could depress the response to potassium but was less effective than octopamine. In contrast, carbamylcholine, histamine and some compounds related to octopamine enhanced the potassium sensitivity. The effect of octopamine was completely blocked by phentolamine, and partially blocked by propranolol. It is concluded that the perineurium possesses an octopamine receptor that could respond to octopamine circulating in the haemolymph, and which appears to mediate a reduction in the potassium sensitivity of the basolateral membrane of these glia.
A Triphasic Ventilator for Reptiles
Authors: Hasan Z.
Published: April 2021

In connection with studies of the spinal motor-control system (Hasan & Sasaki, 1986), the need arose to maintain freshwater turtles (Pseudemys scripta elegans) in a decapitated state for several days. Although a commercially available ventilator has been used in a similar situation (Rosenberg, 1972), such ventilators, apart from being expensive, are not designed to suit the reptilian respiratory pattern. In particular, they do not usually accommodate low frequencies of respiration, nor do they allow the apnoeic pauses (during which the lungs remain inflated while the glottis is constricted) that are observed in normal reptilian breathing (Wood & Lenfant, 1976; Jackson, 1979; Randall, Burggren, Farrell & Haswell, 1981). A simple, inexpensive ventilator was therefore constructed, which mimics the reptilian pattern. Its design is described here for possible use by others who may have similar requirements.
Transcellular and Paracellular Flow of Water During Secretion in the Upper Segment of the Malpighian Tubule of Rhodnius Prolixus: Solvent Drag of Molecules of Graded Size
Authors: Whittembury Guillermo , Biondi Angela C. , Paz-Aliaga Azael , Linares Henry , Parthe Valentín , Linares Nancy
Published: April 2021

The following molecules graded in size were added to the fluid bathing the blind end of the upper segment of the Malpighian tubules of Rhodnius: urea (U), erythritol (E), mannitol (M), L-glucose (G), sucrose (S), polyethyleneglycol 800 (PEG), raffinose (R), inulin (I) and dextran 15 000–18 000 (D). U, E, M and G distribute themselves within the cell and the extracellular space, while S, PEG, R, I and D are exclusively extracellular. In addition, the net secretory flow of these probes was studied as a function of the net secretory volume flow (Jv). , is made up of a diffusive component , mainly due to unstirred layer effects, and of a convective component , due to the drag (entrainment) of the probes by the water flow. The relative contribution of and of for each probe was studied as a function of Jv. It was found that for U, E, M, G, S and PEG. Therefore these probes are dragged by water. On the other hand for R, I and D, which are not entrained. It is concluded that water flows via extracellular pathways since S and PEG, which are true extracellular probes, are entrained by solvent. In addition to extracellular pathways, it is suggested that the transcellular structures described by Wessing (1965) and Bergeron et al. (1985) could also be the sites of solute-solvent coupling.
Osmotic Effects on Amino Acid Oxidation in Skate Liver Mitochondria
Authors: Moyes Christopher D. , Moon Thomas W. , Ballantyne James S.
Published: April 2021

The mechanism responsible for the osmotic sensitivity of sarcosine oxidation by liver mitochondria from the little skate, Raja erinacea Mitchill, is examined. Assay medium tonicity, rather than a solute effect (urea or trimethylamine oxide), is probably responsible for the inverse relationship between osmolarity and the rate of oxidation of sarcosine by these mitochondria. Sarcosine oxidation proceeds through the flavin-linked sarcosine oxidase with the resultant glycine catabolized in the NAD-linked glycine cleavage system. The tonicity-sensitive component of the sarcosine oxidative pathway is not the glycine cleavage system. Sarcosine oxidation in the presence of rotenone is sensitive to medium tonicity. Oxidation of serine, which is also catabolized through the glycine cleavage system, is not as sensitive to tonicity as is sarcosine oxidation. Mitochondrial volume changes also appear to affect the transport of glycine. Although sarcosine does not appear to share the glycine transporter, it is possible that sarcosine transport is similarly sensitive to medium tonicity. The effects of osmolarity on the oxidation of dimethylglycine appear to support this hypothesis. Tonicity effects on sarcosine oxidase cannot yet be eliminated.
Cholinergic Action on the Heart of the Leech, Hirudo Medicinalis
Authors: Calabrese Ronald L. , Maranto Anthony R.
Published: April 2021

Experiments were performed to determine the role of acetylcholine (ACh) in neuromuscular transmission in the heart of the leech Hirudo medicinalis.

Superfused or iontophoretically applied ACh rapidly depolarized both isolated heart muscle cells and muscle cells in isolated hearts in a dose-dependent manner. The depolarization was associated with a conductance increase of the muscle membrane that had a reversal potential of −9 mV. Eserine potentiated the response to superfused ACh, reducing the threshold from 10−6 to 10−8moll−1. Acetylcholinesterase was localized histochemically to be in the immediate area of neuromuscular terminals. Superfused nicotinic agonists mimicked the effects of ACh, while superfused nicotinic antagonists reversibly blocked the iontophoretic response of heart muscle fibres to ACh. 5×10−7moll−1 curare, 5x10−5moll−1 nicotine and l×10−4moll−1 atropine reduced the iontophoretic response to half its original amplitude. Alpha-bungarotoxin did not block the response of heart muscle cells to iontophoretically applied ACh. Curare was used to determine whether the neurones that innervate the heart - HE motor neurones and HA modulatory neurones - use ACh as a neuromuscular transmitter. The fast depolarizing component of the HE cell’s neuromuscular transmission was reversibly blocked by 10−4moll−1 curare, while the HA cell’s modulatory effects on the heart were apparently unaffected by 10−4moll−1 curare.

Our results indicate that heart muscle cells have nicotinic acetylcholine receptors that open in the presence of ACh, thereby increasing membrane conductance. The HE motor neurone is probably cholinergic and engages these receptors in its neuromuscular transmission, while the HA modulatory neurone is probably not cholinergic.
The Segmental Giant Neurone of the Hermit Crab Eupagurus Bernhardus
Authors: Heitler W. J. , Fraser K.
Published: April 2021

The anatomy and physiology of the segmental giant (SG) neurone of the fourth abdominal ganglion of the hermit crab is described. The SG has an apparently blindending axon in the first root and a small cell body in the anterior ipsilateral ventral quadrant of the ganglion. There is a large ipsilateral neuropile arborization with prominent dendrites lined up along the course of the ipsilateral giant fibre (GF). The SG receives 1:1 input from the ipsilateral GF via an electrical synapse which is usually rectifying. SG activation produces a large EPSP in all ipsilateral and some contralateral fast flexor excitor (FF) motor neurones. The major input to FFs resulting from GF activation appears to be mediated via the SG. It also produces a small EPSP in ipsilateral and contralateral motor giant neurones. The properties of the hermit crab SG are compared to those of the crayfish SG, and the implications of the SG for the possible evolutionary paths of the giant fibre system are discussed.
The Wake of A Jackdaw (Corvus Monedula) in Slow Flight
Authors: Spedding G. R.
Published: April 2021

The wake of a jackdaw in slow forward flight is described. The three-dimensional velocity field was investigated qualitatively and quantitatively by analysis of multiple-flash stereophotographs of the motion of neutrally buoyant helium bubbles. The best description of the wake structure appears to be a chain of planar, nearcircular, discrete, small-cored, vortex loops, each produced by vorticity shed during a single downstroke.

However, the momentum measured in such a wake is approximately 35 % of that required for weight support under these flight conditions. Some evidence is presented that this apparent wake momentum deficit may arise because the description of the real wake vorticity distribution is too simplistic.

The implications of these results for theoretical models of bird flight are briefly discussed.
Adduction Levers And Adductor Muscle Function in the Mandibular System of the Shore Crab Carcinus Maenas
Authors: Abby-Kalio N. J. , Warner G. F.
Published: April 2021

The lever systems, and structure and function of the adductor muscles, of the mandibles of large male Carcinus maenas (L.) were investigated. The functional mechanical advantage (FMA) of the external adductor muscles, measured at the middle of the biting edge of the mandible, was 1·53 ± 0·01; the ideal mechanical advantage (IMA), calculated from measured lever lengths, was 1·78 ± 0·03 (mean ± S.E.). The FMA of the internal adductor muscles was 0·53 ± 0·01 and the IMA was 0·62 ±0·02

When slowly loaded, the external adductor system broke at 3·09 ± 0·16 N; when rapidly loaded, the system broke at 7·16 ± 0·79 N. Short duration loading at 2·0 N or more was found to result in histologically detectable damage at the pivot. When slowly loaded, the internal adductor system broke at 0·68 ± 0·05 N. When a load of 0·39 N was applied to the internal adductor system, the failure point on slow loading of the external adductor system was not significantly increased.

The mean maximum force of contraction of the external adductor muscles on electrical stimulation was 0·98 ± 0·03 N, with a stress of 627 kN m-2 in the fibres. The internal adductors contracted with a mean maximum force of 0·33 ± 0·01 N. The total maximum bite force is therefore about 3·3 N, only 10% being contributed by the internal adductors. The safety factor of both internal and external systems is about 2.

The mean sarcomere length of half-contracted fibres of the external adductor muscles was 11· 62 ± 0·11 μm.
Perfusion-Secretion Relationships in the Isolated Elasmobranch Rectal Gland
Authors: Shuttleworth T. J. , Thompson J. L.
Published: April 2021

Perfusion and sodium secretion parameters were measured in the isolated rectal gland of Scyliorhinus canicula L. perfused at in vivo pressures, and the effect of stimulation of secretory activity by cyclic AMP and theophylline on these parameters was determined. Stimulation resulted in large increases in secretion flow rate, percentage extraction of sodium from the perfusing fluid, and arteriovenous sodium concentration difference, but did not affect perfusion flow rate or the sodium concentration of the secreted fluid. Reduction of perfusion flow rate to values below 65% of the control level, achieved by reducing perfusion pressure, produced a marked decline in sodium secretion -a process accompanied by increases in the percentage extraction of sodium and arteriovenous concentration difference of sodium, but again without any change in the sodium concentration of the secreted fluid. The in vivo consequences of these findings are discussed with reference to related findings for the avian nasal salt gland.

The normal rate of secretion, its sodium concentration, and the nature of the dependence of secretion rate on perfusion flow below certain levels, were essentially unaffected by a reduction in the availability of oxygen to the gland by approximately 80%. It is concluded that the observed relationship between perfusion flow and sodium secretion rate in the stimulated gland is not related to oxygen availability, and hence that the primary underlying function of the synchronized secretion-related vasodilation seen in the gland is not to increase the supply of oxygen to the stimulated secretory tissue. We discuss possible reasons why this erroneous conclusion has been reached by other workers.
Multimodality of Ocellar Interneurones of the American Cockroach
Authors: Ohyama Takahiro , Toh Yoshihiro
Published: April 2021

Many insects possess two or three dorsal ocelli in addition to the paired compound eyes. The dorsal ocellus is characterized by a high convergent ratio of many retinular axons upon several thick second-order neurones in the posterior region of the ocellus. The thick second-order neurones extend towards the brain as an ocellar nerve together with other thin processes, and their central projections have been well demonstrated by cobalt backfills in many insects (reviewed by Goodman, 1981). However, our knowledge about how information is processed in the ocellar system is limited (but see Chappell & Dowling, 1972; Wilson, 1978a,b; Goodman, 1981; Simmons, 1981). In the present study we present some evidence that in the cockroach, Periplaneta americana, the ocellar second-order neurones function as CNS integrative multimodal neurones.
Natural and Induced Magnetization in the Bobolink, Dolichonyx Oryzivorus (Aves: Icteridae)
Authors: Beason Robert C. , Brennan William J.
Published: April 2021

The magnetic characteristics of the heads from 28 bobolinks [Icteridae: Dolichonyx oryzivorus (L.)] were analysed using remanence magnetometers. The natural remanent magnetization of 12 freshly preserved heads averaged 3·20×10−7 electromagnetic units (e.m.u.) (le.m.u. = 103Am−1) and was oriented horizontally from side to side. An electromagnet was used to induce magnetization with external field strengths of up to 0·7 Tesla (T). The average saturation isothermal remanent magnetization (sIRM) for 23 bobolink heads was 2·49X10−5 e.m.u. Because the IRM was attained partially below 0·1 T and totally below 0·3 T, we believe that the magnetic material in the bobolink is at least partially single domain magnetite. The relationship between the IRM acquisition and alternating field (a.f.) demagnetization curves indicates that the single or pseudo-single domain grains of magnetite interact. Similar results were obtained on one savannah sparrow (Emberizidae: Passerculus sandwichensis) head and one indigo bunting (Emberizidae: Passerine cyanea) head.

When some bobolink heads were subdivided, most or all of the magnetization was concentrated in the area from the nasal cavity to the orbit. Light microscopy and histochemical tests confirm the localization of inorganic iron in this region.
Action Potentials in Rhodnius Oocytes: Repolarization is Sensitive to Potassium Channel Blockers
Authors: O’Donnell M. J.
Published: April 2021

Depolarization of Rhodnius oocytes evokes action potentials (APs) whose rising phase is calcium-dependent. The ionic basis for the repolarizing (i.e. falling) phase of the AP was examined.

Addition of potassium channel blockers (tetraethylammonium, tetrabutylammonium, 4-aminopyridine, atropine) to the bathing saline increased the duration and overshoot of APs. Intracellular injection of tetraethylammonium had similar effects. These results suggest that a voltage-dependent potassium conductance normally contributes to repolarization. Repolarization does not require a chloride influx, because substitution of impermeant anions for chloride did not increase AP duration. AP duration and overshoot actually decreased progressively when chloride levels were reduced.

Current/voltage curves show inward and outward rectification, properties often associated with potassium conductances. Outward rectification was largely blocked by external tetraethylammonium. Possible functions of the rectifying properties of the oocyte membrane are discussed.
Gas exchange, storage and transport in voluntarily diving Xenopus laevis
Authors: Boutilier R. G. , Shelton G.
Published: April 2021

A closed, extracorporeal loop, containing oxygen and carbon dioxide electrodes, was developed in order to make continuous measurements of lung gas and in undisturbed Xenopus laevis. Pulmonary R values are about 0 ·8 during periods of lung ventilation in resting animals, but they fall very rapidly as a voluntary dive proceeds. In fact, the instantaneous R values for lung eventually fall to zero during a voluntary dive, since continues to decline whilst (after an initial increase) comes into a steady state as transcutaneous CO2 losses balance metabolic production. These relationships change during spontaneous underwater activity, aquatic hypercapnia or enforced diving, with significantly higher levels being found at any value than in resting animals. Emergence from such dives is marked by a considerable hyperventilation, leading to lung R values which are 2–3 times higher than those seen during lung ventilation of animals at rest. The lungs of Xenopus are therefore important in eliminating the CO2 stored during a period of breath-holding but not of major importance in forming part of that store themselves.

The lungs of Xenopus are, however, important sources of stored oxygen during voluntary dives, the rate of use being clearly related to activity levels and dive durations. There could be sudden changes in the rate of depletion during a dive, suggesting that factors additional to the metabolic rate of the cells may be important in determining the way in which the lung store is used.

In a parallel series of experiments, O2 and CO2 partial pressures were determined in lung gas samples and in simultaneously drawn samples of blood from the femoral artery (systemic arterial) and left auricle (pulmonary venous) of animals making voluntary dives. These blood/gas data, together with results of previous experiments on Xenopus, have been used to develop an idealized model of O2 exchange, storage and transport during a 30-min voluntary dive. The volume of the O2 stores held in the lungs and various subdivisions of the circulation are shown in the model by plotting the of the store against its respective O2 capacitance. The model illustrates the overall importance of the lung as a source of oxygen during breathholding and that early use of a large systemic venous O2 store may be an important basic function for cardiovascular adjustments seen in a dive.
Electrophysiological Studies on the Temporal Organ of the Japanese House Centipede, Thereuonema Hilgendorfi
Authors: Yamana Kenjiro , Toh Yoshihiro , Tateda Hideki
Published: April 2021

The response of the temporal organ (organ of Tömösváry) has been studied electrophysiologically in the Japanese house centipede (Thereuonema hilgendorfi : Chilopoda).

Receptor cells of the temporal organ show spontaneous discharges (15–40 impulses s-1) which are depressed in a phasic-tonic manner by carbon dioxide stimuli. Perfusion of the presumed receptor site with a carbon dioxide-containing solution also changes the impulse frequency. The impulse frequency of a receptor cell decreases linearly with a logarithmic increase in carbon dioxide concentration ranging from 0·001 % to 0·1 % in the phasic state and from 0·05% to 5·0% in the tonic state. These results suggest that the temporal organ of the house centipede functions as a carbon dioxide receptor, though it responds to other stimuli as described below. Changing the pH of a carbon dioxide-containing solution changes the impulse frequency, probably by changing the molar fraction of CO2 molecules in the lymph surrounding the receptor site. pH also directly influences the impulse frequency of the receptor cell, but the effect is smaller than that of CO2 molecules. Receptor cells respond to humidity changes, but the response is smaller than that to carbon dioxide. When receptor cells are stimulated by moist air (100% relative humidity, RH) after adaptation to dry air (0% RH), the impulse frequency increases by a factor of 1·29 ±0·37 (mean ± S.D. measured for the first second, N = 29), and 1·16 ± 0·28 (measured after adaptation to moist air, N = 29). Air-borne chemicals also affect the impulse frequency of a receptor cell; it is increased by amines and decreased by fatty acids and aldehydes. Effects of these chemicals are discussed in relation to changing the pH of lymph bathing the receptor site.
The relative distribution of pulmocutaneous blood flow in Rana catesbeiana: effects of pulmonary or cutaneous hypoxia
Authors: Boutilier R. G. , Glass M. L. , Heisler N.
Published: April 2021

The distribution of pulmocutaneous heart output to lungs and skin was determined in non-anaesthetized, fully recovered bullfrogs (Rana catesbeiana) by application of the microsphere method in order to study the modulation of blood flow to different gas exchange sites in amphibians during environmental air and water hypoxia. The relative perfusion of various skin areas was found to be rather heterogeneously distributed with an over-proportionately high blood flow to the ventral body surface. This distribution of flow among different skin areas remained unaffected by any type of environmental hypoxia. The relative perfusion of lungs and skin, however, was significantly affected by the pattern of environmental oxygen partial pressure. The relative lung perfusion (≈80 % of pulmocutaneous flow in normoxic control conditions) was increased during water hypoxia, and reduced with lowered inspired . This mechanism could be interpreted as a readjustment of blood flow towards the gas exchange site with higher oxygen partial pressure, but may also represent a mechanism to prevent oxygen loss from the body stores at gas exchange sites of low oxygen tension.
The absence of an arterial pressure effect on filtration by perfused glomeruli of the hagfish, Eptatretus stouti (Lockington)
Authors: Riegel J. A.
Published: April 2021

Single renal corpuscles of hagfish were perfused with a Ringer solution containing Ficoll 70 to simulate the colloid osmotic pressure of hagfish plasma. Simultaneous measurements were made of single glomerulus filtration rate (SGFR), perfusion pressure and the pressure in a vessel of the renal vasculature. The results confirm that SGFR is independent of pressure in the glomerular capillaries (PGC). The results also suggest that flow through glomeruli and SGFR are closely linked. Studies of the pressures in glomerular capillaries during periods when the perfusion rate was varied indicate that PGC reflects the area of the active capillaries and the rate of perfusion. Therefore, in the hagfish, PGC appears to be an effect of factors that cause glomerular filtration, not the main cause of that process.
Iron-containing cells in the honey-bee (Apis mellifera): I. Adult morphology and physiology
Authors: Kuterbach D. A. , Walcott B.
Published: April 2021

Particulate iron was found within the trophocytes of the fat body of the adult honey-bee. These iron granules differed in their structure and composition from iron granules found in other biological systems. The granules had an average diameter of 0·32 ± 0·07 μm and were composed of iron, calcium and phosphorus in a noncrystalline arrangement. The granules were apparently randomly distributed within the cytoplasm of the cells, and were not associated with any particular cellular organelle.

Electron microscopy revealed the presence of cell junctions between the trophocytes. In tissues treated with colloidal lanthanum, 20-nm gaps were seen between the outer leaflets of the cells forming the cell junction. Physiological studies showed that these cells are electrically coupled, but the coupling ratio is low, as a result of extensive coupling to many cells.
Iron-containing cells in the honey-bee (Apis mellifera): II. accumulation during development
Authors: Kuterbach D. A. , Walcott B.
Published: April 2021

The development of iron granules in honey-bee tissues was investigated using both anatomical and analytical methods. Iron granules are present only in the trophocytes of post-eclosion adults and have the same elemental composition as those in foraging adults. The granules increase in both size and number during ageing. Iron levels in developing worker honey-bees were measured by proton-induced X-ray emission spectroscopy. The rate of iron accumulation was directly related to iron levels in the diet, and the iron can be obtained from pollen and honey, both major food sources of the bee. In adults, the iron content of the fat body reached a maximum level (2·4 ± 0·15 μgmg−1 tissue), regardless of the amount of iron available for ingestion. Maximal iron levels are reached at the time when honey-bee workers commence foraging behaviour, suggesting that iron granules may play a role in orientation. Alternatively, accumulation of iron in granules may be a method of maintaining iron homeostasis.
The Modulatory Actions of FMRFamide and Related Peptides on Locust Skeletal Muscle
Authors: Evans Peter D. , Myers Camilla M.
Published: April 2021

The modulatory actions of FMRFamide and related peptides on tension generated in the extensor-tibiae muscle of the locust hindleg by stimulation of the slow excitatory motor neurone (SETi) depend upon the frequency of stimulation of SETi. They have no effect on the tension induced by the fast motor neurone (FETi) or upon the myogenic rhythm present in this muscle. At low frequencies of SETi stimulation (1Hz and below) the predominant modulatory effects are increases in the amplitude, contraction rates and relaxation rates of twitch tension. At higher frequencies, where twitches summate but tetanus is incomplete (up to 20 Hz) these effects are superimposed upon an increase of maintained tension. FMRF amide increases the amplitude and relaxation rate of slow twitch tension by different amounts in different regions of the extensor muscle. It is likely that the effects of FMRF amide are restricted to slow muscle fibres that are innervated by SETi but not FETi. The modulatory actions of FMRFamide on SETi-induced tension are additive to, but do not potentiate, the modulatory actions of octopamine and proctolin in this muscle. The actions of FMRFamide show some similarities with the modulatory actions of octopamine in this preparation but they are mediated by an independent receptor system that does not change cyclic nucleotide levels. Other actions of FMRFamide are similar to the actions of proctolin.
Slow Active Potentials in Walking-Leg Motor Neurones Triggered by Non-Spiking Proprioceptive Afferents in the Crayfish
Authors: Sillar Keith T. , Elson Robert C.
Published: April 2021

Intracellular recordings have been made from walking-leg motor neurones of the crayfish, Pacifastacus leniusculus, in isolated preparations of the thoracic ganglia. Some motor neurones display slow depolarizations that can drive bursts of spikes and resemble ‘plateau’ potentials described in other invertebrate and vertebrate neurones. Evidence is presented which suggests that the potentials are regenerative and endogenous to the motor neurones, and are not the result of feedback from a neural network.

These potentials can be induced by synaptic inputs from the non-spiking afferent neurones of the thoracic-coxal muscle receptor organ, a basal limb proprioceptor. Reflex input from this receptor is augmented during the active depolarization of the motor neurone. The results are discussed in terms of the control of rhythmic motor output and the central modulation of reflexes in the crayfish’s thoracic nervous system.
Ventilation and partitioning of oxygen uptake in the frog Rana pipiens: effects of hypoxia and activity
Authors: Pinder A. W. , Burggren W. W.
Published: April 2021

Pulmonary and cutaneous oxygen uptake and lung ventilation were measured in frogs floating in water with access to air in respirometers, with and without ventilation of the skin provided by stirring. The frogs were exposed to hypoxia in both water and air, and were variably active.

In inactive frogs floating in unstirred respirometers at 25°C, 23% of total is through the skin. Activity of the animal increases total and also ventilates the skin, so that cutaneous increases with increasing total . When the respirometer is stirred, cutaneous increases to 35 % of total in resting animals. Activity no longer affects cutaneous .

Lung ventilation volume is directly proportional to lung ventilation rate in normoxia. Ventilation rate, and therefore ventilation volume, is proportional to pulmonary . Ventilation rate approximately doubles in hypoxia . The pattern of ventilation also changes in hypoxia, from a very irregular pattern in normoxia to one showing regular, large oscillations of lung volume over several ventilation movements.

Increased lung ventilation, enhancing pulmonary , is the primary adjustment to increased O2 demand. Partitioning of shifts towards the lung during both activity and hypoxia. In both cases, however, ventilation of the skin can supplement total by increasing absolute levels of cutaneous .
Thermal dependence of contractile properties of skeletal muscle from the lizard Sceloporus occidentalis with comments on methods for fitting and comparing force-velocity curves
Authors: Marsh R. L. , Bennett A. F.
Published: April 2021

The isometric and isotonic contractile properties of fast-twitch glycolytic fibres of the iliofibularis muscle (FG-IF) in the lizard Sceloporus occidentalis were measured in vitro at 5°C intervals from 10 to 40°C. The mean isometric parameters at 35°C, the preferred body temperature of this species, were as follows: maximum isometric force (Po), 187 ± 8 (S.E.M.) kN m-2; ratio of twitch force to tetanic force (PTW/P0)> 0·46 ± 0·02; time to peak twitch tension (tPTw), 7·0 ± 0·3 ms; and time from peak twitch force to 50% relaxation (t50%R), 8·2 ±0·3 ms. From 20 to 35°C P0 was almost constant (within 8% of the value at 35°C). At 10 and 15°C Po dropped to approximately 80 % of the value at 35°C. P0 was very unstable at 40°C. PTW/P0 was almost constant at all temperatures. The time-related isometric parameters were positively modified by temperature at all temperatures measured (Q10> 1·9).

The force-velocity curves of the FG-IF deviated from the simple hyperbolic relation of A. V. Hill’ s characteristic equation. We present two alternative equations for fitting these data. These equations resulted in residual sums of squares from nonlinear least-squares analysis that were at least seven-fold lower than those from Hill’ s equation. The equation that best describes our data is a hyperbola modified by the addition of a linear component: To describe the curvature of this or any other force-velocity relationship, we propose the power ratio, Ẇmax/VmaxP0 (where Ẇmax is the maximum power calculated from the force-velocity relationship and Vmax is the predicted maximum velocity of shortening at zero force).

Vmax of the FG-IF was 21·9L0s-1 at 35°C (where L0 is muscle length). This parameter was directly related to temperature between 10 and 35 °C with Q10> 1·8. The shape of the force-velocity curve is not influenced by temperature (Ẇ max/ Vmax P0 = 0·11).
Single-Channel Studies of the Action of ( + )-Tubocurarine on Locust Muscle Glutamate Receptors
Authors: Kerry C. J. , Ramsey R. L. , Sansom M. S. P. , Usherwood P. N. R. , Washio H.
Published: April 2021

The effects of ( + )-tubocurarine (TC) on single glutamate-activated channels in voltage-clamped locust muscle fibres have been examined using the patch-clamp technique. Glutamate alone produced a concentration-dependent increase in the probability of the channel being in the open state (po), but an increase in the concentration of glutamate (5× 10−5–5× 10−3 moll−1) in the presence of 5× 10−4 moll−1 TC left po essentially unchanged. TC (5× 10−6–5× 10−4moll−1) caused a concentration-dependent decrease in the mean open time and in po for channels opened by 10−4moll−1 glutamate. Correlations between successive openings and successive closings, which are characteristic of the kinetics of the muscle glutamate-receptorgated channel of locust muscle, were weakened in the presence of TC. There was little evidence of voltage sensitivity of TC action over the limited membrane potential (Vm) range —70 to —120 mV. The results are consistent with the idea that TC blocks the cation-selective channel gated by glutamate receptors in insect muscle and that the unblocking rate is low. They suggest also that block is at the level of the open channel, a conclusion supported by the wholly activation-induced depression of the neurally evoked twitch contraction of locust muscle by TC. Based upon a simple model for open channel block, TC is estimated to have a dissociation constant of 1·57μmoll−1 (Vm = — 100mV). The rate of association of blocker with channel is estimated to be 8·74×103ms−1 (moll−1)−1 (Vm= –100mV). The rate of dissociation, estimated indirectly from the single-channel data, is 1·53× 10−2ms−1, which gives a mean channel block time of 65·4 ms.
Internal Hypoxia-Hypercapnia in Tench Exposed to Aluminium in Acid Water: Effects on Blood Gas Transport, Acid-Base Status and Electrolyte Composition in Arterial Blood
Authors: Jensen Frank B. , Weber Roy E.
Published: April 2021

Tench exposed for 6 days to acid (pH 5) hard water ([Caz+] = 3·5 mmol I−1) in the presence of aluminium (2 mg I−1) showed a rapid decrease (within 3 h) in dorsal aortic and a simultaneous rise in -Arterial oxygen content and haemoglobin oxygen (Hb-O2) saturation decreased sharply, as did red cell [Hb], whereas blood haematocrit (Het) and [Hb] increased. Red cell nucleoside triphosphate (NTP) content was reduced within 1 day through a selective reduction in guanosine triphosphate (GTP).

Although the rising caused an extracellular acidosis (to which lactic acid production and perhaps H+ influx at the gills contributed), red cell pH increased compared to control values, mainly as a result of the decrease in Hb-O2 saturation. Plasma [Cl−] declined, whereas [HCO3−], [K+] and [Ca2+] increased. Ionic disturbances, however, were small compared to the changes in blood O2 transport, which appeared to correlate with high ambient [Ca2+],

Tench exhibited a high tolerance to the acid-Al exposure and most of the above parameters showed partial recovery within 1–2 days. In some specimens, however, the exposure was lethal because of an obstruction of gill function, and arterial blood became almost completely deoxygenated and showed very low pH values and high lactate concentrations, attesting to deep internal hypoxia.
A possible role for protein dissociation in the functioning of embryonic haemoglobins
Authors: Brittain T.
Published: April 2021

During early mammalian development the changing demands for oxygen in embryonic tissues are met, in part, by the synthesis of a series of embryonic haemoglobins. At the earliest stages of development three embryonic haemoglobins are synthesized in both humans and mice (Melderis, Steinheider & Ostertag, 1974; Shimizu & Watanabe, 1978; Brotherton, Chui, Gauldie & Patterson, 1979; Purdie, Wells & Brittain, 1983; Brittain & Wells, 1983). The proportions of each haemoglobin present in the mouse red blood cells vary significantly from the ninth day of gestation until parturition (Purdie et al. 1983). Although studies have been made on this developmental system of gene switching and haemoglobin composition (Brotherton et al. 1979) very few studies have been made on the functional characteristics of these embryonic haemoglobins, mainly because of the limited amount of material available (Bauer et al. 1975 ; Brittain & Wells, 1983 ; Purdie et al. 1983). The oxygen binding curves for whole blood from the earliest embryos show anomalous binding patterns (Wells & Brittain, 1981; Purdie et al. 1983; Brittain & Wells, 1983). The high oxygen affinity component present in the red blood cells of early embryonic mice has been correlated with the presence of embryonic haemoglobin El, which has a subunit structure χ2ϵ2 (Melderis et al. 1974). This haemoglobin species El shows very low cooperativity in both its equilibrium and kinetic functions (Purdie et al. 1983; Brittain, Sutherland & Greenwood, 1986). Recent investigations have indicated that the functioning of this haemoglobin is not related to any unusual redox balance within the embryonic red blood cell (Brittain & Tottle, 1986) and thus the occurrence of an essentially non-cooperative haemoglobin with a tetrameric subunit structure has posed something of a paradox. This study presents data on the dimerization of mouse embryonic haemoglobin El over a range of conditions and, together with numerical simulations of oxygen binding curves, illustrates how, within the early embryonic red blood cell, high oxygen affinity and sensitivity to pH may be obtained by protein dimerization.
Regulation of Tarsal Taste Threshold in the Blowfly, Phormia Regina
Authors: Edgecomb Robert S. , Murdock Larry L. , Smith André B. , Stephen Margaret D.
Published: April 2021

The nutritional condition of adult blowflies (Phormia regina Meigen) affects their readiness to respond with proboscis extension when their tarsi contact food stimuli. Thresholds are high in sated flies (100–1000 mmol I−1 sucrose) and low in starved flies (1–10 mmol I−1 sucrose). Two feeding regimes employing aqueous sucrose were used to reveal factors regulating tarsal taste threshold in this insect: long-term feeding (ad libitum) and single meals administered to starved flies.

A positive logarithmic relationship was found between crop weight and tarsal taste threshold, expressed as mean acceptance threshold, in flies fed aqueous sucrose ad libitum for 4 days. Threshold changes after a single meal were positively correlated to both concentration and volume of the sugar solution fed. Thresholds observed in flies fed a single meal were not as high as those in ad libitum-fed flies having the same crop volume.

Nerve-transection experiments demonstrated that the median abdominal nerve plays no direct role in threshold regulation in either single-meal-fed or ad libitum-ied flies. Transection of the recurrent nerve (RN), however, significantly attenuated the post-feeding rise in tarsal threshold in starved flies fed a single meal and markedly reduced threshold in sated flies fed ad libitum. Thresholds for RN-transected flies subjected to either feeding regime were still significantly higher than thresholds for starved flies. Haemocoel-injected D-glucose did not significantly elevate threshold in starved flies.

These observations establish that the RN plays an important role in the regulation of tarsal taste threshold in blowflies. The effect of the RN on threshold depends largely on the prior feeding activity of the flies. It appears, however, that other factors, in addition to the recurrent nerve, affect taste threshold after feeding.
Studies of the cardiac-like action potential in crayfish giant axons induced by platinized tungsten metal electrodes
Authors: Orr L. A. , Lieberman E. M.
Published: April 2021

A lightly platinized tungsten (Pt-W) wire electrode, axially inserted into a crayfish giant axon, causes the development of cardiac-like action potentials with durations of up to 4 s. The plateau in membrane potential typically occurs within 10 min of the start of action potential elongation. The effect occurs without passing current through the Pt-W electrode and is temporally related to a dramatic decrease in intracellular pH (pH,). Such an effect cannot be induced by a decrease in pH, produced by equilibrating the axon with HCO3−-CO2 solution (pH 6), an NH4C1 rebound or direct intracellular injection of PO43− buffer (pH 4 5). Action potential elongation is accompanied by a block of delayed rectification and the possibility that inward rectification also develops cannot be ruled out. Plateau generation requires Na+ and Caz+ inward currents as demonstrated by abolition of the plateau by [Na+]o or [Ca2+]o depletion or treatment with tetrodotoxin (TTX) or verapamil. The block of outward rectification by Pt-W requires external Na+ or Ca2+. Action potential elongation produced by 3,4-diaminopyridine is not sensitive to verapamil and the waveform is different from that produced by Pt-W. The data support the possibility that different classes of excitable membranes have similar channel populations and that the functional differences between them reside in the inhibitory or masking influences that are present in the microenvironments of the various membrane channels.
The Sulphide-Binding Protein in the Blood of the Vestimentiferan Tube-Worm, Riftia Pachyptila, is the Extracellular Haemoglobin
Authors: Arp Alissa J. , Childress James J. , Vetter Russell D.
Published: April 2021

The sulphide-binding protein that occurs in high concentrations in the vascular blood and coelomic fluid of the hydrothermal vent tube-worm Riftia pachyptila Jones is the haemoglobin. Sulphide binding does not occur at the oxygen-binding sites of the haem, but may occur via thiol-disulphide exchange at the interchain disulphide bridges on the macromolecule. We have confirmed the report that vascular blood is heterogeneous for two haemoglobins (FI and FII) that are different in MT, but we conclude that the coelomic fluid is homogeneous for the lower Mr haemoglobin FII, in the intact, living animal. These two haemoglobins occur naturally in the living animals, and FII is not a dissociation product of the higher Mr FI. The sulphide-binding capacities of the two haemoglobin species differ by about a factor of two. Consequently, the vascular blood and the coelomic fluid also have different sulphide-binding capacities. These differences in sulphide-binding capacity may have important ramifications for the physiology of this unusual animal.
The effects of prolonged epinephrine infusion on the physiology of the rainbow trout, Salmo gairdneri: I. Blood respiratory, acid-base and ionic states
Authors: Perry S. F. , Vermette M. G.
Published: April 2021

Rainbow trout were infused continuously for 24 h with epinephrine in order to elevate circulating levels of this hormone to those measured during periods of acute extracellular acidosis (approximately 5×l0−8moll−1). Concomitant effects on selected blood respiratory, acid–base and ionic variables were evaluated. Infusion of epinephrine caused a transient respiratory acidosis as a result of hypoventilation and/or inhibition of red blood cell (RBC) bicarbonate dehydration. The acidosis was regulated by gradual accumulation of plasma bicarbonate. Even though whole blood pH (pHe) was depressed by 0·16 units, RBC pH (pHi) remained constant, thereby causing the transmembrane pH gradient (pHe–pHi) to decrease. A similar effect of epinephrine on RBC pH was observed in vitro, although the response required a higher concentration of epinephrine (2·0× 10−7 mol I−1). We speculate that the release of epinephrine during periods of depressed blood pH is important for preventing excessive shifts in RBC pH and for initiating a series of responses leading to plasma HCO3− accumulation and eventual restoration of blood acid-base status.