bluuebunny/crossref_metadata_2025 huggingface dataset:
A stimulus paradigm for analysis of near-field hydrodynamic sensitivity in crustaceans
Authors: Wilkens Lon A. , Douglass John K.
Published: April 2021

We present several relatively simple procedures for studying the physiology of near-field mechanoreceptors in crustaceans which extend previous measures of sensitivity. The advantages include the quantitative analysis of range fractionation and directionality of receptors and interneurons in the sensory hierarchy of the central nervous system (CNS), based on a stimulus paradigm that is reproducible and easy to use. The technical considerations for quantitative fluid-coupled stimulation addressed by this paper are the complexity of dipole flow fields, reflected interference from traveling waves, and the underlying stimulus wave form. The techniques described here offer corresponding advantages for physiological experiments using other aquatic organisms.
The physiology of sensory cells in the ventral scoloparium of the stick insect femoral chordotonal organ
Authors: Büschges Ansgar
Published: April 2021

The leg joints of invertebrates are governed by neural control loops that control their position and velocity during movements (for reviews, see Bässler, 1983, 1993). These neural control loops rely on sensory feedback about the position and velocity of the controlled leg joint. In invertebrates, this sensory feedback is provided by external (e.g. hair fields, hair rows) and/or internal sense organs (e.g. chordotonal organs). The femoral chordotonal organ (fCO) serves as the main proprioceptor in the control loop governing the femur–tibia (FT) joint of the insect leg. The fCO measures the position and movement of this joint (e.g. Bässler, 1965, 1993; Burns, 1974; Usherwood et al. 1968; Zill, 1985).
Modulation of ionic currents by dopamine in an interneurone of the respiratory central pattern generator of Lymnaea stagnalis
Authors: Barnes Steven , Syed Naweed I. , Bulloch Andrew G. M. , Lukowiak Ken
Published: April 2021

Dopamine elicits alternating bursts of activity in the respiratory interneurones of the snail Lymnaea stagnalis. One of the neurones (VD4) was isolated in culture, and the effects of dopamine on both membrane voltage and current were studied utilising the whole-cell tight-seal recording technique. Dopamine had little effect on resting potentials near −60 mV, nor did it affect spike threshold or input resistance measured near −60 mV. However, it did alter the excitability of the cell, changing the response to current injection from one of repetitive spiking to one of rapid accommodation. Under voltage-clamp, VD4 responded to dopamine (EC50=92 nmol l−1) with increased net outward current at all potentials more positive than −60 mV. This was due primarily to an increase in voltage-gated potassium current and a decrease in calcium current. A reduction of Cd2+-sensitive outward current, possibly calcium-gated potassium current, was also evident at potentials more positive than +60 mV. The physiological actions of dopamine on these cells in vivo are consistent with the inhibitory mechanisms presented in this study.
Potential differences influence amino ACID/Na+ symport rates in larval Manduca sexta midgut brush-border membrane vesicles
Authors: Parthasarathy R. , Harvey William R.
Published: April 2021

The time-dependent fluorescence intensity of an intravesicular potential-sensitive dye was used to probe the real-time kinetics of potential difference (PD)-dependent amino acid/Na+ symport at pH 9 into brush-border membrane vesicles obtained from larval Manduca sexta midgut. Neutral amino acids (alanine, proline) are symported at higher rates as the vesicles are hyperpolarized. The symport rates of acidic (glutamate) and basic (arginine) amino acids are almost PD-independent. The half-saturation constant of alanine is PD-independent between −108 and −78 mV, although the maximal symport velocity increases by half as the voltage is increased. Amino acid throughput is evidently enhanced as the relatively high transmembrane PDs (>150 mV, lumen positive) measured in vivo are approached. The half-saturation concentrations of Na+ were in the range 15–40 mmol l−1 for most of the amino acids examined and increased with voltage for alanine. The Vmax observed as a function of cation or amino acid concentration increased as the vesicle was hyperpolarized in the case of leucine and alanine. The data support the hypothesis that carrier and substrates are at equilibrium inasmuch as substrate translocation seems to be the rate-determining step of symport.
The Localization of Phosphatase in Cells in Tissue Cultures
Authors: Willmer E. N.
Published: April 2021

In a recent paper, Gomori (1941) has described a histochemical method for the localization of phosphatase in animal tissues. The method depends on the fact that the enzyme is not destroyed by moderate treatment with 80 % alcohol, in which the tissues are fixed. After fixation the tissues are sectioned; the sections are incubated with sodium glycerophosphate and calcium chloride in buffered-solution and calcium phosphate is deposited at the site of phosphatase activity. This can be rendered visible by treatment with cobalt nitrate solution followed by ammonium sulphide, when the site of the phosphatase is marked by a black precipitate. By the use of such methods he has described, among other things, the occurrence of phosphatase in capillary endothelial cells in different animals, not with absolute regularity, but in a large number of cases. In those instances in which a positive reaction was not obtained it was shown to be an idiosyncrasy of the particular tissue rather than a failure of the method. It seemed possible therefore that an attempt to separate endothelial cells from other mesenchymal cells growing in vitro might be assisted by the use of this method.
The Rate of Regeneration of Nerve
Authors: Gutmann E. , Guttmann L. , Medawar P. B. , Young J. Z.
Published: April 2021

Five different methods have been used to estimate the rate of advance of regeneration along nerves in the rabbit. Not all give the same result. When the advance of the axon tips is studied a higher rate is recorded than when the times necessary for functional recovery are considered. In the latter case the experiment gives a measure of the rate of advance not of the tips of the axons but of completed nerve fibres, able to function. The ‘scar delay’, or period before arrival of new axon tips in the peripheral stump, is nearly constant in all well-made sutures (7·3 days). After interruption of a nerve by complete crushing at one spot this delay is only slightly shorter (5·2 days). There is a further delay before maturation to the level of functional completion begins to advance down the nerve, so that the total latent period before advance of recovery begins is about 36 days after suture and 20 days after crushing a nerve. The rate of advance of the fastest axon tips was determined by finding the furthest point from the lesion at which reflexes could be elicited by pinching the nerve. After suture of the n. peroneus in the rabbit this rate was 3·5 and after crushing 4·4 mm./day. This rate of the axon tips is not significantly different after crushing the nerve at different distances from the nerve cell body, namely high in the thigh or below the knee. This rate is similar in the tibial, peroneal and sural divisions of the sciatic in the rabbit. The rate of advance of functional completion of nerve fibres was measured by making lesions at various levels and studying (a) the time necessary for return of response to nociceptive stimuli to a given point on the skin and (b) the time for recovery of a given motor function, namely, spreading of the toes. Both methods give rates of 2·0 mm./day after suture, and 3·0 mm./day after crushing. Analgesic areas on the foot shrink at the rate of 2·1 mm./day during recovery after crushing the nerve, 1·6 mm./day after suture. Comparison of the times of recovery of muscles at varying distances from a lesion gives an estimate of rate of advance of functional completion of 2·2 mm./day after crushing a nerve, but this method is only approximate in the rabbit. In rabbits of 1 month old the rate of advance of the axon tips is not greatly different from that in adults, but the delay in the scar is less, and maturation of the nerve fibres proceeds more rapidly.
Neural Induction in Epidermal Explants in Liquid Medium
Authors: Shen S. C.
Published: April 2021

In previous communications (Waddington, 1938; Shen, 1939), it has been shown that a water-soluble derivative of a carcinogenic hydrocarbon is a potent neuralizing agent when implanted with the coagulum of egg albumen into a young gastrula. The present paper describes a similar study with the following modifications: (1) pieces of completely isolated presumptive epidermis were used instead of the whole gastrulae; and (2) the evocatory substance, Na-1:2:5:6-dibenzan-thracene-α-β-endo-succinate, was not tested in the form of a solid implant in admixture with the coagulum of ovoalbumen, but as a solute dissolved in a neutral salt solution in which the epidermal explants were cultivated.
The Storage of Protein, Fat, Glycogen and Uric Acid in the Fat Body and Other Tissues of Mosquito Larvae
Authors: Wigglesworth V. B.
Published: April 2021

It is generally agreed that the main function of the fat body of insects is the storage of those reserve substances which require rapid mobilization during moulting and metamorphosis. But little attention has been given to the part taken by other organs and tissues in building up reserves and almost none to the influence of the composition of the food upon the type of reserve substance laid down.
Observations on the Distribution of Ascorbic Acid (Vitamin C) in Explanted Cells
Authors: Barnett S. A.
Published: April 2021

A Survey was recently made of the distribution of ascorbic acid in the embryonic tissues of the chick (Barnett & Bourne, 1941, 1942). Its results raised a number of. problems which can only be solved experimentally. A study was therefore under-taken of ascorbic acid in cultured tissues from chick embryos. Owing to the war this work could not be completed, but it is considered desirable to record the few observations which have been made.
Diurnal Fluctuations of Oxygen and pH In Two Small Ponds and A Stream
Authors: Whitney R. J.
Published: April 2021

There are few available data on diurnal changes in chemical and physical factors in fresh-water environments. Morren & Morren (1841) are credited with the first observation of a diurnal fluctuation in dissolved oxygen.
Some Developmental Effects of X-Rays in Drosophila
Authors: Waddington C. H.
Published: April 2021

If Drosophila larvae homozygous for the third chromosome recessive straw-3 are treated with X-rays, back-mutations of the straw-3, gene to its normal allelomorphs take place in somatic cells, and the cells of the wings give rise to hairs which can be recognized as wild type (Waddington, 1940b). In one attempt to follow out this matter in more detail high doses (7000 r. units) were applied. The resulting mortality was, it might be said, 100 %. That is, no flies emerged; but on dissecting the pupa cases, it was found that a considerable proportion had developed up to the hatching stage, but had not been able to free themselves from the pupal integuments. These flies were found to exhibit some rather remarkable deformities, and the experiment has therefore been repeated a number of times. It is the purpose of the present paper to describe in some detail the developmental abnormalities produced by such heavy doses of X-rays. Friesen (1936) originally described some abnormalities (which he termed ‘Roentgenmorphoses’) produced by slightly smaller doses, and some further notes on such cases have been published by Enzmann & Haskins (1938a, b) and Haskins & Enzmann (1937). All the abnormalities found by these authors can probably be considered as due to inhibitory actions of X-rays on various developmental processes; but, as will be clear later, the striking feature of the animals to be discussed in the present communication is that in some of them the growth of certain rudiments has been actually stimulated by the radiation. A preliminary communication of the experiments recorded in this paper has been published (Waddington, 1942).
Studies On the Physiology of Arenicola Marina L.
Authors: Wells G. P. , Ledingham I. C.
Published: April 2021

The ‘isolated extrovert’ of the lugworm consists of the proboscis with a short length of oesophagus attached. It remains active for over 24 hr. in sea water and gives a remarkable rhythmic pattern consisting of outbursts of vigorous activity alternating with periods of relative rest (Wells, 1937). We have already published its reactions to changes in osmotic pressure and magnesium concentration (Wells & Ledingham, 1940a, b). We now continue our study of its relations with its bathing medium by describing the effects of varying the potassium concentration. As many authors have found that potassium: magnesium antagonism is important in invertebrate preparations, and as the extrovert behaves normally in a fluid whose magnesium content is high, we have paid particular attention to the possibility of antagonism between the two ions in the present case.
Quantitative Aspects of the Disk-Sphere Transformation Produced by Lecithin
Authors: Ponder Eric
Published: April 2021

This paper is concerned with quantitative aspects of the disk-sphere transformation of the mammalian red cell produced by lecithin (Ponder, 1935 a). This shape transformation, brought about when lecithin is added to mammalian red cells in saline or in plasma, and reversed by washing off the lecithin or by adding an excess of plasma, is very suitable for quantitative study, since, unlike the shape transformations produced by rose bengal and other lysins, it is not soon followed by haemolysis. Exact work on the factors involved, however, has been very difficult, for two reasons. (1) An unrelated disk-sphere transformation occurs when red cells in saline, whether lecithin-treated or not, are placed between a slide and a closely applied cover-glass (Ponder, 1929), and so it has not been possible to examine the lecithin shape transformation of the cells in saline except in uncovered preparations or in hanging drops. Even under these circumstances, the two factors responsible for the slide-slip transformation, removal of anti-sphering substance by the glass and diffusion of alkali from the glass (Furchgott, 1940; Furchgott & Ponder, 1940) interfere with the observations. This difficulty can now be avoided by using plastic slides and cover-slips, between which these interfering phenomena do not occur. (2) The original method of adding lecithin to plasma or saline by mechanical emulsification is not satisfactory, as the amount of lipoid emulsified is usually unknown and its physical state is variable. Recently I have used sols of lecithin in saline, in which the dispersion approaches uniformity and a known quantity of lipoid is present.
The Mechanism of the Nervous Regulation of the Crayfish Heart
Authors: Wiersma C. A. G. , Novitski E.
Published: April 2021

A preparation is described in which the peripheral inhibitor and accelerator nerves of the crayfish (Cambarus clarkii) heart can be separately or simultaneously stimulated. The effect of different frequencies of stimulation were investigated; complete stoppage of the heart was obtained only with rather high frequencies (45 per sec.); maximal acceleration, with lower frequencies (30 per sec.). No difference in effects between left and right nerves was found. Perfusion with acetylcholine and stimulation of the accelerator nerve produce identical effects. Perfusion with eserin does not influence the normal heart beat but enhances the effect of acceleration.

The nerve of Lemoine has no regulatory influence on the heart.

Special inhibitory and acceleratory tracts have been prepared in the suboesophageal commissures. Each of these tracts makes heterolateral as well as homolateral connexions. The influence of the frequency of stimulation on the central tracts has been studied.

An hypothesis with regard to the mechanism of the crayfish heart beat and its control is presented.
Observations On the Forces of Morphogenesis in the Amphibian Embryo
Authors: Waddington C. H.
Published: April 2021

The cells of early amphibian embryos contain ellipsoidal yolk granules. When a granule lies within the mitotic spindle, it is orientated with its long axis parallel to the direction ofthe spindle fibres. Yolk granules lying in the cytoplasm of cells are not specially orientated unless they lie in narrow spaces between cell surfaces; this is true in cells of the moving invagination streams, in the flask cells of the young blastopore, and in elongated cells of the neural groove and lens. The breaking strain of cell surfaces was tested by bringing the cells into surfaces of known strength and observing whether they withstood the applied tension. The evidence indicates: (a) That the breaking strain of cells from gastrula and tail-bud embryos is some tens of dynes per centimetre.(b) That the breaking strain is not the same in all cells, being highest in neural tissue and lowest in endoderm during the stages mentioned.(c) That the breaking strain gradually increases with age.(d) That in the neural groove stage the strength of the outer concave surface of the groove is greater than that of the inner convex surface. It is suggested that changes in surface tensions may be of importance in bringing about morphogenesis. The possibility is envisaged that the changes in tension may be connected with orientated fibrizations of the surface proteins.
Acquisition of magnetic directional preference in hatchling loggerhead sea turtles
Authors: Lohmann Kenneth J. , Fittinghoff Lohmann Catherine M.
Published: April 2021

During their natal migration, hatchling loggerhead sea turtles (Caretta caretta L.) establish courses towards the open ocean and maintain them after swimming beyond sight of land. Laboratory experiments have demonstrated that swimming hatchlings can orient using the earth’s magnetic field. For the magnetic compass to function in guiding the offshore migration, however, hatchlings must inherit or acquire a magnetic directional preference that reliably leads them towards the open sea.

On land, hatchlings find the ocean using light cues associated with the seaward horizon. To determine whether turtles might acquire a preference for a specific magnetic direction on the basis of such cues, we studied the magnetic orientation of turtles initially exposed to light from either magnetic east or west. Hatchlings that had been exposed to light in the east subsequently oriented eastward when tested in darkness, whereas those that had been exposed to light in the west swam westward. Reversing the magnetic field resulted in a corresponding shift in orientation, indicating that the turtles were orienting to the ambient magnetic field.

These results demonstrate that light cues can set the preferred direction of magnetic orientation by loggerhead hatchlings. We therefore hypothesize that hatchlings initially establish a seaward course using visual cues available on or near land, then maintain the course using magnetic cues as they migrate into the open sea.
Extracellular ATP can activate autonomic signal transduction pathways in cultured equine sweat gland epithelial cells
Authors: Ko Wing Hung , O’Dowd John J. M. , Pediani John D. , Bovell Douglas L. , Elder Hugh Y. , Jenkinson David McEwan , Wilson Stuart M.
Published: April 2021

Changes in intracellular free calcium concentration ([Ca2+]i) were monitored in a cell line that was derived from the equine sweat gland epithelium. ATP and closely related compounds could increase [Ca2+]i with a rank order of potency of UTP⩾ATP⪢ADPAMP=adenosine=α,β-methylene-ATP. The responses to ATP and to UTP were initiated by the release of calcium from an internal store and subsequently sustained by calcium influx. The rise in [Ca2+]i thus seems to be mediated by P2U receptors that are coupled to phosphoinositidase C. Some desensitisation of this response developed during repeated stimulation with ATP and this was blocked by staurosporine, an inhibitor of protein kinase C, and augmented by a phorbol ester which acts as an exogenous activator of this enzyme. A protein-kinase-C-dependent inhibitory pathway thus seems to become active during repeated stimulation with ATP. ATP and related compounds could also raise cellular cyclic AMP content. The order of potency was ATP>ADP⪢AMP=adenosineUTP, suggesting that this response is mediated via a separate subclass of P2 receptor. The present results demonstrate that ATP can activate autonomic signal-transduction pathways in cultured equine sweat gland cells and suggest that there may be a purinergic component to the control of secretory activity in the equine sweat gland.
Multiple receptors mediate the modulatory effects of serotonergic neurons in a small neural network
Authors: Zhang Bing , Harris-Warrick Ronald M.
Published: April 2021

The gastropyloric receptor (GPR) cells are a set of cholinergic/serotonergic mechanosensory neurons that modulate the activity of neural networks in the crab stomatogastric ganglion (STG). Stimulation of these cells evokes a variety of slow modulatory responses in different STG neurons that are mimicked by exogenously applied serotonin (5-HT); these responses include tonic inhibition, tonic excitation and induction of rhythmic bursting. We used pharmacological agonists and antagonists to show that these three classes of modulatory response in the STG neurons are mediated by distinct 5-HT receptor subtypes. GPR stimulation or application of 5-HT or 2-me-5HT (a vertebrate 5-HT3 agonist) inhibited the pyloric constrictor (PY) neurons; these actions were selectively antagonized by gramine. GPR stimulation or application of 5-HT induced rhythmic bursting in the electrically coupled anterior burster (AB) and pyloric dilator (PD) neurons; these effects were antagonized by the 5-HT1c/2 antagonist cinanserin and by atropine at concentrations that do not block muscarinic cholinergic receptors in the crab STG. The 5-HT agonists 5-CT (5-HT1 ) and α-me-5HT (5-HT2 ) also induced AB/PD bursting, which was blocked by cinanserin, but not by atropine. GPR stimulation or application of 5-HT and 5-CT evoked tonic excitation of the lateral pyloric (LP) neuron. These effects were blocked by cinanserin. Several other 5-HT agonists and nearly all the vertebrate 5-HT antagonists we tested had little or no effect on the crab pyloric 5-HT receptors. These results provide further evidence that the modulatory sensory GPR neuron uses serotonin to evoke multiple modulatory responses via multiple 5-HT receptors. However, the 5-HT receptors in the crab STG neurons are not pharmacologically similar to vertebrate 5-HT receptors.
A Microcalorimetric Study of Turtle Cortical Slices: Insights Into Brain Metabolic Depression
Authors: Doll Christopher J. , Hochachka Peter W. , Hand Steven C.
Published: April 2021

In previous papers, we have examined turtle cortical neurons in vitro for mechanisms of anoxic metabolic depression (‘channel arrest’ and changes in electrical parameters). Negative results prompted the current study with the aim of examining more closely the energy profile and metabolism of turtle cortical slices. Calorimetry is used to measure heat dissipation during normoxia and nitrogen perfusion (120 min) and the results are converted into an ATP utilization rate. These indicate that the control rate of ATP utilization (1.72 μmol ATP g−1 min−1) agrees closely with in vivo whole-brain metabolic measurements. Both nitrogen perfusion and pharmacologically induced anoxic (cyanide+N2) groups depressed heat dissipation considerably compared with the control value (nitrogen 37%; pharmacological anoxia 49%). The resulting ATP utilization estimates indicate metabolic depressions of 30% (nitrogen) and 42% (pharmacological anoxia). The slice preparation did not exhibit a change in any measured adenylate parameter for up to 120 min of anoxia or pharmacological anoxia. Significant changes did occur in [ADP], ATP/ADP ratio and energy charge after 240 min of exposure to anoxic conditions. These results support the idea that the turtle cortical slice preparation has a profound resistance to anoxia, with both nitrogen perfusion and pharmacological anoxia causing a rapid decline in heat dissipation and metabolism.
Cardiovascular Responses to Scyliorhinin I and II in the Rainbow Trout, Oncorhynchus Mykiss, in Vivo and In Vitro
Authors: Kågström Jens , Axelsson Michael , Holmgren Susanne
Published: April 2021

Changes in cardiac output, heart rate, dorsal aortic blood pressure and coeliac artery blood flow were measured in unrestrained rainbow trout, Oncorhynchus mykiss, following injections of the elasmobranch tachykinins scyliorhinin I and II. The resistance in the coeliac vascular bed and the total systemic vasculature were calculated from blood pressure and flow. In addition, isolated tails were perfused to investigate the effect of the peptides on the somatic vasculature. Scyliorhinin I (SCY I) produced a biphasic change in the coeliac vascular resistance: an initial decrease was followed by an increase. The decrease in coeliac vascular resistance was accompanied by a decrease in the total systemic vascular resistance, leading to an increased cardiac output. The ensuing increase in coeliac vascular resistance caused a slight increase in blood pressure. In the perfused tail, SCY I produced a marked increase in the somatic vascular resistance. Scyliorhinin II (SCY II) decreased the systemic vascular resistance, causing an increase in cardiac output. SCY II also caused a late increase in the coeliac vascular resistance, which led to hypertension and bradycardia. In vitro, SCY II produced a biphasic response in which an initial decrease in the somatic resistance was followed by a larger increase. The results demonstrate that exogenous SCY I and II are vasoactive peptides that act by different mechanisms in the rainbow trout cardiovascular system. Their actions also differ from the actions of substance P previously observed in the cod, Gadus morhua, and possibly involve a neural reflex.
Variations in Force–Time Histories of cat Gastrocnemius, Soleus and Plantaris Muscles for Consecutive Walking Steps
Authors: Herzog W. , Zatsiorsky V. , Prilutsky B. I. , Leonard T. R.
Published: April 2021

Force-sharing among muscles during locomotion has been studied experimentally using ‘representative’ or ‘average’ step cycles. Mathematical approaches aimed at predicting individual muscle forces during locomotion are based on the assumption that force-sharing among muscles occurs in a consistent and unique way. In this study, we quantify normal variations in muscular force–time histories for step cycles executed at a given nominal speed, so that we can appreciate what it means to analyze ‘representative’ or ‘average’ step cycles and can evaluate whether these normal variations in muscular force–time histories are random or may be associated with variations in the kinematics of consecutive step cycles. Forces in gastrocnemius, soleus and plantaris muscles were measured for step cycles performed at a constant nominal speed in freely moving cats. Gastrocnemius forces were always larger than peak plantaris or soleus forces. Also, peak gastrocnemius forces typically occurred first after paw contact, followed by peak soleus and then peak plantaris forces. Furthermore, it was found that variations in muscular force–time histories were substantial and were systematically related to step-cycle durations. The results of this study suggest that findings based on ‘representative’ or ‘average’ step cycles for a given nominal speed of locomotion should be viewed cautiously and that variations in force-sharing among muscles are systematically related to variations in locomotor kinematics.
Ammonia Excretion in Freshwater Rainbow Trout (Oncorhynchus Mykiss) and the Importance of Gill Boundary Layer Acidification: Lack of Evidence for Na+/NH4+ Exchange
Authors: Wilson Rod W. , Wright Pam M. , Munger Steve , Wood Chris M.
Published: April 2021

Net ammonia fluxes (JAmm) were measured in adult freshwater rainbow trout in vivo under a variety of conditions designed to inhibit unidirectional sodium uptake (; low external [NaCl], 10−4 mol l−1 amiloride), alter transbranchial and NH4+ gradients [24 h continuous (NH4)2SO4 infusion, or exposure to 1 mmol l−1 external total ammonia at pH 8] and prevent gill boundary layer acidification (5 mmol l−1 Hepes buffer). Inhibition of with amiloride or low external [NaCl] under normal conditions reduced JAmm by about 20%, but did not prevent the net excretion of ammonia during exposure to high concentrations of external ammonia. Increasing the buffer capacity of the ventilatory water with Hepes buffer (pH 8) reduced JAmm by 36% and abolished the effect of amiloride on ammonia excretion.

No evidence could be found to support a directly coupled apical Na+/NH4+ exchange. We suggest that any dependence of ammonia excretion on sodium uptake is caused by alteration of transbranchial gradients within the gill microenvironment secondary to changes in net H+ excretion. Under normal conditions (pH 8, low external ammonia) gill boundary layer acidification facilitates over one-third of the total ammonia excretion. During exposure to high concentrations of external ammonia in poorly buffered water, estimates of transbranchial gradients from measurements of bulk water pH and total ammonia concentration (TAmm) may be grossly in error because of boundary layer acidification. Prevention of boundary layer acidification with Hepes buffer during exposure to high cocncentrations of external ammonia revealed that the local transbranchial gradient at the gill may in fact be positive (blood to water), negating the need for an active NH4+ transport mechanism. In freshwater trout, NH3 diffusion may account for all ammonia excretion under all experimental conditions used in the present study.
Morphological Changes and Functional Recovery Following Axotomy of a Serotonergic Cerebrobuccal Neurone in the Land Snail Achatina Fulica
Authors: Chiasson Bernard J. , Baker Michael W. , Croll Roger P.
Published: April 2021

We have examined an identified serotonergic neurone in Achatina fulica and described the normal morphological and physiological characteristics of this cell. Injury-induced changes in this neurone following in vivo recovery are described and compared with in vitro gastropod models of regeneration. Nickel–lysine and biocytin dye-fills of the metacerebral giant (MCG) neurone, together with serotonin-like immunoreactivity, revealed an extensive innervation of the ipsilateral buccal ganglion, much greater than that previously reported. Labelled MCG fibres were seen to ramify throughout the ganglion, providing extensive neuropilar innervation. Serotonin-immunoreactive fibres were seen not only within the neuropile but also within the cell body layer of the buccal ganglia, surrounding many of the cell bodies with varicose fibres. Dye-fills also revealed a minor contralateral buccal innervation not previously described. This view of a predominantly ipsilateral innervation of the buccal ganglia by the MCG was supported by electrophysiological measurements. The ipsilateral buccal follower cell B1 displayed an increase in depolarization in response to repeated trains of action potentials to the MCG, whereas the contralateral B1 showed only a weak depolarization in response to the identical stimuli.

Following a crush to the cerebral–buccal connective (CBC), the MCG rapidly regenerated its injured projections, displaying both morphological and physiological recovery within 5–10 days. The original, severed fibres of the MCG were, however, replaced by a multitude of smaller neurites, which persisted for up to 3 months (the longest recovery period examined). Despite this morphological difference between normal and regenerated fibres, the MCG re-established functionally equivalent connections upon B1. In contrast with previous in vitro studies using gastropods, serotonin-like immunoreactivity revealed that severed distal fibres from the MCG rapidly degenerated (2–6 days), resulting in a transient unilateral depletion of serotonin in the buccal ganglia. We suggest that this loss of serotonin in the lesioned ganglion may play a functional role in regeneration, as has been suggested in vitro.
Structural Basis for Wavelength Discrimination in the Banked Retina of the Firefly Squid Watasenia Scintillans
Authors: Michinomae Masanao , Masuda Hiroko , Seidou Masatsugu , Kito Yuji
Published: April 2021

There is a greatly thickened region of retina in the ventral part of the eye of the firefly squid Watasenia scintillans, with an outer segment (OS) layer around 600 μm thick. The distal two-thirds of this OS layer is yellow and contains a visual pigment, based on 4-hydroxyretinal (A4), with an absorbance maximum at 470nm. The proximal third is pink and contains a visual pigment, based on dehydroretinal (A2), with an absorbance maximum at 500nm. Light and electron microscopic investigations demonstrate the presence of four types of photoreceptor cell. In the pink layer, three of the four types (α, β and γ) produce no microvilli and are columnar in structure. These cells form square microvillous rhabdoms only in the distal yellow layer. The fourth cell type (δ) produces microvilli in the pink layer only. These observations led us to propose that the A2-based visual pigment is contained in the pink-layer cells and that the A4-based visual pigment is contained in the three types of yellow-layer cells. The absorbance of fresh retina was determined by microspectrophotometry. The yellow OS layer, with an absorbance of 0.7 per 100 μm thickness at 470nm, is expected to act as a short-wavelength cut-off filter to the underlying pink OS cells, shifting their photosensitivity peak by an estimated 50nm to 550nm. Possible wavelength discrimination by this squid is discussed.
Activity of Giant Interneurones and Other Wind-Sensitive Elements of the Terminal Ganglion in the Walking Cricket
Authors: Kohstall-Schnell Dorothea , Gras Heribert
Published: April 2021

Using intracellular recording techniques in stationary walking crickets (Gryllus bimaculatus), we have investigated the relationship between locomotion and the activity of interneurones ascending from the terminal ganglion. Nine different types of giant interneurones (GI) were characterized during walking and standing. One third of them reduced their activity, while the others enhanced their spike rate, during walking. These physiological properties were strictly correlated with morphological characteristics such as axon position in the longitudinal tracts of the terminal ganglion. In general, ventral GIs reduced and dorsal GIs increased their spike frequency during walking. In some of them, there was a weak but significant correlation between the spike rate and translational speed, but no correlation with rotational speed.

In all GIs except 10-3a, the changes in activity occurred at the start of walking. In GI 10-3a, an increase in membrane potential and spike rate was observed before the start of locomotion. Therefore, an intrinsic mechanism within the central nervous system operating on GI 10-3a is suggested.

Additionally, the activities of filiform hair receptors and of previously undescribed small ascending interneurones (SAI) have been studied during walking. About 80% of the receptors slightly increased their spike rate during walking, while one SAI became more active during walking and another one was hardly affected.

The physiological properties of ascending interneurones are discussed with respect to their modulation and particular function during walking.
Efficiency of Fast- and Slow-Twitch Muscles of the Mouse Performing Cyclic Contractions
Authors: Barclay C. J.
Published: April 2021

The mechanical efficiency of mouse fast- and slow-twitch muscle was determined during contractions involving sinusoidal length changes. Measurements were made of muscle length, force production and initial heat output from bundles of muscle fibres in vitro at 31°C. Power output was calculated as the product of the net work output per sinusoidal length cycle and the cycle frequency. The initial mechanical efficiency was defined as power output/(rate of initial heat production + power output). Both power output and rate of initial heat production were averaged over a full cycle of length change. The amplitude of length changes was ±5% of muscle length. Stimulus phase and duration were adjusted to maximise net work output at each cycle frequency used. The maximum initial mechanical efficiency of slow-twitch soleus muscle was 0.52±0.01 (mean ±1 S.E.M. N=4) and occurred at a cycle frequency of 3 Hz. Efficiency was not significantly different from this at cycle frequencies of 1.5–4 Hz, but was significantly lower at cycle frequencies of 0.5 and 1 Hz. The maximum efficiency of fast-twitch extensor digitorum longus muscle was 0.34±0.03 (N=4) and was relatively constant (0.32–0.34) over a broad range of frequencies (4–12 Hz). A comparison of these results with those from previous studies of the mechanical efficiency of mammalian muscles indicates that efficiency depends markedly on contraction protocol.
Acid–Base Regulation, Branchial Transfers and Renal Output in a Marine Teleost Fish (The Long-Horned Sculpin Myoxocephalus Octodecimspinosus) During Exposure to low Salinities
Authors: Claiborne James B. , Walton Julie S. , Compton-McCullough Dana
Published: April 2021

A number of studies have implied a linkage between acid–base and ion exchanges in both freshwater and seawater fish, although little is known about the branchial and renal acid–base transfers involved as the animals move between different salinities. To investigate the role of these transfers in a marine teleost fish as it is exposed to a dilute environment, we measured plasma acid–base values and net movements from fish to water of NH4+, HCO3− and H+ in long-horned sculpin (Myoxocephalus octodecimspinosus) placed in 100%, 20%, 8% or 4% sea water for 24–48h. Renal excretion of H+ was also monitored in fish exposed to 4% sea water. Sculpin proved to be somewhat euryhaline for they were able to maintain plasma ion and acid–base transfers in hypo-osmotic (20%) sea water, but could not tolerate greater dilutions for more than several days. Plasma pH and carbon dioxide concentration increased in the 20% and 8% dilution groups, with nearly doubling (control, 4.56mmol l−1; 8% group, 8.56mmol l−1) as a result of a combined increase in the partial pressure of plasma CO2 and [HCO3−]. During a 44–46h exposure, HCO3− transfers increased progressively in the most dilute water, with animals in the 8% and 4% groups exhibiting a net H+ loss that was smaller than that of seawater fish (control, 5.1mmolkg−1; 8%, 0.9mmolkg−1; 4%, -2.9mmolkg−1). Animals exposed to 4% sea water for 24h and then returned to normal sea water had a variable plasma pH, an elevated and a net efflux of H+ that effectively stopped (control, 0.10mmolkg−1 h−1; 4%, 0.02mmolkg−1 h−1; seawater recovery, 0.20mmolkg−1 h−1) during the low-salinity period. Renal acid excretion remained relatively constant throughout the experiment but only made up a significant portion (approximately 40%) of the total acid transfers during the 4% dilution period (control rate approximately 3 µmolkg−1 h−1: 3% of branchial rate).

We postulate that the increase in plasma during exposure to low salinity may be due to mobilization of base from the intracellular bone compartment. The decrease in external salinity could induce base loss by alteration of gill ion exchanges (Na+/H+, Cl−/HCO3−) and/or changes in branchial HCO3− permeability. For the first time, we have shown that the effects of a dilute environment on acid–base transfers may be an important limitation to the survival of a euryhaline species in brackish or fresh water.
Unique Permeability Barrier of the Apical Surface of Parietal and Chief Cells in Isolated Perfused Gastric Glands
Authors: Boron Walter F. , Waisbren Steven J. , Modlin Irvin M. , Geibel John P.
Published: April 2021

Although many factors can influence intracellular pH (pHi), some of the most important are those that involve the movement of acids and bases across the cell membrane. We will discuss recent results concerning barriers to the movement of H+, NH3 and CO2 across the apical cell membranes of gastric gland cells. Cell membranes are generally highly permeable to small, lipophilic molecules such as NH3 and CO2. In fact, only two examples are known of membranes relatively impermeable to NH3 and none of membranes permeable to CO2. We recently developed a technique for perfusing the lumen of a single hand-dissected gastric gland on the stage of a microscope, while monitoring pHi with a fluorescent dye. We observed the expected pHi changes when we exposed the basolateral (i.e. blood-side) membrane to a pH 6.4 solution (a large, rapid pHi decrease), to a pH 7.4 solution containing approximately 0.3 mmol l−1 NH3 (a large and rapid pHi increase) or to a pH 7.4 solution equilibrated with 1% CO2 (a rapid pHi decrease of -0.08). However, pHi was not significantly affected by perfusing the lumen with a pH 1.4 solution, with a pH 7.4 solution containing as much as 2.7 mmol l−1 NH3 or with a pH 6.1 solution equilibrated with 100% CO2. These data indicate that a barrier at or near the apical membrane has a uniquely low permeability to H+, NH3 and CO2.
Na+/H+ Antiport: Modulation by Atp and Role in Cell Volume Regulation
Authors: Demaurex Nicolas , Grinstein Sergio
Published: April 2021

Na+/H+ antiport is a major determinant of intracellular pH (pHi) and also plays an important role in the maintenance of cellular volume. Na+/H+ exchange through NHE-1, the ubiquitous isoform of the antiporter, is accelerated by cytosolic acidification and also by osmotically induced cell shrinking, thereby promoting recovery of the physiological pHi and volume, respectively. Although hydrolysis of ATP is not required for transport of ions through the antiporter, metabolic depletion exerts a marked inhibitory effect. Depletion of ATP also prevents osmotic activation and volume regulation. Contrary to earlier suggestions, however, changes in the phosphorylation state of the antiporter itself are not involved in the effects of either metabolic depletion or osmotic stimulation. Nevertheless, the cytosolic carboxy-terminal segment of the antiporter, which contains the major phosphorylation sites, is essential for the ATP dependence as well as for osmotic activation. It is conceivable that this domain interacts with ancillary phosphorylated or nucleotide-binding proteins, with the cytoskeleton and/or with specific phospholipids, which modulate the rate of transport.

Nucleotide dependence and osmotic sensitivity have been compared in three different isoforms of the antiporter, heterologously expressed in fibroblastic cells. Like NHE-1, NHE-2 and NHE-3 were severely inhibited by depletion of ATP. In contrast, whereas NHE-2 was stimulated by osmotic shrinkage, NHE-3 was inhibited. The possible physiological significance of the ATP-dependence and osmotic responsiveness of the antiporter isoforms is discussed.
Bacterial and Plant Antiporters
Authors: Maloney Peter C.
Published: April 2021

Articles in this chapter emphasize the phenomenon of ion exchange across biomembranes. This topic has been of interest at least since 1947, when Hans Ussing articulated his model of ‘exchange diffusion’ to account for an unexpected elevation in the rate of 22Na+ efflux from skeletal muscle (Ussing, 1947). Ussing had tried to measure net Na+ movement by following tracer flux, but found that this approach greatly overestimated the true value. To explain this overestimate, Ussing postulated that isotopic flux reflected only isotopic exchange rather than net movement of mass, and he proposed the following model. Perhaps a negatively charged carboxyl group on some membrane element accepts the positively charged 22Na+ so that the neutral complex can move through the membrane (mechanism unspecified) without interference from the electric field? If so, at the opposite surface, tracer could be discharged, replaced by (non-radioactive) 23Na+, and the neutral complex would return to the original membrane surface, and at that point 23Na+ would be released to let the cycle begin again. Clearly, by following the movement of 22Na+, one might considerably overestimate the true net movement of Na+ itself.
The Role of Monovalent Cation/Proton Antiporters in Na+-Resistance and pH Homeostasis in Bacillus: An Alkaliphile Versus A Neutralophile
Authors: Krulwich Terry Ann , Cheng Jianbo , Guffanti Arthur A.
Published: April 2021

Both neutralophilic Bacillus subtilis and alkaliphilic Bacillus firmus OF4 depend upon electrogenic Na+/H+ antiporters, which are energized by the gradients established by respiration-coupled proton extrusion, to achieve Na+-resistance and pH homeostasis when the external pH is very alkaline. The interplay of proton and sodium cycles is discussed. In B. subtilis, pH homeostasis, up to pH 9, can be achieved using K+ when Na+ is unavailable or when the gene encoding the Na+/H+ antiporter that is involved in Na+-dependent pH homeostasis is disrupted. That gene is a member of the tetracycline efflux family of genes. A second gene, encoding a Na+/H+ antiporter that functions in Na+-resistance, has been identified, and candidates for the K+/H+ antiporter genes are under investigation. Aggregate Na+/H+ antiport activity in B. subtilis is as much as 10 times lower than in the alkaliphile, and the neutralophile cannot regulate its internal pH upon a shift to pH 10.5. Upon such a shift, there is a pronounced reduction in the generation of a primary electrochemical proton gradient. The alkaliphile, by contrast, maintains substantial driving forces and regulates its internal pH in an exclusively Na+-coupled manner upon shifts to either pH 8.7 or 10.5. One gene locus has been identified and a second locus has been inferred as encoding relevant antiporter activities.
Uniporters, Symporters and Antiporters
Authors: Wolfersberger Michael G.
Published: April 2021

Transporters are a diverse group of membrane proteins that facilitate the movement of water-soluble solutes through the lipid bilayer of biological membranes. The least complex transporters are the uniporters (Kakuda and MacLeod, 1994). They simply facilitate the diffusion of their substrates across membranes and dissipate substrate gradients that arise as the result of other processes. Uniporters fall into two classes, channels and carriers, which mediate transmembrane solute movement by fundamentally different mechanisms. Channel proteins contain hydrophilic pores that span the lipid bilayer. Water-soluble solutes move across the membrane by diffusion through these pores. The lumen of a channel is accessible from either side of the membrane simultaneously. Carriers may also span the lipid bilayer, but their substrate binding sites are never accessible from both sides of the membrane simultaneously. Because of this difference in mechanism, carriers but not channels are able to mediate countertransport (Harold, 1986). Since carriers are much more closely related, at least mechanistically, to symporters and antiporters than to channels, they are the type of uniporter emphasized in this volume.