Ultrastructure of the osphradium of Aplysia californica

Summary The osphradium of Aplysia californica, a sensory organ, is a small yellow-brown epithelial patch located in the mantle cavity immediately anterior to the rostral attachment of the gill. Scanning electron microscopy reveals a round ellipsoid structure of 0.6–1 mm in diameter with a central, occasionally folded, sensory epithelium. The central area is covered with microvilli and surrounded by a densely ciliated epithelium. Transmission electron micrographs show that the columnar supporting cells in the sensory epithelium contain an abundance of apical pigment granules and microvilli. Between the epithelial-supporting cells, the putative sensory elements consist of thin neurites (0.4–1.5 m in diameter) that reach the sea-water side of the osphradium. The neurites contain many neurotubules, mitochondria, vesicles and cilia in their apices. The nerve endings originate from cell bodies up to 40 m below the epithelium or in the osphradial ganglion itself, as revealed by electron microscopy and retrograde labeling with Lucifer yellow. There appear to be two populations of putative sensory cells, a large population of heavily stained cell bodies 4–10 m in diameter and a few scattered cells of large diameter (25–60 m). Following lanthanum impregnation, septate junctions can be seen between all types of cells in the epithelium, 3–5 m below the sea-water surface. This study provides new information for further investigation of osmo- and mechanosensation in Aplysia californica.     

Increased prolactin binding and morphological changes in the wound epithelium of regenerating limbs of Notophthalmus viridescens

Summary Distribution of prolactin has been examined in regenerating forelimbs from the newt Notophthalmus viridescens. Specific prolactin binding was demonstrated in homogenates of unamputated tissue, and of regenerating limbs at from 3 to 21 days postamputation. Labeled prolactin that was injected intraperitoneally into animals with one regenerating limb accumulated in the most distal portion of the regenerate at 7 and 14 days postamputation. Light microscopic autoradiography demonstrated that labeled prolactin was localized most heavily in the apical, outer layer of the wound epithelium. Scanning electron microscopy demonstrated that, in addition to changes in prolactin affinity following amputation, morphological changes occurred in the apical wound epithelium as well. Cell surfaces of the stump epidermis were characterized by periodic dispersion of papillae among a network of interconnecting structures 1–2 m across. By contrast, the surfaces of cells from the area in which labeled prolactin was found to localize most intensely were characterized by lack of papillae and, depending on the stage of regeneration, a pattern of microvilli and microplicae. These morphological alterations appear to reflect functional and biochemical differences between stump epidermis and wound epithelium.     

Morphology of the Respiratory Trees in the Holothurians Apostichopus japonicus and Cucumaria japonica

The morphology of the respiratory trees in the holothurians Apostichopus japonicus and Cucumaria japonica was studied using histochemical and electron microscopic techniques. The epithelium of the respiratory tree cavity in A. japonicus consists of columnar cells about 17–20 m high. In C. japonica, this epithelium is composed of two cell types: bulbous cells embedded in the connective tissue layer and secretory cells; cells are 1–12 m high. A characteristic feature of cells of the respiratory tree cavity epithelium in these species is the presence of numerous phagosomes and coated vesicles in the apical cytoplasm. The cell surface has many microvilli and a single cilium. Cells of the coelomic epithelium contain vacuoles in the apical part and myofibrils in the basal region; the thickness of this epithelium in A. japonicus and C. japonica is 9–16 and 10–30 m, respectively. Based on the different structure of the respiratory trees and the absence of hemocytes in A. japonicus, it is suggested that the holothurian species studied have different routes of oxygen transport from the environment to the internal organs.     

Adaptations for reproduction and development in the skin-brooding ghost pipefishes,Solenostomus

Synopsis Ghost pipefishes comprise a small family (Solenostomidae) of skin-brooding fishes related to true pipefishes and seahorses (Syngnathidae).Solenostomus embryos develop within the fused pelvic fins of the female, unlike syngnathids in which males brood the eggs. Embryos, enclosed in egg envelopes, are attached to epidermal stalks, termed cotylephores, that occur only in brooding females. Cotylephores are cellular outgrowths of the epithelium on the inside surface of the pelvic fins. They attain a mean length of 687 ± 3.89 m and diameter of 105 ± 3.38 m. Cotylephores originate on the epithelial surface that lies over the lepidotrichia and they develop into multi-headed cylindrical branches approximately 125 ± 3.65 m in length and 78 ± 2.19 m in diameter. A mean of 26 ± 0.63 lateral branches are found on fully developed cotylephores. Each branch terminates in a wide apical calyx, approximately 112 ± 4.16 m in diameter, to which the egg envelope adheres. Adjacent calyces of the same cotylephore establish attachments with the envelope of a single egg. Cotylephores are composed of a surface epithelium that is continuous with the skin and a fibrous connective tissue core that contains blood vessels that ramify into an apical capillary plexus. The plexus may function in maternal-embryonic metabolic exchange. The cotylephores ofSolenostomus closely resemble the epidermal stalks (cotylephores) that are the sites of egg attachment in the skin-brooding South American catfish,Platystacus cotylephorus. Based on similarity in structure and probable function, cotylephores in the two groups of fishes are an example of evolutionary convergence.     

Capacitance,short-circuit current and osmotic water flow across different regions of the isolated toad skin

Summary The amphibian antidiuretic hormone, arginine vasotocin, stimulated osmotic water flow across isolated skin from the pelvic but not the pectoral skin of the toad, Bufo woodhouseii. Changes in the apical membrane capacitance were not observed for either region of the skin following treatment with arginine vasotocin when there was an osmotic gradient across the tissue. In the absence of an osmotic pressure gradient, the apical membrane capacitance of the pelvic skin increased from 2.8±0.5 to 3.3±0.6 F · cm^-2 after treatment with 5 · 10^-8 M arginine vasotocin. Under these conditions, apical membrane capacitance of the pectoral skin was 1.8±0.1 F · cm^-2 and did not change significantly after arginine vasotocin treatment. The amiloride-sensitive short-circuit current across the pelvic skin was stimulated by arginine vasotocin as was the density of channels in the apical membrane as determined by fluctuation analysis. Values for channel density in the pelvic skin also correlated with apical membrane capacitance and increased from 90 to 273 channels per m² of estimated membrane area following arginine vasotocin treatment. In the pectoral skin the stimulation of short-circuit current following arginine vasotocin treatment was small and an increase in channel density could not be demonstrated. The current through single Na⁺ channels in both regions of the skin did not different either before or after arginine vasotocin treatment.Abbreviations A amiloride - ADH antidiuretic hormone - AVT arginine vasotocin - C capacitance - C _a capacitance of apical membrane - f _c corner frequency - i single-channel current - osmotic water flow - IMP intramembrane particles - I _sc short-circuit current - amiloride-sensitive short-circuit current - M channel density - P _o probability of a channel being open - R channel receptor - R _a apical resistance - R _p paracellular resistance     

Etiology of infectious diseases in cultivated Chondrus crispus (Gigartinales,Rhodophyta)

The appearance of cavities and holes in fronds of commercially cultivated Chondrus crispus is described. These ultimately arise from the ravages of a green spot or green rot disease system in which several biotic agents can participate. Nematodes capable of bacterial grazing were recovered from necrotic lesions and we suggest that the nematodes can facilitate wound healing in diseased tissues. Bacteria isolated from disease lesions and from the surfaces of healthy fronds were screened for pathogenic strains. A particularly virulent one, the DOR isolate, was purified from small dark orange colored colonies grown on dilution plates. It was present in necrotic tissue and also recovered from surface scrapings of old healthy fronds, but not from their apical regions. Growth of the DOR isolate appeared to be inhibited by other bacteria colonizing the algal surface. It was shown to be a facultative pathogen, the virulence of which depended on the availability of ammonium or constituents easily metabolized to ammonium. It induced green rot disease in healthy C. crispus and was recoverable in pathogenic form from experimentally infected frond apices. A wound, disease and recovery cycle is discussed to illustrate potential interrelationships involving animal grazers, algal endophytes, Petersenia pollagaster, bacteria and nematodes.     

When is a cell not a cell? A theory relating coenocytic structure to the unusual electrophysiology of Ventricaria ventricosa (Valonia ventricosa)

Summary. Ventricaria ventricosa and its relatives have intrigued cell biologists and electrophysiologists for over a hundred years. Historically, electrophysiologists have regarded V. ventricosa as a large single plant cell with unusual characteristics including a small and positive vacuole-to-outside membrane potential difference. However, V. ventricosa has a coenocytic construction, with an alveolate cytoplasm interpenetrated by a complex vacuole containing sulphated polysaccharides. We present a theory relating the coenocytic structure to the unusual electrophysiology of V. ventricosa. The alveolate cytoplasm of V. ventricosa consists of a collective of uninucleate cytoplasmic domains interconnected by fine cytoplasmic strands containing microtubules. The cytoplasm is capable of disassociating into single cytoplasmic domains or aggregations of domains that can regenerate new coenocytes. The cytoplasmic domains are enclosed by outer (apical) and inner (basolateral) faces of a communal membrane with polarised K⁺-transporting functions, stabilised by microtubules and resembling a tissue such as a polarised epithelium. There is evidence for membrane trafficking through endocytosis and exocytosis and so plasmalemma and tonoplast do not have fixed identities. Intra- and extracellular polysaccharide mucilage has effects on electrophysiology through reducing the activity of water and through ion exchange. The vacuole-to-outside potential difference, at which the cell membrane conductance is maximal, reverses its sign from positive under hypertonic conditions to negative under hypotonic conditions. The marked mirror symmetry of the characteristics of current as a function of voltage and conductance as a function of voltage is interpreted as a feature of the communal membrane with polarised K⁺ transport. The complex inhomogeneous structure of the cytoplasm places in doubt previous measurements of cytoplasm-to-outside potential difference.Correspondence and reprints: UNESCO Centre for Membrane Science and Technology, Department of Biophysics, School of Physics, University of New South Wales, Sydney, NSW 2052, Australia.     

Freshwater bryozoans (Bryozoa) of Norway IV: Distribution and ecology of four species of Plumatella with notes on Hyalinella punctata

Bryozoans were investigated during field studies of 601 lakes and other surface water bodies throughout Norway from 1960 to 1978. The frequency of occurrence of Plumatella repens was evaluated in relation to 12 environmental variables. Statistically significant deviations from the frequencies expected on the basis of random distribution were described using the categories preference, avoidance and absence. P. repens is one of the most common bryozoan species in Norway. It is represented at 227 localities in our material and by 29 additional records. The species occurred frequently all over the country, north to 71°09N (the northernmost record on the European mainland). Maximum elevation above sea level was 1052 m (maximum for Northern Europe). P. repens preferred lakes, avoided rivers, and was absent from the smallest water bodies. The species preferred (1) low elevation (2–200 m above sea level), (2) medium water temperature, (3) rich aquatic vegetation (eutrophic conditions), (4) small wave action, (5) high content of calcium and magnesium, (6) pH 6.4–9.6, and (7) rather high water colour. Otherwise P. repens avoided (1) habitats above 500 m but occurred up to 1052 m, (2) the lowest water temperature intervals, (3) sites with poor aquatic vegetation and stony shores, (4) medium wave action, (5) sites with a low calcium and magnesium content, (6) lakes of low water colour, and (7) lakes with pH below 6.6: it was absent from lakes with pH below 5.2. For many environmental variables, the species had a wider tolerance range than reported from elsewhere. P. fungosa, P. casmiana, and P. emarginata are all rare in Norway. The total numbers of known localities, with our records in (), are 18 (11), 7 (7), and 7 (5), respectively. These sites are all from lowland areas up to 133 m above sea level. Environmental variables in the habitats are described. P. fungosa was represented by a single floatoblast in each of the four northernmost lakes where it was recorded. One of these lakes was in North Norway some 1000 km away from the nearest known sites with living colonies. The presence of large colonies of P. fungosa in some parts of southern Norway and only `single floatoblast lakes' further north is discussed in relation to the equilibrium theory of island biogeography: birds facilitate immigration by carrying floatoblasts and environmental conditions prevent their germination and the development of living colonies. All records of P. casmiana and P. emarginata were from South Norway. Results for P. fruticosa have been published previously. Notes are given on an old and now missing sample from ca. 1900, identified by Lacourt (1968) as Hyalinella punctata – the only record of this species from Norway.     

The water velocity preferences of Austrosimulium furiosum and Simulium ornatipes (Diptera: Simuliidae) larvae,and the implications for micro-habitat partitioning

The aquatic larvae of two simuliid species, Austrosimulium furiosum (Skuse) and Simulium ornatipes Skuse, which often occur together in Victorian streams, were shown in laboratory experiments to have preferences for different water velocities: larvae of A. furiosum preferred water velocities of 0.2–0.3 m s^–1, and S. ornatipes preferred water velocities of 0.9–1.3 m s ^–1 . Final instar larvae of both species selected slow water speeds of less than 0.25 m s ^–1 prior to pupation. Flow patterns around a cylinder in a laboratory stream were mapped, and the distribution of A. furiosum larvae within the wake, paired vortices and horseshoe vortex was recorded. Larvae selected areas with suitable water velocities and aligned with the flow, providing flow visualization of micro-current speed and direction. The potential for micro-habitat partitioning is discussed in relation to benthic sampling strategies.     

The nutritional status of the apical meristem of Lactuca sativa as affected by NaCl salinization: An electron-probe microanalytic study

A volume of tissue of lettuce (Lactuca sativa L.) plants extending 2 mm basipetally from the apical meristem and including leaf primordia and young expanding leaves was surveyed using electron-probe microanalysis (EPMA) on both frozen-hydrated and freeze-dried samples. This analysis was carried out either 2 or 5 d following NaCl salinization of the medium from the 10 mol · m^–-3 control level up to 80 mol · m^–-3. The objective was the investigation of possible changes in the nutritional status of the apical meristem that might account for some aspects of salt-induced growth inhibition. Sodium and chloride increased significantly in tissues basal to the apical meristem, while both phosphorus and potassium decreased in the same region. These changes were evident in specimens collected just 2 d after the commencement of salinization (20 h after completion of the salinization) and were not exacerbated by an additional 3 d of treatment; they were present in tissue as close as 100 m to the meristem and extending down to 500 m. The apical 10–50 m were relatively protected from both the increase in sodium and chloride and the decrease in phosphorus and potassium that occurred in more basal regions. Young leaves (up to 1.5 mm in length) appear to control their own mineral nutrient levels when challenged by salinization of the medium, presumably because of altered growth. A decrease in the concentration of total Ca as a result of salinization was significant in cells 500 m basal to the meristem, but was evident as a tendency in the data even within the first 50 m. Using an improved automatic method for the analysis of calcium by EPMA, it was found that total Ca was reduced by salinization, especially in basal regions (500 m below the apex) and also in young leaves (1–1.5 mm in length). We suggest that the nutrition of the shoot apical meristem may be disturbed soon after salinization and that the shoot meristem might be the source of a signal to expanding leaves, as well as exerting its own direct influence over leaf emergence.Abbreviation EPMA electron-probe microanalysis This work was supported by U.S. Department of Agriculture grant 87-CRCR-1-2462.     

Ultrastructure and function of the labial nephridia and the rectum of Orchesella cincta (L.) (Collembola)

Summary The collembolan Orchesella cincta possesses a well-developed coelomoduct kidney. The presence of podocytes in the wall of the sacculus and the fact that the epithelium of the nephridial tubule has the ultrastructural characteristics of resorbing cells, indicate that this is an ultrafiltration-reabsorption kidney.Apparently also the rectum is lined by a reabsorptive epithelium; the cells possess an extensive system of apical and basal infoldings. This view is sustained by the fact that the stereology of the apical channel system varies in animals kept under different moisture conditions. During the intermoult period, both organs are subject to strong morphological changes, which are obviously related to the feeding rhythm.The authors wish to thank Dr. T. Sminia for his stimulating interest during the investigations, Dr. J.C. Jager for statistical advice and Mr. G.W.H. van den Berg for drawing the figures     

Cellular and epithelial adjustments to altered salinity in the gill and opercular epithelium of a cichlid fish (Oreochromis mossambicus)

Morphological features of the gill and opercular epithelia of tilapia (Oreochromis mossambicus) have been compared in fish acclimated to either fresh water (FW) or hypersaline water (60 S) by scanning electron and fluorescence microscopy. In hyperosmoregulating, i.e., FW-acclimated, tilapia only those mitochondria-rich (MR) cells present on the filament epithelium of the gill were exposed to the external medium. After acclimation of fish to hypersaline water these cells become more numerous, hypertrophy extensively, and form apical crypts not only in the gill filament but also in the opercular epithelium. Regardless of salinity, MR cells were never found to be exposed to the external medium on the secondary lamellae. In addition, two types of pavement cells were identified having distinct morphologies, which were unaffected by salinity. The gill filaments and the inner operculum were generally found to be covered by pavement cells with microridges, whereas the secondary lamellae were covered exclusively by smooth pavement cells.     

Intraspecific variation in the water relations of Salix arctica,an arctic-alpine dwarf willow

Summary The seasonal and diurnal water relations were investigated within arctic and alpine populations of the dwarf willow Salix arctica. Marked differences that were habitat dependent (e.g. xeric vs. mesic) occured both within and between the populations. The environmental variables that most affected plant water balance and the bulk tissue water relations were soil water potential (_soil) and the leafto-air water vapor pressure gradient (w), however, low soil temperature (<4.0° C) also had a marked effect in the wet to mesic habitats. The effects of declining _soil and increased w were most pronounced in the plants growing in xiric habitats in both populations. Stomatal response to increased w was two-fold greater in alpine versus arctic plants and is hypothesized to have arisen in response to more frequent exposure to the higher evaporative conditions of alpine existance. Seasonal fluctuations in the osmotic potential closely followed changes in _soil, suggesting that these were active rather that passive changes. Additionally, plants from xeric habiats had a lower bulk tissue elastic modulus (more elastic tissues) in both arctic and alpine populations. The osmotic and elastic properties enhanced turgor maintenance over a broad range of leaf water potentials and during periods when w was high. Turgor maintenance also correlated to continued transpiration despite fluctuations in soil and atmospherically induced water deficits. Arctic habitats have a shorter growing season, lower soil temperatures due to the presence of permafrost, but higher soil water potentials and lower leaf-to-air vapor pressure gradients than alpine habitats. The observed variation in patterns of stomatal conductance and in values of tissue water relations characteristics between arctic and alpine populations of S. arctica is hypothesized to have arisen in response to these different environmental regimes which represent different selective regimes that occur along the arctic-alpine environmental continuum inhabited by this wide ranging species.     

Phytochrome-mediated polarotropism of Adiantum capillus-veneris L. protonemata as analyzed by microbeam irradiation with polarized light

Summary Perception of polarized light inducing phytochrome-mediated polarotropism in protonemata of the fern Adiantum capillus-veneris L. was analyzed using brief microbeam irradiation with polarized red (R) or far-red light (FR). The polarotropic response inducible by irradiation of the subapical 10–30-m part with polarized R vibrating parallel to the cell axis was nullified by subsequently giving R at the apical 0–2.5-m region. This inhibitory effect of R showed an action dichroism, that is, polarized R vibrating normal to the cell axis was effective but the parallel-vibrating R was not. On the other hand, FR irradiation of the extreme tip after irradiation of the whole cell with depolarized R effectively induced a tropic response. This FR effect also showed action dichroism, with parallel-vibrating polarized FR being more effective than FR vibrating normal to the cell axis. When the apical-dome region and the adjacent subapical 10–20-m region were sequentially irradiated with polarized R vibrating obliquely in different directions, polarotropism took place depending on the vibrating direction of the light given to the apical-dome region. Obliquely vibrating polarized FR given to the apical dome after irradiation of the whole cell with depolarized R also induced polarotropism. Thus, the difference in amount (or percent) of the far-redabsorbing form of phytochrome (Pfr) between the extreme tip and the subapical region appears to be crucial in regulating the direction of apical growth; the difference in Pfr level between the two sides of the protonemal apex may occur mainly at the apical dome. Furthermore, the transition moments of the red-absorbing form of phytochrome (Pr) and Pfr seem to be aligned parallel and normal, respectively, to the cell surface at the periphery of the apical hemisphere.Abbreviations FR far-red light - Pfr far-red-absorbing form of phytochrome - Pr red-absorbing form of phytochrome - R red light     

Abscisic acid and water transport in sunflowers

The role of abscisic acid (ABA) in the transport of water and ions from the root to the shoot of sunflower plants (Helianthus annuus) was investigated by application of ABA either to the root medium or to the apical bud. The exudation at the hypocotyl stump of decapitated seedlings was measured with and without hydrostatic pressure (0–0.3 MPa) applied to the root. All ABA concentrations tested (10^-10–10^-4 mol·l^-1) promoted exudation. Maximal amounts of exudate (200% of control) were obtained with ABA at 10^-6·mol·l^-1 and an externally applied pressure of 0.1 MPa. The effect was rapid and long-lasting, and involved promotion of ion release to the xylem (during the first hours) as well as an increase in hydraulic conductivity. Abscisic acid applied to the apical bud had effects similar to those of the rootapplied hormone. Increased rates of exudation were also obtained after osmotic stress was applied to the root; this treatment increased the endogenous level of ABA in the root as well as in the shoot. Water potentials of the hypocotyls of intact plants increased when the roots were treated with ABA at 5°C, whereas stomatal resistances were lowered. The results are consistent with the view that ABA controls the water status of the plant not only by regulating stomatal transpiration, but also by regulating the hydraulic conductivity of the root.Abbreviations and symbols ABA abscisic acid - Tv volume flow - Lp hydraulic conductivity - PEG polyethyleneglycol - water potential - osmotic potential - osmotic value - P hydrostatic pressure     

Barrier membranes at the outer surface of the brain of an elasmobranch,Raja erinacea

Summary This report gives the results of the first electron-microscopic examination of the cell layers covering the outer brain surface and the inner surface of the cartilaginous skull in the skate, Raja erinacea. The perivascular glial blood-brain barrier — a characteristic of elasmobranchs — extends to the outer surface of the brain. This outer barrier layer is surrounded, in turn, by a subarachnoid compartment (depth: 30–40 m), containing loose connective tissue and blood vessels; by an arachnoid-like epithelium (10–15 cell layers), impermeable to horseradish peroxidase; and, by perimeningeal fluid, a fluid with a slow turnover rate and a protein composition different from plasma. The inside of the skull, facing the perimeningeal fluid, is covered by a multilayered (10–15 layers) cuboidal epithelium, also impermeable to horseradish peroxidase. Closely apposed cells in the luminal layer of this epithelium have apical microvilli and numerous vesicular profiles, containing material of moderate electron density. These observations may explain, in terms of structure, the regulated protein content of perimeningeal fluid and the restricted exchange of solutes between brain and perimeningeal fluid in elasmobranchs.     

Regulation of the initial segment of the murine epididymis by dihydrotestosterone and testicular exocrine secretions studied by expression of specific proteins and gene expression

The murine caput epididymidis responded to deprivation of luminal fluid from the testis by regression of the initial segment but maintenance of the adjacent proximal and distal caput regions, as judged by immuno-histochemical staining of the glutamate transporter EAAC1 and the lipocalin MEP17 and enzymatic activity of -galactosidase (-Gal). Additional removal of circulating androgens by bilateral castration similarly led to loss of the initial segment and of the proximal caput but the distal caput was transformed into an epithelium containing more apical than principal cells staining for EAAC1; this epithelium resembled the precursor epithelium usually only seen in prepubertal juveniles. Administration of dihydrotestosterone (DHT) to the castrates maintained the proximal and distal caput epithelia and induced a proximal epithelium, which resembled the initial segment in its prominent staining for Golgi, EAAC1 and -Gal activity, although it was short and exhibited no MEP17 expression. DHT was present in the c-ros knockout caput epididymidis lacking the initial segment and in the heterozygous organ but the DHT concentration was lower in the knockout corpus. The maintenance of the full complement of epithelia in the murine caput epididymidis in the adult thus requires a combination of luminal fluid from the testis, tissue DHT and the presence of the c-ros oncogene.     

Apical membrane endocytosis via coated pits is stimulated by removal of antidiuretic hormone from isolated,perfused rabbit cortical collecting tubule

Summary Antidiuretic hormone increases the water permeability of the cortical collecting tubule and causes the appearance of intramembrane particle aggregates in the apical plasma membrane of principal cells. Particle aggregates are located in apical membrane coated pits during stimulation of collecting ducts with ADHin situ. Removal of ADH causes a rapid decline in water permeability. We evaluated apical membrane retrieval associated with removal of ADH by studying the endocytosis of horseradish peroxidase (HRP) from an isotonic solution in the lumen. HRP uptake was quantified enzymatically and its intracellular distribution examined by electron microscopy. When tubules were perfused with HRP for 20 min in the absence of ADH, HRP uptake was 0.5±0.3 pg/min/m tubule length (n=6). The uptake of HRP in tubules exposed continuously to ADH during the 20-min HRP perfusion period was 1.3±0.8 pg/min/m (n=8). HPR uptake increased markedly to 3.2±1.1 pg/min/m (n=14), when the 20-min period of perfusion with HRP began immediately after removal of ADH from the peritubular bath. Endocytosis of HRP occurred in both principal and intercalated cells via apical membrane coated pits. We suggest that the rapid decline in cortical collecting duct water permeability which occurs following removal of ADH is mediated by retrieval of water permeable membrane via coated pits.     

Inhibition of Helicobacter pylori adherence by a peptide derived from neuraminyl lactose binding adhesin

Helicobacter pylori, like many other gut colonizing bacteria, binds to sialic acid rich macromolecules present on the gastric epithelium. NLBH (neuraminyl lactose binding haemagglutinin) a 32 kDa adhesin located on the surface of H. pylori has been shown to have specific affinity towards NeuAc2,3Gal1,4Gluc(3SL). This sialic acid moiety is over-expressed in an atrophic stomach undergoing parietal cell depletion. Antibodies against a lysine rich peptide fragment of NLBH inhibit agglutination of human erythrocytes. This lysine rich sequence from NLBH was proposed to be the receptor-binding site. In order to elucidate the binding of NLBH to gastric epithelium, a peptide (D-P-K-R-T-I-Q-K-K-S) was synthesized. A series of experiments were performed involving adherence inhibition assays, 2D-NMR, molecular modelling and measurement of modulation in acid secretion. Results indicated that the peptide fragment could be involved in receptor recognition, which is important for the binding of H. pylori to gastric epithelium. The binding is possibly through hydrogen bonding. Two lysines and a threonine residue seem to be within the hydrogen bonding distance of NeuAc2,3Gal1,4Gluc. Further, in vitro assays were performed to evaluate the role of the peptide on acid secretion by parietal cells isolated from human fundal biopsies. Interestingly, the peptide increases acid secretion only in H. pylori negative and in treated patients but not in H. pylori positive patients. This highlights the role of NLBH in acid secretion and could be of some consequence in the prognosis of the disease.     

Maternal-embryonic relationships in the goodeid teleost,Xenoophorus captivus

Summary The trophotaeniae and abdominal epidermis of Xenoophorus captivus embryos were studied by light, scanning and transmission electron microscopy, freeze-fracture replication, and histochemical techniques for unspecific phosphatases. The trophotaenial epithelium is continuous with both the intestinal mucosa and the epidermis, and contains structural elements similar to both. The predominant component is a simple brush-border epithelium consisting of cuboid cells showing signs of endocytotic activity at their apical surfaces. These are the absorptive elements of the trophotaeniae, and phosphatase ultracytochemistry demonstrates the presence of alkaline phosphatase on the external leaflet of their exposed plasma membranes. Enormously dilated intercellular spaces and large gaps occur in this epithelial covering.Beneath this absorptive epithelium lies an incomplete layer of dense squamous cells that appear to be derived from the stratified epithelium covering trophotaenial areas free of brush border epithelium and the abdominal wall. The exposed cell surfaces of this component are modified to form an elaborate pattern of microplicae which can be seen by scanning EM where gaps appear in the overlying absorptive epithelium. The stratified epithelium of the abdominal wall is underlain with collagen fibrils and an intricate network of capillaries, and is considered to be a site of cutaneous respiration. This cutaneous gas-exchange pathway averages 2–4 m in thickness. Chloride cells are constituents of the stratified epithelium of the trophotaenial base and abdominal wall.The involvement of the endodermal component of the trophotaenial epithelium in the transfer of nutrients and possibly antibodies, and the role of the abdominal epidermis and ectodermal trophotaenial epithelium in gas exchange and osmoregulation, are discussed.