Enzyme cytochemical and immunocytochemical studies of flask cells in the amphibian epidermis

Histological and immunohistochemical characterization of the integument and parotoids glands Rhinella bergi (Anura: Bufsonidae): Development and differentiation

A detailed description of the tegument and parotoid glands of pre-metamorphic, post-metamorphic, juvenile and adult individuals of Rhinella bergi is presented to provide an exhaustive analysis of the integumentary characteristics of this species. Fragments of the tegument were fixed in Bouin solution and preserved in buffered Formol 10%. Subsequently, scanning electron microscopy (SEM) was performed to characterize the macroscopic structure of these regions. Microscopic observations were made from histological sections stained with Hematoxylin and Eosin, Alcian Blue (pH 2,5), PAS-H, Coomassie Blue, Oil Red, and Bielschowsky Impregnation.. There were three types of protuberance: warts, tubers, and thorns. These structures became evident from post-metamorphic stages. The ventral surface shows elevations similar to flat warts; however, tubers and spines are absent. Histologically, each structure consists of a spongy dermis of lax connective tissue and dense and compact dermis, associated with granular glands and a keratinized epidermis. The latter, in the dorsal region, forms projections called thorns. The granular glands accumulate, and their alveoli increase in size progressively. This work provides a morphological and histological description of the integument and the parotoid glands during the larval and post-metamorphic stage of the genus Rhinella, with aspects described for the first time in the genus.

Immunohistological classification of ionocytes in the external gills of larval Japanese black salamander, Hynobius nigrescens Stejneger

In this cytological and immunohistological study, we clarified the localization of the membrane transporters Na(+) , K(+) -ATPase (NKA), vacuolar-type H(+) -ATPase (VHA), and epithelial sodium channel (ENaC) and distinguished ionocyte subtypes in the gill of the Japanese salamander (Hynobius nigrescens). In larvae (IY stages 43-65), NKA immunoreactivity was observed on the basolateral plasma membrane in more than 60% cells and less than 20% cells in the primary filaments and secondary lamellae of the external gills, respectively. VHA immunoreactivity was observed on the apical membrane of some epithelial cells in the secondary lamellae of the external gills. High ENaCα immunoreactivity was widely observed on the apical cell membrane of a population of squamous cells, presumably pavement cells (PVCs), and mitochondria-rich cells (MRCs), in the primary filaments and secondary lamellae of the external gills. Using double immunofluorescence microscopy, epithelial cell types involved in ionic regulation were characterized and divided into three ionocyte types: NKA-, NKA- and ENaC-, and VHA-positive cells. VHA-immunoreactive cells as well as NKA-positive cells were observed during IY stages 43-65 of the salamander larvae. During late stages of metamorphosis, NKA, VHA, and ENaCα immunoreactivities in the external gills decreased and finally disappeared during the completion of metamorphosis (IY stage 68). PVCs and MRCs in the external gills are probably involved in acid-base balance regulation and osmoregulation in urodele amphibian larvae. The results are discussed in relation to the ionocytes previously reported in fish gills and the frog skin epithelium.

Morphofunctional evidence of changes in principal and mitochondria-rich cells in the epidermis of the frog Rana kl. esculenta living in a polluted habitat

The epidermis of vertebrates is the body's principal barrier against environment and its possible contaminants. The presence of keratins, as well as specific detoxifying molecules or enzyme activities, in the various epidermis layers is believed to be involved in providing protection from harmful environmental influences. Anuran integument is poorly hornified and thus permeable to some endogenous and exogenous compounds and thus serves as a good bioindicator of overall environmental conditions. In the present investigation, we studied the epidermis of Rana kl. esculenta adult specimens collected at two different rice fields, relatively unpolluted and heavily polluted, respectively. Environmental pollution was assayed by chemical analysis performed on both sediments and animals. We evaluated the structural aspects of the epidermis at both light and electron microscopy levels and the pattern of keratinization by immunohistochemistry. Furthermore, we studied the activities of some enzymes (acid and alkaline phosphatase, nitric oxide synthase-related nicotinamide adenine dinucleotide phosphate dehydrogenase, glucose-6-phosphate dehydrogenase, catalase, nonspecific esterases, and succinic dehydrogenase) involved mainly in membrane transport, xenobiotics, and oxidative metabolism. Compared with controls, in polluted animals we found the following results: (1) an increase in pollutant levels (i.e., cadmium, mercury, and lead); (2) less keratinized superficial cells in the epidermis; and (3) changes in most enzyme activities in keratinocytes and mitochondria-rich cells (particularly glucose-6-phosphate dehydrogenase and esterases, both important to counteract oxidative and toxic stress). Taken as a whole, the present data indicate the morphofunctional plasticity of the frog epidermis in response to environmental contamination.

Enzymatic changes in mitochondria-rich cells of Xenopus laevis skin epithelium are induced by ionic acclimation

Morphological, biochemical and histochemical components of mitochondria-rich (MR) cells of skin epithelium of Xenopus laevis (Daudin) were investigated after acclimation in distilled water (DW) and mild solutions (50 mmol/l) of either NaCl or KCl for over 10 days. The animals readily acclimated to NaCl, but approximately 50% of the animals died in the KCl solution. Electrophysiological measurements confirmed the poor transport properties of skin in all conditions. Silver staining and exposure to methylene blue (MB) have shown that two types of MR cells can be distinguished, especially after KCl acclimation. Immunohistochemistry with the use of anti-band 3 polyclonal and anti H+-ATPase monoclonal antibodies demonstrated that band 3 and H+-ATPase enzymes were localized in MR cells in all conditions. H+-ATPase was greatly reduced during NaCl acclimation as verified with SDS gel electrophoresis. Intensity of the immunohistochemical staining differed between the various conditions of acclimation. Histochemical localization of carbonic anhydrase and alkaline phosphatase activities was more intense during NaCl acclimation. Morphological changes were also observed between the various acclimation conditions. The present findings substantiate the existence of at least two forms of MR cells in Xenopus skin epithelium but their functional significance remains to be established.

Mitochondria-rich cells in anuran amphibia: chloride conductance and regional distribution over the body surface

The distribution and density (D(mrc)) of mitochondria-rich cells (MR cells) in skin epithelium, were determined over the whole body surface in nine species of anuran Amphibia that live in a variety of habitats. It was found that the more terrestrial species (beginning with Hyla arborea) have a higher density of MR cells in their pelvic region. In the skin of aquatic (Xenopus laevis) or fossorial (Pelobates syriacus) species, D(mrc) is evenly distributed over the whole body surface. In dorsal skin pieces of H. arborea that lack detectable MR cells, transepithelial voltage activation did not induce Cl(-) conductance as it did in ventral pieces. Skins from Bufo viridis and X. laevis, both have MR cells in their skin, differ markedly in their biophysical properties: a Cl(-) specific current conductance is predominant in the skin epithelium of B. viridis, and is absent in X. laevis. In the latter, anionic conductance is due to glandular secretion. The biophysical properties cannot therefore be related solely to the presence or density of MR cells. Mitochondria-rich cells are sites of Cl(-) conductance across the skin of those amphibians that show this property, but must have different function(s) in other species. It is suggested that the specific zonal distribution of MR cells in the species that were examined in this study could be due to ion exchange activity and water conservation in more terrestrial environments.

Lectin binding patterns in amphibian skin epithelium

Seven lectins (PNA, DBA, WGA, UEA-I, RCA, SBA, Con A) were used to localize glycoconjugates in the skin of 10 species of Amphibia, 7 anurans (Bufo marinus, Bufo bufo, Rana ridibunda, Rana pipiens, Hyla arborea, Pelobates syriacus and Xenopus laevis) and 3 urodeles (Salamandra salamandra, Triturus vulgaris and Ambystoma mexicanum). It was found that every lectin has a specific binding pattern in the skin of each species. No common pattern could be established, either among frogs or toads, nor for a particular lectin. Each lectin bound specifically and selectively to a particular epithelial component, which differed from one species to the other. A number of lectins showed selective binding to mitochondria-rich cells, but, again, a pattern in positivity could not be found. It is concluded that lectin histochemistry does correlate with cellular function. Our data can be applied in studies of epithelium and skin development, and of changes that occur during adaptation to the environment by amphibian species.

The structure of the skin of the tree frog (Hyla arborea arborea L.)

The aim of the study was to investigate the structure of the skin of the adult tree frog Hyla arborea arborea L. by scanning electron microscopy (SEM) and light microscopy (LM). SEM observation shows that the skin from the dorsal part of body is smooth whereas the ventral part has regular ridges and grooves. The superficial layer of the skin consists of irregular shaped epidermal cells covered with microridges differing on the dorsal and ventral skin. Two types of gland outlets, funnel-type and collar-type, are seen on the surface of the epithelium. The dorsal and ventral skin observed in LM contained three kinds of glands: mucous glands, and two different types of serous glands, type I and II. The mucous glands are small and located in the upper layer of the stratum spongiosum of the connective tissue. The serous glands are large. Type I glands with small secretory granules (1-3 microns) appear sporadically in both the dorsal and ventral skin. Type II glands with large secretory granules (5-15 microns) are very numerous, particularly in the dorsal skin. Many capillaries invaginate to the epidermis of the ventral skin facilitating absorption of water in these sites. The lipid glands occurring in the skin of phyllomedusine frogs are not observed in the skin of the tree frog.

Cytochemical and immunocytochemical investigations on epidermal mitochondria-rich cells in Salamandra salamandra salamandra (L.) larvae

In the present study we set out to investigate the expression of E-cadherin, N-cadherin, beta 1-integrin, fibronectin and vitronectin in the mitochondria-rich cells (MRC) of the skin of Salamandra salamandra salamandra. Moreover MRC were stained with five lectins (Triticum vulgaris; Dolichos biflorus; Glycine max; Arachis hypogaea and Canavalia ensiformis). Larval MRC expressed both adhesion molecules and extracellular matrix glycoproteins and bound all lectins tested. Juvenile MRC did not react with the antisera utilized, but they stained with the lectins. Both the lectins and the regulatory molecules proved to be good cytochemical markers for distinguishing morphologically differentiated MRC during the larval life of Salamandra salamandra salamandra. The adhesion molecules and matrix glycoproteins are of great utility for maintaining the correct tissue architecture. In Salamandra salamandra salamandra larvae these molecules may be crucial for stability and for the correct localization and fate of all skin elements, including specialized cells such as larval MRC.

Ultrastructure of ventral epidermis in the terrestrial and aquatic phases of the newt Triturus vittatus (Jenyns)

The ultrastructure of the ventral epidermis is described in the aquatic and terrestrial phases of the newt Triturus vittatus (Jenyns). In both phases, the stratum corneum is characterized by a large number of keratinocytes and bundles of tonofilaments. Mitochondria-rich flask cells were found in both phases. The main difference was found in the abundant tuberculi on the surface, and in the number of stratum corneum replacement layers found in the terrestrial phase. The epidermis of the aquatic phase did not show any resemblance to the aquatic larval stage, thus no Leydig cells could be found.

Selenium-induced autometallographic demonstration of endogenous zinc in organs of the rainbow trout, Salmo gairdneri

Autometallographic (AMG) silver enhancement of endogenous zinc was studied in seven organs of the rainbow trout Salmo gairdneri. Groups of trout were injected intraperitoneally with sodium selenite in doses ranging from 0.08 to 25 ppm, administered 1 h before being killed. The concentration of selenium obtained by each organ was determined by gamma-spectrometry, and compared with the autometallographic deposition of silver grains. The relative accumulation of selenium in the organs was: liver greater than spleen greater than kidney greater than intestine greater than gills greater than brain greater than muscle. In the fish labelled with 10 and 25 ppm Se, AMG-deposits were found (1) within lysosomes of liver cells, (2) within the granules and on the nuclear membrane of melanophores in the spleen, (3) on the microvilli and in the apical cytoplasm of renal proximal tubular cells, (4) within the granules and along the plasma membrane of intestinal eosinophilic granule cells, and in the apical portion of the intestinal epithelium, and (5) in the gills, within granule cells and on the surface of the ionocytes. In the trouts injected with 5 ppm Se, silver grains were still observed in the liver, the intestine, and the gills, whereas, no such grains were found in preparations from fish having received 1 ppm Se. The use of selenium for the histochemical demonstration of endogenous zinc versus exogenous metals is discussed. Also, consideration is given to the question of which part of the total tissue zinc that is histochemically reactive.

Sulfate transport in toad skin: evidence for mitochondria-rich cell pathways in common with halide ions

1. In short-circuited toad skin preparations exposed bilaterally to NaCl-Ringer's containing 1 mM SO2(-4), influx of sulfate was larger than efflux showing that the skin is capable of transporting sulfate actively in an inward direction. 2. This active transport was not abolished by substituting apical Na+ for K+. 3. Following voltage activation of the passive Cl- permeability of the mitochondria-rich (m.r.) cells sulfate flux-ratio increased to a value predicted from the Ussing flux-ratio equation for a monovalent anion. 4. In such skins, which were shown to exhibit vanishingly small leakage conductances, the variation of the rate coefficient for sulfate influx (y) was positively correlated with the rate coefficient for Cl- influx (x), y = 0.035 x - 0.0077 cm/sec (r = 0.9935, n = 15). 5. Addition of the phosphodiesterase inhibitor, 3-isobutyl-1-methyl-xanthine to the serosal bath of short-circuited preparations resulted in a significant stimulation of the passive Cl- and SO2(-4) permeabilities. 6. It is suggested that SO2(-4) and Cl- ions are transported along the same pathway of the m.r. cells. Depending on the transport mode of the apical Cl- transport system, electro-diffusion, active transport (sulfate:bicarbonate exchange) and self-exchange diffusion take place. Irrespective of the mechanism of transport, sulfate is probably transported as a monovalent anion species.

Carbonic anhydrase cytochemistry in mitochondria-rich cells of salamander larvae gill epithelium as related to age and H+ and Na+ concentrations

Carbonic anhydrase (CAH) was localized in the mitochondria-rich cells (MRC) of 1-week-old salamander larvae gill epithelium, in both MRC and pavement cells of 6-week-old larvae, and in regenerated stems of previously amputated gills. CAH activity of the MRC was measured quantitatively using a microscope densitometric technique. Changes in CAH activity per cell and changes in the numbers of CAH-positive MRC were followed under different H+ and Na+ concentrations at the two age groups. CAH activity per cell increased with age, whereas the numbers of CAH-positive MRC dropped. CAH activity per cell in the 1-week-old age group reached maximal values at pH 7.4 and stayed relatively high in the more alkaline media. Moderate increases of Na+ concentrations had small but significant effects on increasing CAH activity of gill MRC. When taking into consideration not only the changes in cellular activity but also the changes in the number of CAH-positive cells under the different acclimation media, an activity index (ICAH) was calculated. Thus, the ICAH in the 1-week-old was found to be dependent on the decline of ambient H+ concentrations (expressed as increasing pH), reaching maximal effect at pH 8.0. On the other hand, raising the Na+ concentrations of the acclimation media to 110 and 220 mOsm/liter caused a maximal inhibition of tissue CAH activity as expressed by ICAH. In conclusion, it is suggested that salamander larvae gill MRC take part in the adaptation of the larvae to changing H+ concentrations of their milieu rather than in their adaptation to changes in its osmolality.