Fine structure of clear cells in frog epidermis

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.

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.

Flask cells and flask-shaped glandular cells of amphibian skin specifically produce fucose-rich glycoproteins

A battery of horseradish peroxidase-conjugated lectins has been employed as a cytochemical tool for the labelling of specific cell types in amphibian epidermis. Among the lectins used, only Ulex europaeus I (UEA I) showed specific reaction with the cytoplasm of flask cells. In addition, UEA I stained flask-shaped secretory cells in dermal glands and a reaction on glandular ductal cells was also observed. At the electron microscopic level, lectin binding was found in granules distributed among mitochondria in the cytoplasm of flask cells and in larger mucous granules of flask-shaped glandular cells, which were released into the lumen. UEA I also stained the extracellular space above flask cells. The labelling was due mainly to a glycoprotein of mol. wt. approx. 27 kDa. Structural and cytochemical similarities between flask cells and flask-shaped cells of dermal glands could be a consequence of a common secretory role of both cell types.

Histological changes in the skin of Rana pipiens produced by metabolic alkalosis

The frog skin has been shown to excrete various electrolytes, the rates can be altered by varying metabolic conditions. The present study was performed to determine if metabolic alkalosis results in histological changes in the skin that are characteristic of this state. Rana pipiens were loaded with NaHCO3 and skin biopsies obtained (I). These biopsies were compared with biopsies from either control, unloaded frogs (II), or from NaCl loaded (III) frogs. In blind studies of microscopic sections, 13 of 15 biopsies of a mixture of I and II were correctly diagnosed, and similarly, 18 of 20 of I and III were correctly diagnosed (P = 0.0037, and 0.0002, respectively). The changes due to NaHCO3 treatment included; (1) an abundance of large euchromatin cells on or near the surface; (2) changes in the basal cell layer with elongation and rotation of the nuclei; (3) lighter cells in the spinosal layer; and, (4) sometimes the skin became thicker. We conclude that metabolic alkalosis results in characteristic histological changes in the skin, and that this is probably related to the ability of the skin to excrete bicarbonate.

Polarization of plasma membrane glycoconjugates in amphibian epidermis during metamorphosis

Wheat germ agglutinin (WGA) binding sites have been examined in tadpole epidermal cells at the level of both light and electron microscopy using the WGA-ovomucoid-gold technique. In premetamorphic tadpoles the reaction was observed on the plasma membranes of epithelial cells showing a gradient from inner to outer membranes. These glycoconjugates were polarized during development, and at the end of metamorphic climax they were only located in plasma membranes of stratum corneum. The existence of an apical cell surface coat is needed to facilitate the absorption of water through the adult epidermis. The possible implications of this polarization process are discussed.

Morphology of ventral epidermis of Rana catesbeiana during metamorphosis

A detailed morphological examination of the bullfrog tadpole ventral epidermis and changes in structure that occur during metamorphosis has not been done. Knowledge of this is crucial to interpretation of physiological studies such as those dealing with development of transepithelial Na+ transport. Examination of tadpole epidermis with light microscopy reveals the presence of three different cell types: apical, basal, and skein. This epidermal morphology is constant until Taylor and Kollros (Anat. Rec. 94:7-23, 1946) stage 19 when degeneration of apical cells is noted. Stages 20 and 21 are characterized by rapid proliferation of basal cells and development of a true stratum germinativum together with the disappearance of other tadpole cell types. By stage 22, epidermal morphology is similar to that of the adult frog. Studies with the electron microscope reveal that as the proliferation proceeds during metamorphosis, the skein cells, at stage 20, differentiate to form the apical border of the skin. The development of the adult frog cell phenotype appears to mimic the cellular differentiation that occurs in the adult epidermis with the cells first developing into progranular cells in the intermediate stratum of the skin and then progressing to granular cells in the outermost living cell layer. The granular cells then undergo cornification to form the stratum corneum. Mitochondria rich cells are not seen in the developing epidermis until stage 21. These observations, when considered with previous results from Na+ transport studies (Hillyard et al.: Biochim. Biophys. Acta 692:455-461, 1982), suggest that both the physiological differentiation and morphological differentiation are simultaneous events.

Lectin binding patterns in amphibian epidermis

A battery of 6 different horseradish peroxidase conjugated lectins has been employed for structural localization of glycoconjugates in amphibian epidermis. Lens culinaris (LCA) lectin stained the basal membrane and gave no significant reaction on the epidermal layers. Canavlia ensiformis (Con A) and Griffonia simplicifolia II (GS II) lectins bound the keratinocyte cytoplasm and the basal membrane as well. Ulex europaeus I (UEA I) lectin had only reactivity with flask cells. Griffonia simplifolia I (GS I) and Glycine max (SBA) lectins preferentially bound the cell membranes of keratinocytes, being the intensity of the staining gradually increasing from the stratum spinosum to the stratum granulosum. These results show that UEA I, GS I, and SBA are good markers to distinguish different cell types and the degree of keratinocytes differentiation.

Morphology of the exocrine glands of the frog skin

Frog skin contains three distinct types of exocrine glands: granular (poison), mucous, and seromucous. The granular gland forms a syncytial secretory compartment within the acinus, which is surrounded by smooth muscle cells. The mucous and seromucous glands are easily identifiable as distinct glands. The serous and mucous secretory cells are arranged in a semilunar configuration opposite the ductal end and are filled with granules. Within the acinus, located at the ductal pole of the gland, are distinct groups of cells with few or no granules in the cytoplasm. In both the mucous and seromucous gland there is a cell type with abundant mitochondria; the one in the mucous gland is located in the region adjacent to the secretory cells. The duct of these glands is two-layered, with the individual cells appearing morphologically similar to the layers of the skin epithelium as the duct traverses the skin. The duct appears to be patent throughout its length. The morphological heterogeneity and distinct distribution of the cell types within the gland acinus may be indicative of a functional heterogeneity that allows the production of distinctly different types of secretion from the same gland type, depending on the type of stimulus.

Modification of mitochondria-rich cells in different ionic conditions: changes in cell morphology and cell number in the skin of Xenopus laevis

Xenopus laevis were kept in salt water (1.25% NaCl), distilled water, or tapwater for a month. Compared to the animals kept in tap water, the number of mitochondria-rich (MR) cells in the NaCl-adapted animals was significantly reduced, while it was increased in those maintained in distilled water. In addition, the MR-cells of NaCl-adapted animals lost their slender flask shape and developed large deposits of glycogen. The alteration of this cell type in conditions of high or low salinity may reflect a role of MR-cells in adaptation to different ionic environments.

Rod-shaped particles in the plasma membrane of the mitochondria-rich cell of amphibian epidermis

A freeze-fracture study has revealed rod-shaped intramembranous particles on the plasma membrane P-face (cytoplasmic leaflet) of the mitochondria-rich cell (or flask cell) of Xenopus laevis and Rana ridibunda epidermis. Such particles have previously been found in all other mitochondria rich cells examined by this technique, namely, the MR-cell of toad bladder epithelium, the dark cell of rat kidney collecting tubule, and the flask cell of Xenopus kidney collecting tubule. These particles are assumed, therefore, to be closely connected with the function of this cell type.

Utrastructure of the cement gland of Xenopus laevis

To establish a morphological baseline for experimental studies of differentiation using the cement gland as a model, the following observations are added to those on record. The elongated cells of Xenopus laevis cement glands have an internal organization displaying five distinct zones differing in structure and specialized function. The apical zone contains packed secretion vesicles apparently belonging to two different types. The transit zone appears to be devoid of major biosynthetic activity and contains secretion vesicles migrating toward the surface. The zone of biosynthesis is typically organized in concentric regions. The very elongated nucleus lies in the next zone. Finally, the storage zone is characterized by lipid droplets and yolk platelets. Only quantitative differences are observed between cells of young and mature cement glands. Though all cells have the same general organization they may probably be divided into two subtypes according to the structure of their cytoplasm. The epithelial cells surrounding the gland differ according to their position along lateral or basal borders.

Aldosterone-induced moulting in amphibian skin and its effect on electrical capacitance

The resistance and capacitance of the isolated amphibian skin have been determined from measurements of the response of the voltage across the skin to small steps to current. Previous work indicates that the electrical impedance of frog skin, when the skin is bathed with Ringer's solution on both sides, is largely determined by the properties of the functional outward-facing membrane of the skin, the outer membrane of the stratum granulosum (P.G. Smith, 1971, Acta Physiol. Scand. 81:355). This membrane can be represented by a resistance and capacitance in parallel. Aldosterone, which induces conversion of the s. granulosum into a cornified cell layer and transformation of the cell layer below into a new s. granulosum, also causes a transient rise in resistance and a short-lived decrease in capacitance to about one-half its initial value. It is suggested that these electrical changes are caused by the transitory presence of two functional outward-facing membranes in series. The method of determining resistance and capacitance from the voltage response is discussed in the Appendix.