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PubMed1982

Further freeze-fracture studies on the uterine epithelium of Salamandra salamandra (L.) (Amphibia, Urodela) using the antibiotic filipin.

The apical portion of the uterine lining of the ovoviviparous fire salamander, Salamandra salamandra, was studied by the freeze-fracture technique in conjunction with the polyene antibiotic filipin. Filipin-sterol complexes were found in the luminal plasmalemma and in the membranes limiting the mucous secretory granules typical of this epithelium. In all females, but particularly in non-pregnant females, more or less discrete clusters of filipin-sterol complexes were occasionally found overlying heavily affected secretory granules. The findings are discussed with regard to comparable results (Orci et al. 1980) based on the examination of collapsed and stretched urinary bladders of toads.

Animals↗
PubMed1977

Structural correlates of function in the "opercularis" muscle of amphibians.

This study characterizes the fine structure of the "opercularis" muscles of selected frogs and salamanders (Genera: Hyla; Desmognathus; Ambystoma). The "opercularis" muscle originates on the shoulder girdle and inserts on the opercular plate in the fenestra ovalis of the otic capsule. Each of the three genera used exhibits one of the major gross dispositions of this muscle found in amphibians. In each case the "opercularis" muscle contains large numbers of tonic fibers: 80% in Hyla; 90% in Desmognathus; 45% in Ambystoma. These fibers correspond to the class-5 tonic fibers of Smith and Ovalle (1973). The remained of the fibers in the "opercularis" correspond to those in the class-3 "phasic" of Smith and Ovalle. The muscle from which the "opercularis" is derived (levator scapulae in Hyla, cucullaris in Desmognathus) is comprised of fibers which correspond to the class-2 phasic fibers of Smith and Ovalle. The fiber composition of the "opercularis" indicates that it is constructed to sustain contraction over long periods of time. This composition is supportive of the functional role in audition proposed for the muscle by Lombard and Straughan (1974). Evidence is presented that indicates that fiber size may be body size dependent and thus is an inappropriate criterion of fiber type identification.

Amphibians↗
PubMed1976

Temperature dependent changes in the thyroid gland of Mertensiella caucasica (Urodela, Amphibia).

The influence of temperature on the thyroid gland of the Caucasian salamander, Mertensiella caucasica has been studied (1) with the light- and electron microscopes, (2) with enzyme histochemical and quantitative methods. Animals which had been kept for years at 16 degrees C were exposed for 48 hrs to 4 degrees C or 27 degrees C. At 4 degrees C the follicular epithelium consisted of cuboidal cells with well-developed rough ER, occasional distended cisternae of the rough endoplasmic reticulum (ER) filling most of the cytoplasm, a relatively small Golgi apparatus and numerous round or oval shaped lysosomes. In animals kept at 27 degrees C the follicular wall was composed of markedly taller epithelial cells, the apices of which bulged into the follicular lumen. Compared to the animals at 4 degrees C, there appeared to be a decrease in the rough ER. The Golgi apparatus did not exhibit clear differences. The lysosomes increased in number and showed various shapes among which elongated ones with pointed ends were particularly striking. In the apical cytoplasm colloid droplets appeared indicating hormone release. The apical microvilli increased in number. The measurements of total T4 have shown that the hormone level in animals kept at 27 degrees C was about twice as high as in animals kept at 4 degrees C.

Animals↗
PubMed1991

Calcium handling in myocardium from amphibian, avian, and mammalian species: the search for two components.

Steps involved in excitation-contraction coupling in mammalian myocardium have been derived using a relatively limited number of animal species. However, the use of animal models for investigations into excitation-contraction coupling in normal and disease states has encompassed a wide range of animal species. We addressed the question as to whether excitation-contraction coupling as currently understood applies to intracellular calcium handling in myocardium from multiple mammalian species, amphibian, and avian myocardium. The bioluminescent calcium indicator aequorin was used to record intracellular calcium transients in both ventricular and atrial tissue. We report that in all mammalian and avian species studied the calcium transient recorded in both ventricular and atrial myocardium is monophasic and reflects calcium release and re-uptake by the sarcoplasmic reticulum. In contrast, the Ca2+ transient recorded from salamander myocardium is prolonged relative to mammalian and avian myocardium, and appears to reflect in part trans-sarcolemmal calcium entry. Only in diseased myocardium derived from human and swine myocardium was a second component detected in the calcium transient. These data indicate that sarcoplasmic reticulum calcium handling is pivotal in excitation-contraction coupling for multiple species with differing physiologies. Also, in disease states, intracellular calcium handling is often affected with resultant alterations in the time-course and/or configuration of the calcium transient.

Aequorin↗
PubMed1995

Activin A and transforming growth factor-beta stimulate heart formation in axolotls but not rescue cardiac lethal mutants.

In the Mexican axolotl (salamander), Ambystoma mexicanum, a recessive cardiac lethal mutation causes an incomplete differentiation of the myocardium. Mutant hearts lack organized sarcomeric myofibrils and do not contract throughout their lengths. We have previously shown that RNA purified from normal anterior endoderm or from juvenile heart tissue is able to rescue mutant embryonic hearts in an in vitro organ culture system. Under these conditions as many as 55% of formerly quiescent mutant hearts initiate regular contractions within 48 hours. After earlier reports that transforming growth factor-beta 1 and, to a lesser extent, platelet-derived growth factor-BB could substitute for anterior endoderm as a promoter of cardiac mesodermal differentiation in normal axolotl embryos, we decided to examine the effect of growth factors in the cardiac mutant axolotl system. In one type of experiment, stage 35 mutant hearts were incubated in activin A, transforming growth factors-beta 1 or beta 2, platelet-derived growth factor, or epidermal growth factor, but no rescue of mutant hearts was achieved. Considering the possibility that growth factors would only be effective at earlier stages of development, we tested transforming growth factors-beta 1 and beta 5, and activin A on normal and mutant precardiac mesoderm explanted in the absence of endoderm at neurula stage 14. We found that, although these growth factors stimulated heart tube formation in both normal and mutant mesoderm explants, only normal explants contained contractile myocardial tissue. We hypothesize that transforming growth factor-beta superfamily peptides initiate a cascade of responses in mesoderm that result in both changes in cell shape (the basis for heart morphogenesis) and terminal myocardial cytodifferentiation. The cardiac lethal mutation appears to be deficient only in the latter process.

Activins↗
PubMed1975

Chromomere number and its genetic significance in lampbrush chromosomes.

The chromosomes of three species of salamander belonging to the genus Plethodon have been studied with regard to the absolute length of the haploid set of lampbrush chromosomes and the number and distribution of chromomeres per laploid set of lampbrush chromosomes. Each aspect has been considered in relation to the substantial difference in genome size between P. cinereus (C = 20 pg), P. vehiculum (C = 36.8 pg) and P. dunni (C = 38.8 pg). --Karyotype analyses carried out on unfixed preparations of lampbrush chromosomes showed that the absolute length of a haploid complement of lampbrush chromosomes from medium-sized yolky oocytes is much greater for P. vehiculum and P. dunni than for P. cinereus. Nonetheless, the relative dimensions of chromosomes are nearly identical in all three species. --Chromomers were counted along the whole length of the 14th (shortest) bivalent, and the total number of chromomeres in the haploid set of lampbrush chromosomes was determined by extrapolation on the basis of the known relative length of the 14th bivalent in the respective species. Chromomeres were also counted in measured segments of undamaged lampbrush preprations in which all chromosomes could be clearly identified. The average distance between chromomeres (chromomere distribution) was determined and the total chromomere number was estimated on the basis of measured total length of lampbrush chromosomes in a preparation. Chromomere distribution is the same for lampbrush chromosomes from all 3 species, and since P. vehiculum and P. dunni have longer chromosomes than P. cinereus, it is clear that the former 2 species have many more chromomeres (60-70%) per haploid set of lampbrush chromosomes. The term chromomere was used here in the descriptive sense to define a discrete granule of deoxyribonucleoprotein on the axis of a lampbrush chromosome.--These findings are discussed in relation to what is known of the molecular organization of eukaryotic genomes, and in relation to ideas on gene action and transcription in lampbrush chromosomes.

Animals↗
PubMed1990

Multitubular bodies in intestinal cells of Amphiuma means/tridactylum (Urodela): ultrastructural characterization.

The jejunal absorptive cells of the salamander Amphiuma, when examined using transmission electron microscopy, were found to possess a unique type of intracellular vacuole containing membranous tubules. These vacuoles, tentatively named multitubular bodies, were located in the cytoplasm between the nucleus and the brush-border membrane, and were seen with greatest frequency in the summer and fall. The vacuoles containing multitubular bodies had an average diameter of 0.6 microns, and the membranous tubules within had an average diameter of 30 nm. The tubules differed morphologically from the vesicles in the multivesicular bodies, and from the primary lysosomes in the polylysosomal vacuoles. The tubules did not exhibit acid phosphatase activity, and were of similar diameter and membrane thickness as the Golgi saccules. In contrast to the multivesicular bodies, the multitubular bodies did not take up exogenous horseradish peroxidase. Early forms of autophagosomes resembling these vacuoles were often seen in the para-Golgi region of the cell. The multitubular bodies may represent a distinct type of autophagosome. Although the exact origin of the tubules as well as their role in cellular activity is unclear, their seasonal appearance within the multitubular bodies of the absorptive cells suggests a unique means of selective down-regulation of Golgi-like organelles.

Acid Phosphatase↗
PubMed1983

The dark brown integumentary pigment of a barnacle (Balanus eburneus). A comparative study.

A histochemical analysis involving tinctorial and solubility tests was pursued in conjunction with electron microscopy for the purpose of identifying the dark brown epidermal pigment of a barnacle (Balanus eburneus) as melanin and/or ommochrome. Histochemically, comparisons were made with other brown pigments located in the subcarapal epidermis of another crustacean, the fiddler crab (Uca pugilator), the dorsal skin of the red-backed salamander (Plethodon cinereus), the liver and testis of a slider turtle (Chrysemys sp.) and the substantia nigra of human brain. The solubility properties of the pigment of the two crustacean invertebrates were in general similar to one another and markedly different from the pigment of the three vertebrates. Insolubility in appropriate solvents classified the vertebrate pigment as melanin. The invertebrate pigment, however, which was soluble in the ommochrome solvents, concentrated sulfuric and formic acids and 2-chloroethanol, remained insoluble in the ommochrome solvents, dilute aqueous and methanolic hydrochloric acid and dilute sulfuric acid. On the basis of these solubilities, an unequivocal classification of the invertebrate pigment as either melanin or ommochrome did not appear possible. The tinctorial and electron microscopic properties of the barnacle pigment were also equally ambiguous in regard to its specific classification.

Animals↗
PubMed1995

Molecular characterization of a centromeric satellite DNA in the hemiclonal hybrid frog Rana esculenta and its parental species.

Hybrid water frogs Rana esculenta reproduce by hybridogenesis: one parental genome (of Rana lessonae) is excluded in the germ line, the other (of Rana ridibunda) is clonally transmitted to haploid gametes. The two parental species differ in that the amount of centromeric heterochromatin revealed by differential staining is much higher in Rana ridibunda. An abundant, tandemly arrayed, centromeric satellite DNA, designated RrS1, is revealed in Rana ridibunda genomes by the restriction endonuclease Stul, which generates a major repetitive sequence fragment of 300 and a minor one of 200 bp. This AT-rich (68%) satellite family is located at the centromeres of the five largest chromosomes (1-5) and of a medium to small heterobrachial one (8 or 9); it thus constitutes only part of the centromeric heterochromatin that characterizes all Rana ridibunda chromosomes. RrS1 represents about 2.5% of the genome of Rana ridibunda; it may represent as little as 0.2% of the genome of Rana lessonae, and cannot be detected in Xenopus laevis frogs or Salamandra salamandra and Triturus carnifex salamanders. Segments of the satellite sequence are similar to sequences of yeast centromeric DNA element CDEIII and of the mammalian CENP-B box. A role for RrS1 and other centromeric satellite DNAs in the germ line genome exclusion of the hybridogenetic frog hybrids, although suggested, has not yet been demonstrated.

Animals↗
PubMed1977

The ultrastructure of astrocytes, oligodendrocytes, and microglia in the optic nerve of urodele amphibians (A. punctatum, T. pyrrhogaster, T. viridescens).

Recent ultrastructural studies which indicate a single types of glia cell in the amphibian optic nerve are contradicted by the results of the present investigation demonstrating three types of glial cells in the optic nerve of adult newts T. viridescens and T. pyrrbogaster, and the neotenous salamander A. punctatum. Well differentiated astrocytes, oligodendrocytes and microglia are the principal glial constituents with cytological characteristics corresponding to glial elements in the optic nerve of mammals. Immature astrocytes and oligodendrocytes are also present in the nerve indicating continuing production of cells from neuro-ectodermal precursors. Astrocytes constitute approximately 80% of the total. Processes of the large multipolar elements divide axons into bundles and extend to the pial surface to form the glia limitans. A distinct inter-species variability (6--17%) in oligodendrocytes is apparently related to differences in the incidence of myelinated axons. Microglia are the least numerous element constituting only 2--6%. They arise, in part, from monocytic cells near the pial surface.

Ambystoma↗
PubMed1996

When Biologists and Engineers Collide: Habitat Conservation Planning in the Middle of Urbanized Development

/ The City of Austin, Texas, is one of the fastest growing metropolitan areas in the United States. It is also in one of the most biologically diverse terrestrial ecosystems in the world: the Balcones Canyonlands. Five cave invertebrates and two species of birds that inhabit the area are listed as threatened or endangered, two species of plants are candidates for listing, several others are considered rare and of concern, and a species of the salamander has also been proposed for listing. A habitat conservation plan, of "national significance . . ." according to Secretary of Interior Bruce Babbit (Haurwitz 1996), has been under development for the last several years to conserve those endangered species through a 2400-ha system of preserves and to allow development to continue in more than 162,000 ha of surrounding area. The preserve system, comprising several units ranging in size from less than a hundred to several thousand hectares, would be bordered in many instances by developed areas. Development and maintenance of the infrastructure necessary for new and existing development, both commercial and residential, could have negated the biological value of the preserves (e.g., power-line corridors, water-treatment pipelines and facilities). The challenge of bringing this plan to fruition illustrates the complex biological, technical, and sociological context within which habitat conservation planning may occur. Resolving resource use conflicts of this nature have several commonalities that overarch these contexts. If recognized and addressed, one may move easily and foster positive results. These commonalities can be expressed as principles such as: relying on scientists to recognize, but not solve problems; acting before a scientific consensus is achieved; including human motivation and responses as part of the system to be studied and managed; and confronting uncertainty.KEY WORDS: Endangered species; Habitat conservation plan; Resource conflicts; Biologists; Engineers

Journal Article↗
PubMed1976

Effect of calcium on the membrane potential of Amphiuma red cells.

An increase in extracellular Ca concentration causes the membrane of giant red cells of the salamander, Amphiuma means, to undergo a marked, transient hyperpolarization. This hyperpolarization is caused by an increase in K permeability of the membrane as judged from the K sensitivity of the membrane potential and from the rate of K loss under influence of raised extracellular Ca concentration. At constant external pH, the induction of hyperpolarization by increased extracellular Ca has a relatively well-defined threshold concentration. Furthermore the phenomenon is of an "all or none" type with most of the cells having membrane potential values either in the normal range (about -15 mV) or in the range -40 to -70mV. Shortly after suspension in Ringer's with 15 mm Ca, most if not all of the individual cells are hyperpolarized. Upon continued exposure (5-20 min) to the higher Ca concentration the membrane potential returns to the normal value in a fashion compatible with an "all or none" response. The observed Ca effect is sensitive to the pH of the suspending medium. At pH 6.2 the response is absent whereas the hyperpolarization is markedly stronger at pH 8.2 than at PH 7.2. It is argued that a reliable transport number for K under influence of Ca cannot be estimated from the slope of membrane potential vs. log (extracellular K concentration). This is probably related to the fact that the membrane potentials of the cells in the population do not stay constant in time. The above phenomenon is compared with the Ca-induced K permeability in poisoned human red cells or red cell ghosts. It is important to note that the cells employed in the present study are neither poisoned nor mechanically disrupted. This study emphasizes that the role of Ca in regulating cell membrane permeability to K seems to be a general feature.

Animals↗
PubMed1981

Na-pump sites in the oviduct of Salamandra salamandra (L.) (Amphibia, Urodela).

Using 3H-ouabain autoradiography, Na+-K+-ATPase has been localized on the basolateral membranes of ciliated and nonciliated cells in the oviduct (pars recta, p. convoluta I, II, III) of the European fire salamander, Salamandra salamandra. The mucous and seromucous gland cells of the p. convoluta I, II, III, however, do not show any significant labelling. An asymmetrical distribution of ouabain binding sites is a main feature of transporting epithelia.

Animals↗
PubMed1994

Tetrodotoxin-resistant sodium channels.

1. Tetrodotoxin (TTX) has been widely used as a chemical tool for blocking Na+ channels. However, reports are accumulating that some Na+ channels are resistant to TTX in various tissues and in different animal species. Studying the sensitivity of Na+ channels to TTX may provide us with an insight into the evolution of Na+ channels. 2. Na+ channels present in TTX-carrying animals such as pufferfish and some types of shellfish, frogs, salamanders, octopuses, etc., are resistant to TTX. 3. Denervation converts TTX-sensitive Na+ channels to TTX-resistant ones in skeletal muscle cells, i.e., reverting-back phenomenon. Also, undifferentiated skeletal muscle cells contain TTX-resistant Na+ channels. Cardiac muscle cells and some types of smooth muscle cells are considerably insensitive to TTX. 4. TTX-resistant Na+ channels have been found in cell bodies of many peripheral nervous system (PNS) neurons in both immature and mature animals. However, TTX-resistant Na+ channels have been reported in only a few types of central nervous system (CNS). Axons of PNS and CNS neurons are sensitive to TTX. However, some glial cells have TTX-resistant Na+ channels. 5. Properties of TTX-sensitive and TTX-resistant Na+ channels are different. Like Ca2+ channels, TTX-resistant Na+ channels can be blocked by inorganic (Co2+, Mn2+, Ni2+, Cd2+, Zn2+, La3+) and organic (D-600) Ca2+ channel blockers. Usually, TTX-resistant Na+ channels show smaller single-channel conductance, slower kinetics, and a more positive current-voltage relation than TTX-sensitive ones. 6. Molecular aspects of the TTX-resistant Na+ channel have been described. The structure of the channel has been revealed, and changing its amino acid(s) alters the sensitivity of the Na+ channel to TTX. 7. TTX-sensitive Na+ channels seem to be used preferentially in differentiated cells and in higher animals instead of TTX-resistant Na+ channels for rapid and effective processing of information. 8. Possible evolution courses for Na+ and Ca2+ channels are discussed with regard to ontogenesis and phylogenesis.

Animals↗
PubMed1996

Injury-induced remodelling and regeneration of the ribbon presynaptic terminal in vitro.

The neuronal response to axonal injury may relate to the type of insult incurred. Recently, neuritic and presynaptic varicosity regeneration by isolated adult salamander photoreceptors was demonstrated. We have used this system to compare the rod photoreceptor response to two types of injury: denervation/detargeting, the removal of pre- and postsynaptic partners from the axon terminal, and axotomy, the removal of the axon terminal itself. Cells were followed with time-lapse video microscopy for 24-48 h in culture and immunolabelled for SV2 or synaptophysin to identify synaptic vesicle-containing varicosities. Although all injured cells responded with regenerative growth, denervated/detargeted photoreceptors (i.e. neurons which retain their axon terminal) grew 80% more processes and fourfold more presynaptic varicosities than axotomized neurons. In cells which retained their original axon and terminal, varicosity formation generally began with axon retraction. Retraction was followed by elaboration of a lamellipodium and, by 48 h, development of varicosity-bearing neurites from the lamellipodium. Synaptic vesicle protein localization in denervated/detargeted cells paralleled axon terminal reorganization. Axotomized cells, in contrast, lacked synaptic vesicle protein immunoreactivity during this period. To detect synaptic protein synthesis, photoreceptors were examined for colocalization of synaptic vesicle protein with rab6, a Golgi marker, by confocal microscopy. As expected, synaptic vesicle protein staining was present in the Golgi complex during regeneration; however, in cells with an axon, new synaptic vesicle protein-labelled varicosities were found at early stages, prior to the appearance of immunolabel in the Golgi complex. The data demonstrate remarkable plasticity in the ribbon synapse, and suggest that in adult rod cells with an intact axon terminal, synaptic vesicle protein synthesis is not a prerequisite for the formation of new presynaptic-like terminals. We propose that preexisting axonal components are reutilized to expedite presynaptic renewal as an early response to denervation/detargeting.

Ambystoma↗
PubMed1997

Thyroid hormone receptor genes of neotenic amphibians.

Since thyroid hormones play a pivotal role in amphibian metamorphosis we used PCR to amplify DNA fragments corresponding to a portion of the ligand-binding domain of the thyroid hormone receptor (TR) genes in several neotenic amphibians: the obligatory neotenic members of the family Proteidea the mudpuppy Necturus maculosus and Proteus anguinus as well as two members of the facultative neotenic Ambystoma genus: the axolotl Ambystoma mexicanum and the tiger salamander Ambystoma tigrinum. In addition, we looked for TR genes in the genome of an apode Typhlonectes compressicaudus. TR genes were found in all these species including the obligatory neotenic ones. The PCR fragments obtained encompass both the C and E domains and correspond to alpha and beta genes. Their sequences appear to be normal, suggesting that there is no acceleration of evolutionary rates in the TR genes of neotenic amphibians. This result is not surprising for Ambystomatidae, which are known to respond to T3 (3,3',5-triiodothyronine) but is not in agreement with biochemical and biological data showing that Proteidea cannot respond to thyroid hormones. Interestingly, by RT-PCR analysis we observed a high expression levels of TRalpha in gills, intestine, and muscles of Necturus as well as in the liver of Ambystoma mexicanum, whereas TRbeta expression was only detected in Ambystoma mexicanum but not in Necturus. Such a differential expression pattern of TRalpha and TRbeta may explain the neoteny in Proteidea. The cloning of thyroid-hormone-receptor gene fragments from these species will allow the molecular study of their failure to undergo metamorphosis.

Amino Acid Sequence↗
PubMed2002

Sodium absorption, volume control and potassium channels: in tribute to a great biologist.

It is well established, for all Na-absorbing epithelia, that an increase in the rate of transcellular Na+ absorption is accompanied by an increase in the conductance of the basolateral membrane to K+. For the case of small intestinal epithelial cells from the salamander Necturus maculosus, where the rate of transcellular Na+ absorption can be increased manyfold by the addition of sugars or amino acids to the luminal bathing solution, it appears that this parallelism between Na-K pump rate and basolateral membrane K+ conductance is closely related to volume regulation by the enterocyte. Recent studies have disclosed the presence of stretch-activated K+ channels, in a highly enriched basolateral membrane fraction isolated from these epithelial cells, whose activity is increased by an increase in vesicle volume and inhibited by a decrease in vesicle volume or ATP. The activity of this channel also appears to be regulated by the degree of organization of the cortical actin cytoskeleton; activity is increased by depolymerization of the actin cytoskeleton and decreased by repolymerization of that structure. We postulate that the inhibitory effect of ATP is related to its role in promoting the polymerization of G-actin to form F-actin. We propose that enterocyte swelling that results from the intracellular accumulation of sugars or amino acids in osmotically active forms brings about disorganization of the cortical actin cytoskeleton and activates these channels and is, at least in part, responsible for the "pump-leak parallelism" in this amphibian.

Absorption↗