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PubMed1973

Influence of transepithelial potential difference on the sodium uptake at the outer surface of the isolated frog skin.

The unidirectional uptake of sodium across the outer surface of the isolated frog skin (J(12) (Na)) was measured in the presence of transepithelial potential difference (Delta(psi)) ranging from +100 to -100 mV. With a sodium concentration of 115 mM in the bathing solutions J(12) (Na) increases significantly when the spontaneous Delta(psi) is reduced to zero by short-circuiting the skin. With an Na concentration of 6 mM a progressive increase J(12) (Na) can be observed when Delta(psi) is decreased in several steps from +100 to -100 mV (serosal side positive and negative, respectively). The observed change J(12) (Na) amounts to a fraction only of that predicted from the shift in Delta(psi). The results suggest that under open circuit conditions the potential step across the outside surface is at most one half of Delta(psi) and that the resistance across the outside and inside barrier of the skin is ohmic. This is in agreement with measurements of intracellular potentials in the frog skin and with resistance measurements carried out in the toad skin. The data strongly support the view that the saturating component of J(psi) proceeds via a charged carrier system. Exposure to negative values of Delta(psi) of 50 mV or more for times of 24 min or more result in a marked reduction of J(12) (Na) which shows only partial or no reversibility.

Amiloride↗
PubMed1988

Trypanosomes of Bufo americanus from northern Michigan.

Two hundred one American toads (Bufo americanus) from northern Michigan were examined for blood trypanosomes. Three species, Trypanosoma bufophlebotomi, T. schmidti-like sp. and T. pseudopodia, had prevalences of 27, 16 and 1%, respectively. Cross experimental inoculations showed that T. bufophlebotomi from toads is not the same as T. ranarum found in frogs of the family Ranidae of this region.

Animals↗
PubMed2004

Novel phylogenetic relationships of the enigmatic brevicipitine and scaphiophrynine toads as revealed by sequences from the nuclear Rag-1 gene.

Owing to a general paucity of characters and an apparently high level of homoplasy, the systematics of frogs have remained disputed. A phylogeny based on the single-copy nuclear Rag-1 gene revealed unexpected placements of scaphiophrynine and brevicipitine toads. The former have usually been considered as sister group to all other extant microhylids or are even classified as a separate family. Their basal position among microhylids was weakly indicated in our analysis; but they clearly are part of a strongly supported clade composed of representatives from five other microhylid subfamilies. By contrast, the brevicipitines, a group that hitherto was unanimously considered to belong to the Microhylidae, were highly divergent and placed as a sister group to the arthroleptoid clade. These novel phylogenetic placements are best reflected by a classificatory status of the Scaphiophryninae as a subfamily of the Microhylidae, whereas the brevicipitines may merit recognition as a distinct family. Our findings seem to corroborate a high degree of morphological homoplasy in frogs and suggest that even highly derived morphological states, such as the hydrostatic tongue of microhylids, hemisotids and brevicipitines, may be subject to convergent evolution, parallelism or character reversal.

Animals↗
PubMed2002

Comparison of isometric contractile properties in hindlimb extensor muscles of the frogs Rana pipiens and Bufo marinus: functional correlations with differences in hopping performance.

The leopard frog (Rana pipiens) is an excellent jumper that can reach high take-off velocities and accelerations. It is diurnal, using long, explosive jumps to capture prey and escape predators. The marine toad (Bufo marinus) is a cryptic, nocturnal toad, typically using short, slow hops, or sometimes walking, to patrol its feeding area. Typical of frogs with these different locomotor styles, Rana has relatively long hindlimbs and large (by mass) hindlimb extensor muscles compared to Bufo. We studied the isometric contractile properties of their extensor muscles and found differences that correlate with their different hopping performances. At the hip (semimembranosus, SM), knee (peroneus, Per) and ankle (plantaris longus, PL), we found that Rana's muscles tended to produce greater maximum isometric force relative to body mass, although the difference was significant only for PL. This suggests that differences in force capability at the ankle may be more important than at other joints to produce divergent hopping performances. Maximum isometric force scaled with body mass so that the smaller Rana has relatively larger muscles and force differences between species may reflect size differences only. In addition, Rana's muscles exhibited greater passive resistance to elongation, implying more elastic tissue is present, which may amplify force at take-off due to elastic recoil. Rana's muscles also achieved a higher percentage of maximum force at lower stimulus inputs (frequencies and durations) than in Bufo, perhaps amplifying the differences in force available for limb extension during natural stimulation. Twitch contraction and relaxation times tended to be faster in Rana, although variation was great, so that differences were significant only for Per. Fatigability also tended to be greater in Rana muscles, although, again, values reached significance in only one muscle (PL). Thus, in addition to biomechanical effects, differences in hopping performance may also be determined by diverse physiological properties of the muscles.

Animals↗
PubMed2002

Lamina-associated polypeptide 2 (LAP2) expression in fish and amphibians.

Somatic and germinal cells of 15 fish and 33 amphibian species were examined by SDS-PAGE followed by immunoblotting to determine the expression of LAP2 (lamina-associated polypeptide 2). LAP2 expression in frogs, salamanders and fish does not vary with the mode of reproduction. In fish and frog cells, a rim-like LAP2 positive region was detected around the nucleus by indirect immunofluorescence microscopy. The cell distribution and expression patterns of LAP2 in fish, frogs and salamanders are comparable with those found in Xenopus and zebrafish. The mammalian somatic cell pattern, which may also occur in gymnophione amphibians, includes LAP2alpha, beta and gamma as major isoforms, whereas LAP2alpha does not occur in cells of fish, frogs and salamanders. In fish, LAP2gamma is the major isoform of somatic cells, suggesting that LAP2gamma may be ancestral. However, in the rainbow trout, as in frogs and salamanders, LAP2beta was the major somatic isoform. Fish and frog sperm only express low molecular weight polypeptides. In contrast, fish and frog oocytes express an oocyte-specific LAP2 isoform of high molecular weight. In the toad Bufo marinus this isoform becomes upregulated in pre-vitellogenic oocytes of 150-200 microm in diameter. The absence of LAP2alpha and the differential expression of LAP2 isoforms in somatic and germ cells, as found in fish and frogs, may be ancestral vertebrate characters. In spite of differences in developmental time, the LAP2 isoforms of somatic cells are upregulated during gastrulation, suggesting that LAP2 may be implicated in the early development of fish and frog.

Animals↗
PubMed2006

Amphibian embryo and parental defenses and a larval predator reduce egg mortality from water mold.

Water molds attack aquatic eggs worldwide and have been associated with major mortality events in some cases, but typically only in association with additional stressors. We combined field observations and laboratory experiments to study egg stage defenses against pathogenic water mold in three temperate amphibians. Spotted salamanders (Ambystoma maculatum) wrap their eggs in a protective jelly layer that prevents mold from reaching the embryos. Wood frog (Rana sylvatica) egg masses have less jelly but are laid while ponds are still cold and mold growth is slow. American toad (Bufo americanus) eggs experience the highest infection levels. They are surrounded by thin jelly and are laid when ponds have warmed and mold grows rapidly. Eggs of all three species hatched early when infected, yielding smaller and less developed hatchlings. This response was strongest in B. americanus. Precocious hatching increased vulnerability of wood frog hatchlings to invertebrate predators. Finally, despite being potential toad hatchling predators, R. sylvatica tadpoles can have a positive effect on B. americanus eggs. They eat water mold off infected toad clutches, increasing their hatching success.

Ambystoma↗
PubMed2001

Identification and characterization of a novel family of mammalian ependymin-related proteins (MERPs) in hematopoietic, nonhematopoietic, and malignant tissues.

Evidence is presented for a family of mammalian homologs of ependymin, which we have termed the mammalian ependymin-related proteins (MERPs). Ependymins are secreted glycoproteins that form the major component of the cerebrospinal fluid in many teleost fish. We have cloned the entire coding region of human MERP-1 and mapped the gene to chromosome 7p14.1 by fluorescence in situ hybridization. In addition, three human MERP pseudogenes were identified on chromosomes 8, 16, and X. We have also cloned the mouse MERP-1 homolog and an additional family member, mouse MERP-2. Then, using bioinformatics, the mouse MERP-2 gene was localized to chromosome 13, and we identified the monkey MERP-1 homolog and frog ependymin-related protein (ERP). Despite relatively low amino acid sequence conservation between piscine ependymins, toad ERP, and MERPs, several amino acids (including four key cysteine residues) are strictly conserved, and the hydropathy profiles are remarkably alike, suggesting the possibilities of similar protein conformation and function. As with fish ependymins, frog ERP and MERPs contain a signal peptide typical of secreted proteins. The MERPs were found to be expressed at high levels in several hematopoietic cell lines and in nonhematopoietic tissues such as brain, heart, and skeletal muscle, as well as several malignant tissues and malignant cell lines. These findings suggest that MERPs have several potential roles in a range of cells and tissues.

Amino Acid Sequence↗
PubMed1992

Conductive chloride flux across amphibian skin: inhibition by indacrinone and cobalt ion.

When amphibian skin was incubated under conditions in which transepithelial sodium transport was abolished, a conductive transepithelial Cl- flux arose when Cl- was removed from one of the compartments. This flux was matched by short-circuit current and it accounted entirely for transepithelial conductance. Cl- influx was larger than efflux; it was linearly related to the magnitude of transepithelial Cl- concentration difference. When applied to the epithelial surface of the tissue, divalent metal cations such as Co2+, and the ethacrynic acid derivative, indacrinone, reduced rapidly and reversibly both transepithelial Cl- (in)flux and short-circuit current. Frog skin proved to be more sensitive to these inhibitors than toad skin. Further characterization of transepithelial Cl- pathway(s) should benefit from the fact that Cl- across amphibian skin can easily be monitored by the short-circuit current method, and from the availability of agents which inhibit this passive flux rapidly and reversibly.

Animals↗
PubMedDate not supplied

Endogenous ouabain-like compound increases heart muscle contractility.

Cardiac glycosides such as digoxin or ouabain have long been known to influence the strength of contraction of cardiac muscle. Although the mechanism of action of these compounds remains unknown, all the proposed modes of action are based on initial binding to specific membrane receptors which are part of the (Na+ + K+)ATPase complex. These receptors, well characterized and defined, suggest the existence of an endogenous substance capable of binding to them, in analogy with endogenous opiates, discovered long after morphine and its receptors. As glycosides affect (Na+ + K+)ATPase activity, an endogenous substance may be a regulator of this important enzyme. Indeed, the search for endogenous regulators of the (Na+ + K+)ATPase or ouabain-like compounds (OLC) has recently intensified. These compounds, extracted and partially purified from mammalian brain, heart, blood and urine, and from toad skin and plasma, have been shown to inhibit 3H-ouabain binding and (Na+ + K+)ATPase activity. We report here that in addition to these effects, the OLC, highly purified from toad skin and sheep brain, increases the force of contraction of frog and guinea pig atrium.

Animals↗
PubMed1998

The binding sites for Xenopus laevis FIII/YY1 in the first exon of L1 and L14 ribosomal protein genes are dispensable for promoter expression.

The genes coding for the ribosomal proteins (rp genes) L14 and L1 in the toad Xenopus laevis are contacted in the first exon by the frog protein, FIII/YY1, homolog of the human zinc-finger protein YY1, acting as repressor, activator and initiator of transcription. To investigate the functional significance of FIII/YY1 in the context of the two rp genes, the L14 region at nucleotide positions -105 to +44, including all of the first exon was linked to the chloramphenicol acetyltransferase (CAT) reporter gene; constructs with wild-type and mutated sites for FIII/YY1 were injected into nuclei of stage V-VI oocytes and analyzed for CAT activity. The same procedure was followed for constructs made with L1 sequences at nucleotide positions -17 to +1567. Mutations in the sites for FIII/YY1 did not change reporter activity, nor did overexpression of FIII/YY1 in the oocytes prior to injection with L1 and L14 constructs. Since oocytes are non-dividing cells, transfections were made of Xenopus kidney cells in culture with the same constructs and the results obtained in oocytes confirmed.

Animals↗
PubMed1974

The compliance of contracting skeletal muscle.

1. The method of controlled releases was used to obtain tension-extension curves in toad (Bufo bufo) sartorii under a variety of conditions at 0 degrees C.2. The curves obtained were approximately linear over a considerable range of force (0.4P(0) to P(0)) if the releases were given from the plateau of tetanic tension. The slope of this linear region was little affected by changes of release velocity in the range 10-120 mm/sec.3. Such changes as did occur with alterations in release velocity could be quantitatively accounted for in terms of the internal shortening predicted by A. V. Hill's two-component model.4. As the muscles were stretched above l(0), we found that the maximum stiffness of the tetanized muscles fell in much the same way as the maximum developed force, P(0).5. In another series of experiments we found a rapid change in the overall shape of the tension-extension curve during the early phase of force development in an isometric tetanus. The stiffness of the muscle increased with increasing developed force during this period.6. The force-velocity curve in these muscles was measured by two methods, both giving a similar result. Surprisingly, toad muscle appears to have about the same intrinsic speed as frog muscle at 0 degrees C. The a.b product from our experiments is considerably greater than the reported values for the maintenance heat rate at 0 degrees C in these muscles.7. The probable site of the variable compliance in active muscle is discussed. It seems most likely that this is within the A-band, perhaps in the cross-bridges themselves.

Animals↗
PubMed2000

Retinylidene proteins: structures and functions from archaea to humans.

Retinylidene proteins, containing seven membrane-embedded alpha-helices that form an internal pocket in which the chromophore retinal is bound, are ubiquitous in photoreceptor cells in eyes throughout the animal kingdom. They are also present in a diverse range of other organisms and locations, such as archaeal prokaryotes, unicellular eukaryotic microbes, the dermal tissue of frogs, the pineal glands of lizards and birds, the hypothalamus of toads, and the human brain. Their functions include light-driven ion transport and phototaxis signaling in microorganisms, and retinal isomerization and various types of photosignal transduction in higher animals. The aims of this review are to examine this group of photoactive proteins as a whole, to summarize our current understanding of structure/function relationships in the best-studied examples, and to report recent new developments.

Amino Acid Sequence↗
PubMed1950

The use of the male California toad in the diagnosis of pregnancy.

The California male toad, readily available in most areas of the state, and for many other reasons a better subject for test purposes than the frog, was used in 237 tests to determine the presence or absence of pregnancy in humans. Human urine was injected into the toads, and the cloacal discharge then was examined for the presence of sperm. There were only two false reactions in the series-both false negative. In subsequent tests in both these cases, the result was positive.

Animals↗