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PubMed1982

A simple method for measuring thickness of the mucus gel layer adherent to rat, frog and human gastric mucosa: influence of feeding, prostaglandin, N-acetylcysteine and other agents.

1. A technique has been developed for measuring thickness of the gastric surface mucus gel layer. Mucosal sections (1.6 mm) were cut from frog and rat stomach and human antrum, mounted transversely and viewed by an inverse microscope (x 200 magnification) under dark field illumination or phase contrast. The mucus layer was readily distinguishable and its dimensions could be recorded by means of an eyepiece graticule. 2. Mean mucus gel thickness in rat, frog was 73, 76, 55 and 192 micrometer respectively. However, there was variation in the average thickness of the gel layer between individual mucosae from the same species (up to twofold). Mucus thickness between adjacent regions of the same mucosal section also varied markedly (up to tenfold). 3. Topical administration of 16,16-dimethylprostaglandin E2 by oral intubation caused a significant increase in thickness in both rat and frog at doses of 5 microgram/ml and 0.5 microgram/ml respectively. Feeding and exposure of the mucosa to N-acetylcysteine (10-20%, w/v) produced variable effects whereas pepsin (1 mg/ml) caused a marked reduction in thickness of the surface gel layer in both rat and frog. 4. The technique provides a rapid and simple method for determining gastrointestinal mucus thickness in relation to mucosal morphology. It is ideally suited for studying the control of mucus secretion and effect of drugs.

16,16-Dimethylprostaglandin E2↗
PubMed1998

Effects of the two somatostatin variants somatostatin-14 and [Pro2, Met13]somatostatin-14 on receptor binding, adenylyl cyclase activity and growth hormone release from the frog pituitary.

Two isoforms of somatostatin from frog brain have been recently characterized, namely somatostatin-14 (SS1) and [Pro2, Met13]somatostatin-14 (SS2). The genes encoding for the precursors of these two somatostatin variants are expressed in hypothalamic nuclei involved in the control of the frog pituitary. The aim of the present study was to investigate the effect of SS1 and SS2 on adenohypophysial cells. Autoradiographic studies using [125I-Tyr, D-Trp8] SS1 as a radioligand revealed that somatostatin binding sites are evenly distributed in the frog pars distalis. The SS2 variant was significantly (P < 0.01) more potent than SS1 in competing with the radioligand (IC50= 1.2 +/- 0.2 and 5.6 +/- 0.6 nM, respectively). Both SS1 and SS2 induced a modest but significant reduction in cAMP formation in dispersed distal lobe cells but did not affect spontaneous growth hormone (GH) release. Synthetic human GRF (hGRF) induced a significant increase in cAMP accumulation and GH release in this system. Both SS1 and SS2 inhibited the stimulatory effects of hGRF on cAMP formation and GH secretion. These data show that the SS1 and SS2 variants can regulate adenohypophysial functions. The fact that GH cells are exclusively located in the dorsal area of the frog adenohypophysis, while somatostatin receptors are present throughout the pars distalis, indicates that the two somatostatin isoforms may control the secretion of pituitary hormones additional to GH in amphibians.

Adenylyl Cyclases↗
PubMed2003

Palaeoclimatic changes explain Anatolian mountain frog evolution: a test for alternating vicariance and dispersal events.

Holarctic biodiversity has been influenced by climatic fluctuations since the Pliocene. Asia Minor was one of the major corridors for postglacial invasions in the Palearctic. Today this area is characterized by an extraordinarily rich fauna with close affiliation to European, Asian and Indo-African biota. However, exact scenarios of range expansion and contraction are lacking. Using a phylogeographical approach we (i). identify monophyletic lineages among Anatolian mountain frogs and (ii). derive a spatio-temporal hypothesis for the invasion process in Anatolia. We sequenced 540 bp of the mitochondrial 16S rRNA gene from 40 populations of mountain frogs from Anatolia, the Elburz Mountains and the Caucasus. Our samples comprise all known species and subspecies: Rana macrocnemis macrocnemis, R. m. tavasensis, R. m. pseudodalmatina, R. camerani and R. holtzi. They include the type localities of four of these taxa. We used a nested clade analysis (NCA) to infer historical and recurrent events that account for the observed geographical distribution of haplotypes. None of the extant species is monophyletic. Based on a molecular clock calibration using homologous sequences of Western Palearctic water frogs of the same genus, we estimated that a basic radiation into three lineages c. 2 Mya was followed by several dispersal and fragmentation events. The geographical distribution of resident and widespread haplotypes allows us to infer and date scenarios of range expansion and fragmentation that are aligned with dramatic climatic oscillations that have occurred during the last 600000 years. Consequently, Pliocene and Pleistocene climatic oscillations triggered the evolution of Anatolian mountain frogs through an interplay of vicariance and dispersal events.

Animals↗
PubMed1998

Possible role of serotonin in Merkel-like basal cells of the taste buds of the frog, Rana nigromaculata.

Merkel-like basal cells in the taste buds of the frog were examined by fluorescence histochemistry, immunohistochemistry and electron microscopy. There were about 16-20 basal cells arranged in a radial fashion at the base of each taste bud. These cells were strongly immunopositive for serotonin antiserum. They were characterised by the presence of numerous dense-cored granules in the cytoplasm ranging from 80 to 120 nm in diameter, and of microvilli protruding from the cell surface. For 4 mo after sensory denervation by cutting the gustatory nerves, all cell types of the taste bud were well preserved and maintained their fine structure. Even at 4 mo after denervation, the basal cells exhibited a strong immunoreaction with serotonin antiserum. To investigate the function of serotonin in the basal cells in taste bud function, serotonin deficiency was induced by administration of p-chlorophenylalanine (PCPA), an inhibitor of tryptophan hydroxylase, and of p-chloroamphetamine (PCA), a depletor of serotonin. After administration of these agents to normal and denervated frogs for 2 wk, a marked decrease, or complete absence, of immunoreactivity for serotonin was observed in the basal cells. Ultrastructurally, degenerative changes were observed in both types of frog; numerous lysosome-like myelin bodies were found in all cell types of the taste buds. The number of dense-cored granules in the basal cells also was greatly decreased by treatment with these drugs. Serotonin in Merkel-like basal cells appears to have a trophic role in maintenance of the morphological integrity of frog taste bud cells.

Animals↗
PubMed1996

In vivo and in vitro evidence for the biosynthesis of testosterone in the telencephalon of the female frog.

Neurons and glial cells are capable of synthesizing various steroid hormones, but biosynthesis of testosterone in the CNS has never been reported. The aim of the present study was to demonstrate the synthesis of testosterone in the frog brain. The presence of 17beta-hydroxysteroid dehydrogenase (17beta-HSD)-like immunoreactivity was detected in a population of glial cells located in the telencephalon. Reversed-phase HPLC analysis of brain tissue extracts combined with radioimmunoassay detection revealed the presence of substantial amounts of testosterone and 5alpha-dihydrotestosterone (5alpha-DHT) in the telencephalon where 17beta-HSD-positive cells were visualized. In male frogs, castration totally suppressed testosterone and 5alpha-DHT in the blood and in the rhombencephalon but did not affect the concentration of these two steroids in the telencephalon. Chemical characterization of testosterone in female frog telencephalon extracts was performed by coupling HPLC analysis with gas chromatography-mass spectrometry. Using the pulse-chase technique with [3H]pregnenolone as a precursor, the formation of a series of metabolites was observed, including dehydroepiandrosterone, androstenedione, testosterone, 5alpha-DHT, and estradiol. These data demonstrate the existence of an active form of 17beta-HSD in the frog telencephalon, which is likely involved in testosterone biosynthesis within the brain.

17-Hydroxysteroid Dehydrogenases↗
PubMed2006

Leptin (ob gene) of the South African clawed frog Xenopus laevis.

Leptin, the protein product of the obese (ob) gene, is a type-I cytokine hormone secreted by fat that is integral to food intake regulation and influences almost every physiological system in juvenile and adult mammals. Since the identification of leptin in the mouse in 1994, biologists have searched for orthologous genes in other species with limited success. In this article, we report the identification and functional characterization of leptin and leptin receptor (LR) in Xenopus. Despite low amino acid sequence similarity to mammalian leptins ( approximately 35%) the frog protein has a nearly identical predicted tertiary structure and can activate the frog and mouse LRs in vitro. We showed that recombinant frog leptin (rxLeptin) is a potent anorexigen in frogs, as it is in mammals, but this response does not develop until midprometamorphosis. However, during early prometamorphosis, exogenous rxLeptin induced growth and development of the hind limb, where LR mRNA is expressed. The rxLeptin also stimulated cell proliferation in cultured hind limbs from early prometamorphic tadpoles, as measured by [(3)H]thymidine uptake. These findings are evidence that leptin can influence limb growth and differentiation during early development. Furthermore, the isolation and characterization of leptin and its receptor in a nonamniote provides an essential foundation for elucidating the structural and functional evolution of this important hormone.

Amino Acid Sequence↗
PubMed2001

The evolution of coloration and toxicity in the poison frog family (Dendrobatidae).

The poison frogs (family Dendrobatidae) are terrestrial anuran amphibians displaying a wide range of coloration and toxicity. These frogs generally have been considered to be aposematic, but relatively little research has been carried out to test the predictions of this hypothesis. Here we use a comparative approach to test one prediction of the hypothesis of aposematism: that coloration will evolve in tandem with toxicity. Recently, we developed a phylogenetic hypothesis of the evolutionary relationships among representative species of poison frogs, using sequences from three regions of mitochondrial DNA. In our analysis, we use that DNA-based phylogeny and comparative analysis of independent contrasts to investigate the correlation between coloration and toxicity in the poison frog family (Dendrobatidae). Information on the toxicity of different species was obtained from the literature. Two different measures of the brightness and extent of coloration were used. (i) Twenty-four human observers were asked to rank different photos of each different species in the analysis in terms of contrast to a leaf-littered background. (ii) Color photos of each species were scanned into a computer and a computer program was used to obtain a measure of the contrast of the colors of each species relative to a leaf-littered background. Comparative analyses of the results were carried out with two different models of character evolution: gradual change, with branch lengths proportional to the amount of genetic change, and punctuational change, with all change being associated with speciation events. Comparative analysis using either method or model indicated a significant correlation between the evolution of toxicity and coloration across this family. These results are consistent with the hypothesis that coloration in this group is aposematic.

Amphibian Venoms↗
PubMed1971

Absence of adaptive modification in developing retinotectal connections in frogs after visual deprivation or disparate stimulation of the eyes.

Action potentials evoked in the tectum by visual stimulation of the ipsilateral eye were absent in frog larvae and developed during metamorphosis. Formation of the connections underlying these responses is not based on the animal's visual experience. The development of the ipsilateral retinotectal projection occurred normally in frogs reared through metamorphosis in the dark from midlarval stages to adults. Inversion of one eye of frog larvae did not affect the development of ipsilateral retinotectal projections, which developed according to the inherent correspondences between the retinae regardless of the disparities produced by changing the relative positions of the eyes. No compensatory changes occurred in the retinotectal projections in response to the surgical derangement. Skin grafts completely occluding one eye, which were made at early larval stages and left in place for up to 88 days, did not affect the development of normal ipsilateral retinotectal connections. However, abnormal ipsilateral tectal responses evoked by stimulation through either the normal eye or the occluded eye were found in adult frogs after occlusion of one eye from larval stages for more than 121 days. It was concluded that visual stimulation is not required for the normal development of ipsilateral retinotectal connections but is required for their long-term maintenance.

Action Potentials↗
PubMed1972

Calf crystallin synthesis in frog cells: the translation of lens-cell 14S RNA in oocytes.

14S RNA isolated from calf-lens polyribosomes was injected into oocytes of the frog Xenopus laevis. Oocytes injected with 14S RNA and buffer contained a protein resembling the A2 chain of calf alpha-crystallin; oocytes injected with buffer alone contained no crystallin-like material. alphaA2 crystallin polypeptides were identified by various criteria: urea-gel electrophoresis under acidic and basic conditions, gel electrophoresis in sodium dodecyl sulfate, N-terminal analysis, and paper chromatography of methionine-containing tryptic peptides. It is concluded that when it is injected into a living frog oocyte, the 14S RNA from lens tissue is reasonably stable and has the properties of an alphaA2 crystallin messenger. The messenger requires no lens cell-specific components for translation within the oocyte, and the translational machinery of the frog cell will accept messenger RNA from a totally different cell type from another species. The A2 chains of alpha-crystallin extracted from lens tissue possess an acetylated N-terminal methionine residue; the N-terminal methionine of alphaA2 chains derived from frog oocytes injected with 14S RNA was also acetylated.

Acrylamides↗
PubMed1981

Transformation of frog embryos with a rabbit beta-globin gene.

In order to study the fate and possible expression of foreign DNA during embryogenesis of the frog Xenopus laevis, we have injected a rabbit beta-globin gene into fertilized Xenopus eggs. Frog embryo DNA was extracted at various stages of development, fractionated by agarose gel electrophoresis, transferred to nitrocellulose filters, and hybridized to labeled beta-globin recombinant plasmid DNA. It was found that the injected DNA replicated extrachromosomally, reaching, at gastrula stage, a level equivalent to a 10- to 200-fold amplification of input DNA. At later stages, a majority of the foreign DNA was degraded, but a small fraction was maintained. Six-week-old tadpoles as well as six-month-old frogs contained an average of 3-10 copies of the rabbit globin gene per cell. Most of these persisting globin genes were present as long tandem repeats and comigrated in agarose gel electrophoresis with high molecular weight Xenopus DNA. Analysis of globin gene expression by S1 nuclease mapping showed that the rabbit beta-globin promoter was recognized in the frog embryo and that the transcripts were correctly spliced.

Animals↗
PubMed1994

Frog diazepam-binding inhibitor: peptide sequence, cDNA cloning, and expression in the brain.

Three peptides derived from diazepam-binding inhibitor (DBI) were isolated in pure form from the brain of the frog Rana ridibunda. The primary structures of these peptides showed that they correspond to mammalian DBI-(1-39), DBI-(58-87), and DBI-(70-87). A set of degenerate primers, whose design was based on the amino acid sequence data, was used to screen a frog brain cDNA library. The cloned cDNA encodes an 87-amino acid polypeptide, which exhibits 68% similarity with porcine and bovine DBI. Frog DBI contains two paired basic amino acids (Lys-Lys) at positions 14-15 and 62-63 and a single cysteine within the biologically active region of the molecule. Northern blot analysis showed that DBI mRNA is expressed at a high level in the brain but is virtually absent in peripheral tissues. The distribution of DBI mRNA and DBI-like immunoreactivity in the frog brain was studied by in situ hybridization and immunocytochemistry. Both approaches revealed that the DBI gene is expressed in ependymal cells and circumventricular organs lining the ventricular cavity. Since amphibia diverged from mammals at least 250 million years ago, the data show that evolutionary pressure has acted to conserve the structure of DBI in the vertebrate phylum. The distribution of both DBI mRNA and DBI-like immunoreactivity indicates that DBI is selectively expressed in glial cells.

Amino Acid Sequence↗
PubMed2000

Overexpression of Xenopus laevis growth hormone stimulates growth of tadpoles and frogs.

The role of growth hormone (GH) in amphibian metamorphosis is ambiguous based on experiments in which mammalian GH was administered to tadpoles and frogs. We have reexamined the effects of GH by producing transgenic Xenopus laevis that overexpress the cDNA encoding X. laevis GH. These transgenic tadpoles take the same length of time to reach metamorphosis as control tadpoles, but the transgenic tadpoles are twice as large. After metamorphosis, the transgenic frogs grow at a greatly accelerated rate and develop skeletal abnormalities reminiscent of acromegaly. The transgenic frogs are larger than mature frogs in a few months and die in about 1 year. At as early as 10 months of age, the males have mature sperm. We conclude that the growth-promoting effects of GH in this amphibian closely resemble those described for mammals. Although excess GH increases the size of the tadpole, it does not alter the developmental programs involved in metamorphosis.

Animals↗
PubMed2005

Archaeobatrachian paraphyly and pangaean diversification of crown-group frogs.

Current models for the early diversification of living frogs inferred from morphological, ontogenetic, or DNA sequence data invoke very different scenarios of character evolution and biogeography. To explore central controversies on the phylogeny of Anura, we analyzed nearly 4000 base pairs of mitochondrial and nuclear DNA for the major frog lineages. Likelihood-based analyses of this data set are congruent with morphological evidence in supporting a paraphyletic arrangement of archaeobatrachian frogs, with an (Ascaphus + Leiopelma) clade as the sister-group of all other living anurans. The stability of this outcome is reinforced by screening for phylogenetic bias resulting from site-specific rate variation, homoplasy, or the obligatory use of distantly related outgroups. Twenty-one alternative branching and rooting hypotheses were evaluated using a nonparametric multicomparison test and parametric bootstrapping. Relaxed molecular clock estimates situate the emergence of crown-group anurans in the Triassic, approximately 55 million years prior to their first appearance in the fossil record. The existence of at least four extant frog lineages on the supercontinent Pangaea before its breakup gains support from the estimation that three early splits between Laurasia- and Gondwana-associated families coincide with the initial rifting of these landmasses. This observation outlines the potential significance of this breakup event in the formation of separate Mesozoic faunal assemblages in both hemispheres.

Animals↗
PubMed2006

Uptake and elimination of naphthalene from liver, lung, and muscle tissue in the leopard frog (Rana pipiens).

The effects of a 0-12-hour naphthalene exposure on pulmonary CO(2) excretion and bioaccumulation in the leopard frog, Rana pipiens, were investigated. The data showed that naphthalene transport occurred from the aqueous phase into the frog tissue. The first-order rate constant (k in day-1) for the entry of naphthalene from the water into the frog was 0.079 +/- 0.007 (k +/- 95% C.I.). Bioaccumulation of naphthalene was measured in liver, lung, and thigh muscle tissue. Exposure to naphthalene caused a significant reduction in pulmonary CO(2) excretion, particularly following the first 30 minutes of exposure. Pulmonary CO(2) excretion returned to baseline levels after 8 hours of exposure, indicating that some degree of acclimation had occurred. Depuration experiments were used to monitor recovery from naphthalene exposure. Recovery of CO(2) excretion was evident following 2 hours of depuration and complete elimination of naphthalene from tissues occurred after 3 hours. The data indicate that accumulated polycyclic aromatic hydrocarbons (PAHs) may alter normal physiologic functions such as gas exchange. Since amphibians, such as frogs, are one of the first organisms to come into contact with contaminated water and sediments, the information in this study suggests that this species may be used to assess bioaccumulation and toxicity of PAHs in ecosystems.

Animals↗
PubMed1997

Transplantation of quail collagen-tailed acetylcholinesterase molecules onto the frog neuromuscular synapse.

The highly organized pattern of acetylcholinesterase (AChE) molecules attached to the basal lamina of the neuromuscular junction (NMJ) suggests the existence of specific binding sites for their precise localization. To test this hypothesis we immunoaffinity purified quail globular and collagen-tailed AChE forms and determined their ability to attach to frog NMJs which had been pretreated with high-salt detergent buffers. The NMJs were visualized by labeling acetylcholine receptors (AChRs) with TRITC-alpha-bungarotoxin and AChE by indirect immunofluorescence; there was excellent correspondence (>97%) between the distribution of frog AChRs and AChE. Binding of the exogenous quail AChE was determined using a species-specific monoclonal antibody. When frog neuromuscular junctions were incubated with the globular G4/G2 quail AChE forms, there was no detectable binding above background levels, whereas when similar preparations were incubated with the collagen-tailed A12 AChE form >80% of the frog synaptic sites were also immunolabeled for quail AChE attached. Binding of the A12 quail AChE was blocked by heparin, yet could not be removed with high salt buffer containing detergent once attached. Similar results were obtained using empty myofiber basal lamina sheaths produced by mechanical or freeze-thaw damage. These experiments show that specific binding sites exist for collagen-tailed AChE molecules on the synaptic basal lamina of the vertebrate NMJ and suggest that these binding sites comprise a "molecular parking lot" in which the AChE molecules can be released, retained, and turned over.

Acetylcholinesterase↗
PubMed1968

The ultrastructure of frog ventricular cardiac muscle and its relationship to mechanism of excitation-contraction coupling.

Frog ventricular cardiac muscle has structural features which set it apart from frog and mammalian skeletal muscle and mammalian cardiac muscle. In describing these differences, our attention focused chiefly on the distribution of cellular membranes. Abundant inter cellular clefts, the absence of tranverse tubules, and the paucity of sarcotubules, together with exceedingly small cell diameters (less than 5 micro), support the suggestion that the mechanism of excitation-contraction coupling differs in these muscle cells from that now thought to be characteristic of striated muscle such as skeletal muscle and mammalian cardiac muscle. These structural dissimilarities also imply that the mechanism of relaxation in frog ventricular muscle differs from that considered typical of other striated muscles. Additional ultrastructural features of frog ventricular heart muscle include spherical electron-opaque bodies on thin filaments, inconstantly present, forming a rank across the I band about 150 mmicro from the Z line, and membrane-bounded dense granules resembling neurosecretory granules. The functional significance of these features is not yet clear.

Animals↗
PubMed1979

Freeze-fracture evidence for the presence of cholesterol in particle-free patches of basal disks and the plasma membrane of retinal rod outer segments of mice and frogs.

The freeze-fracture technique was used to examine the membranes of the photoreceptors of mice and frogs. Particle-free patches were found in the plasma membrane and basal disk membranes of the outer segments of both mice and frogs housed at room temperature, but not in frogs kept in a cold room. These patches were shown not to be artifacts of cryoprotection or fixation, and they persisted when fresh isolated outer segments were frozen by an ultrarapid method. They were also found to persist in mouse rods when retinas were incubated and subsequently fixed at temperatures up to 80 degrees C. Cholesterol was implicated as a significant component of the patches by the observation that, in the outer segments, pits, induced by treatment with the sterol-specific polyene antibiotic filipin, were present in and confined to the particle-free patches. That these lesions are not inherently limited to particle-free membrane areas was evident in the apical plasma membrane of the photoreceptor inner segments, where particles and pits were intermixed. Treatment with saponin, a surface-active agent which specifically complexes cholesterol, resulted in the disappearance of the particle-free patches. Patches were found in basal disks of both mouse and frog rods but not in older disks nearer the pigment epithelium, which indicates that changes occur in the composition of disk membranes and/or in the molecular ordering of their protein and lipid components during the early phase of their transit from the base towards the apex of the outer segment.

Animals↗
PubMed1955

Electrolyte distribution and active salt uptake in frog skin.

1. The "chloride space" in frog skin was determined and found to be 69.7 per cent by weight of wet skin. The chloride space occupies about 94 per cent of the total water space of skin. From this and other information, it appears that the "non-chloride space" measures only a part of the space occupied by the structural elements of skin. This space is referred to here as the intracellular compartment and the remainder as the extracellular compartment of frog skin. On this basis, potassium and sodium in skin are distributed as follows: total sodium, 60 to 75 microeq./gm. of wet skin; all sodium is probably extracellular; total potassium, 39 to 49 microeq./gm.; intracellular potassium, 37 to 47 microeq./gm. 2. Skins were immersed in solutions differing from each other in their sodium and potassium concentrations. Three levels of NaCl were studied: 48, 119, and 169 microeq./ml. For each of these solutions (referred to below as diluted, physiological, and concentrated saline), the potassium levels were varied from 0.1 to 20 microeq./ml. For skins in solutions low in potassium and high in sodium, it was found that an exchange of intracellular potassium against extracellular sodium occurs. The ratio for the number of potassium ions lost/number of sodium ions gained was 4:1,4:6, and 4:8 for skin in K(+)-free diluted, physiological, and concentrated saline, respectively. 3. Uptake of NaCl by the epithelium of frog skin is dependent on the potassium concentration of the environment. For skins in physiological saline, net uptake of NaCl was optimal (0.90 microeq. x cm.(-2) x hr.(-1)) at 1 to 5 microeq. K(+)/ml. For skins in diluted and concentrated saline optimal NaCl uptake was seen at potassium concentrations of approximately 5 and 10 microeq. K(+)/ml., respectively. Net uptake of NaCl by the skin is also discussed, with relation to the potassium balance of skin. 4. Skin potentials decreased with increasing extracellular potassium concentration when diluted saline solutions were used. The opposite of this was found for skins in concentrated saline. For skins in physiological saline, skin potentials rose sharply from rather low values, when placed in solutions very low in potassium, to relatively high values, when immersed in solutions containing 1 to 5 microeq. K(+)/ml. Further increase in potassium concentration of the bath led to slight reductions in skin potentials. The highest potentials observed were of the order of 40 mv. In all cases studied, the inside was positive with relation to the outside. 5. It can be shown that values for intracellular potassium concentration as a function of extracellular potassium concentration satisfy, at a first but good approximation, Freundlich's isotherm. A modification of Freundlich's isotherm, recently introduced by Sips, may also be used to correlate the experimental data quantitatively. Since the latter isotherm has a rational interpretation, it is suggested that this be used, rather than Freundlich's isotherm, to express quantitatively the dependence of intracellular on extracellular potassium in frog skin.

Animals↗