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PubMed1981

The aberrant retino-retinal projection during optic nerve regeneration in the frog. III. Effects of crushing both nerves.

Previous reports from this laboratory have shown that a substantial number of optic axons are misrouted after optic nerve regeneration in the adult frog, Rana pipiens. Regenerating axons from a crushed optic nerve are distributed throughout the opposite nerve. In this study, we report the effect of crushing both optic nerves (double crush) on the pattern and degree of axonal misrouting. In 28 frogs both optic nerves were crushed at the same time (simultaneous double crush) and animals survived for varying periods before the right eye was injected with 3H-proline and the brain processed for autoradiography 24 hours later. In every frog with postoperative survivals longer than 2 weeks, labeled axons from the right eye were found in the left optic nerve. However, when compared to the amount of label seen in frogs in which only the right optic nerve was crushed (single crush) there was substantially less label within the left nerve of frogs after crushing both nerves. Label was also found only at the edge of the left nerve in material from double crush frogs, unlike that found after single crush. In four of six frogs where the left nerve was crushed 1 week after the right nerve (delayed double crush), the proximal end of the left nerve was completely filled with label, but more distally, label was found only along the edge of this nerve. Although fewer optic axons were labeled in the opposite optic nerve of double crush frogs, label did extend to the optic disc of that eye. However, label was not apparent in the ganglion cell fiber layer of the opposite eye. Instead, it was confined to the edge of the optic disc in a space apparently associated with papilledema resulting from crushing the optic nerve of that eye. In six frogs the retina of the left eye was removed at the same time the right optic nerve was crushed. Labeled axons of the right eye filled the left optic nerve to the retina-less shell of the left eye. Thus, these data show that the amount and distribution of axonal misrouting into the opposite optic nerve during optic nerve regeneration is affected by intact or regenerating optic axons from the other eye.

Animals↗

PubMed1991

Quantitative study of the tectally projecting retinal ganglion cells in the adult frog. II. Cell survival and functional recovery after optic nerve transection.

It is known from previous work that ganglion cells disappear from the retina in significant numbers during optic nerve regeneration in the adult frog. In the present study, the population size of surviving ganglion cells that have returned axon terminals to the correct tectal loci was estimated by counts of retrogradely labeled cells in retina-flat-mounts after tectal injections of HRP. Bilaterally symmetric injections were delivered to allow comparison of the normal and affected retinas. The frogs studied had regenerated the left optic nerve and had visually guided behaviors initiated by the recovered eye (see below). The proportion of tectally projecting ganglion cells in the normal retinas and in retinas of normal frogs studied in parallel ranged from 83-86% (Singman and Scalia: J. Comp. Neurol. 302:792-809, 1991). In the affected retinas, the subpopulation of tectally projecting cells was reduced by 40-90% after regeneration, and the relative size of this subpopulation ranged from 67-86%. The optic tectum was injected unilaterally in one specimen, on the side ipsilateral to the regenerated (left) optic nerve. The HRP-labeled ganglion cells in the ipsilateral (left) retina accounted for only 0.8% of the surviving ganglion cells in this animal, whereas it was previously found that the ipsilateral tectally projecting ganglion cells normally amount to 0.9-2.3% (Singman and Scalia, op. cit.) In frogs recovering from transection of the left optic nerve, the frequency, latency, and accuracy of the prey-acquisition responses initiated by the recovering eye were compared with those initiated by the normal eye. Mealworms or lure dummies were used to stimulate prey acquisition. In one experiment, the stimuli were presented unilaterally in the monocular fields of frogs permitted to use both eyes. Prior to the fourteenth postoperative week, the affected eye initiated responses of abnormally long latency and low frequency. In contrast, responses initiated by the affected eye after 14 weeks appeared to be normal in all respects. In another experiment, the normal eye was sutured shut in some frogs recovering for at least 24 weeks and then the affected eye was retested. The affected eye was capable of consistently initiating brisk and accurate prey acquisition. In a final experiment, two stimuli were presented simultaneously in bilaterally symmetric regions of the monocular fields of frogs surviving at least 42 weeks. These fully recovered frogs showed no preference for using either the normal or the recovered eye. Despite severe loss of tectally projecting ganglion cells during optic nerve regeneration, frogs are capable of apparently normal visual responses in prey acquisition tests.

Animals↗

PubMed1980

A comparison of the ability of frog and rat S-9 to activate promutagens in the Ames test.

A mutagenesis assay employing the frog, Rana pipiens, is currently under development [McKinnell et al, 1979]. A question that must be answered is whether the frog is metabolically capable of activating a large number of promutagens. The Ames assay offers a simple means of comparing the metabolism of mutagens by different animal species. The Ames response obtained with frog-liver S-9 was compared to the response with rat-liver S-9, using the following compounds: Benzo(a)pyrene, 7,12-dimethylbenz(a)anthracene, 2-amino-fluorene, azobenzene, Sudan II, dibutylnitrosamine, hydrazine sulfate, hydroxyethylhydrazine, cyclophosphamide, 1,2-dichloroethane, tris(2,3 dibromopropyl)phosphate, diallate, quinoline, quercetin, aflatoxin B 1, emodin, and safrole. Of these compounds, activation by rat S-9 was observed for all except hydrazine sulfate and safrole. All except Sudan II, 1,2-dichloroethane, quinoline, and safrole gave positive Ames responses with frog S-9. In general, the responses with frog S-9 were quantitatively lower than those obtained with Aroclor-induced rat S-9; however, the optimum procedure for frog-liver induction has not been determined. The response to dichloroethane is very sensitive to the amount of activating enzyme present; it might be positive with optimally induced frog S-9. Thus, only two of the 15 compounds positive with rat S-9 were definitely missed when tested with frog S-9. We feel that the frog assay appears to be promising from the standpoint of false-negatives.

Animals↗

PubMed2006

Determination of polychlorinated biphenyl and polycyclic aromatic hydrocarbon elimination rates in adult green and leopard frogs.

The purpose of the present study was to quantify elimination kinetics of polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) in adult green frogs (Rana clamitans) and leopard frogs (Rana pipiens). Three experiments were conducted: PCB elimination rate constants were determined for both frog species, and PAH elimination rate constants were determined for leopard frogs only. In green frogs, significant PCB elimination rate constants ranged from 0.013 to 0.04 d(-1) (time for frogs to achieve 90% steady state with water [t90] = 57.8-178.2 d). In leopard frogs, significant PCB elimination rate constants ranged from 0.004 to 0.047 d(-1) (t90 = 48.8-657.9 d). Polycyclic aromatic hydrocarbon elimination in leopard frogs was faster than PCB elimination in either frog species: Significant PAH rate constants ranged from 0.069 to 0.188 d(-1) (t90 = 12.2-33.5 d). In both species, and for both PCBs and PAHs, a significant inverse relationship was found between the chemical elimination rate constant and Kow. These results show that adult anurans have relatively low elimination rates of PCBs but exhibit a small capacity for metabolic biotransformation of PAHs that is comparable to that of invertebrates but lower than that of fish. These findings suggest that adult amphibians have the potential to be used as biomonitors for persistent organic chemicals.

Animals↗

PubMed2003

A receptor linked to a Gi-family G-protein functions in initiating oocyte maturation in starfish but not frogs.

The stimulation of oocyte maturation by 1-methyladenine in starfish, and by a steroid in frogs, has been proposed to involve G-protein-coupled receptors. To examine whether activation of receptors linked to G(i) or G(z) was sufficient to cause oocyte maturation, we expressed mammalian G(i)- and G(z)-linked receptors in starfish and frog oocytes. Application of the corresponding agonists caused meiosis to resume in the starfish but not the frog oocytes. We confirmed that the receptors were effectively expressed in the frog oocytes by using a chimeric G-protein, G(qi), that converts input from G(i)- and G(z)-linked receptors to a G(q) output and results in a contraction of the oocyte's pigment. These results argue against G(i) or G(z) functioning to cause maturation in frog oocytes. Consistently, maturation-inducing steroids did not cause pigment contraction in frog oocytes expressing G(qi), and G(z) protein was not detectable in frog oocytes. For starfish oocytes, however, our results support the conclusion that G(i) functions in 1-methyladenine signaling and suggest the possibility of using frog oocyte pigment contraction as an assay to identify the 1-methyladenine receptor. To test this concept, we coexpressed G(qi) and a starfish adenosine receptor in frog oocytes and showed that applying adenosine caused pigment contraction.

Animals↗

PubMed1997

Second messenger and cAMP-dependent protein kinase responses to dehydration and anoxia stresses in frogs.

The effects of whole body dehydration (up to 40% of total body water lost) or anoxia exposure (up to 2 days under N2 gas) at 5 degrees C on tissue levels of adenosine 3'-5' cyclic monophosphate (cAMP) and the percentage of cAMP-dependent protein kinase present as the free catalytic subunit (PKAc), as well as the levels of the protein kinase C (PKC) second messenger, inositol 1,4,5-trisphosphate (IP3), were assessed in two anurans, the freeze-tolerant wood frog, Rana sylvatica, and the freeze-intolerant leopard frog, Rana pipiens. Dehydration of wood frogs resulted in a rapid elevation of liver cAMP and PKAc; cAMP was 3.4-fold greater than control values in animals that had lost 5% of total body water, whereas PKAc was elevated threefold in 20% dehydrated frogs. These results indicate protein kinase A mediation of the liver glycogenolysis and hyperglycemia that is induced by dehydration in this species. Skeletal muscle PKAc content also rose with dehydration but neither cAMP nor PKAc was affected by dehydration in leopard frog tissues. Anoxia exposure had different effects on signal transduction systems. PKAc was elevated after 1 h anoxia in R. sylvatica brain and was sustained over time but the enzyme was unaffected in other organs; by contrast, R. pipiens showed variable responses by PKAc to anoxia in three organs. Both species showed rapid (within 30 min) and large (3 to 7.8-fold) increases in IP3 in liver of anoxic frogs that decreased slowly with continued anoxia. IP3 also increased quickly in heart of anoxia-exposed wood frogs. This suggests that PKC may mediate various metabolic adjustments that promote hypoxia/anoxia resistance such as coordinating metabolic rate depression. A progressive rise in liver IP3 during dehydration in wood frogs (reaching fourfold higher than controls in 40% dehydrated animals) may also mediate similar hypoxia resistance adaptations under this stress since anurans experience progressive hypoxia due to increased blood viscosity when water loss reaches high values. The patterns of second messenger and PKAc changes in wood frog liver during dehydration closely parallel the changes seen in these same parameters during natural freezing suggesting that the freeze tolerance of selected terrestrially hibernating anurans may have evolved out of various anuran mechanisms of dehydration resistance.

Animals↗

PubMed2006

Individual variation in alkaloid content of poison frogs of Madagascar (Mantella; Mantellidae).

Brightly colored Malagasy poison frogs, Mantella spp., sequester lipophilic, basic alkaloids from arthropod prey for their own chemical defense. Consequently, microsympatric prey diversity is expected to influence alkaloid diversity observed in poison frogs. Twenty-two specimens of three Mantella species from four localities in moist forests of southeastern Madagascar were analyzed individually via gas chromatography-mass spectrometry, revealing that they contain over 80 known alkaloids. Frogs within a locality possessed significantly similar alkaloid content and diversity, while frogs from areas that varied in disturbance, elevation, and/or species showed greater differences. Based on dietary data, the larger frog species Mantella baroni consumed more and larger prey, and showed greater diversity in skin alkaloids than significantly smaller Mantella bernhardi. Additionally, frogs from the most pristine locality had the greatest number of alkaloids, whereas individuals from the most disturbed localities had the least. In a comparison of frog alkaloid profiles over a 10- to 14-yr period, alkaloid turnover, and thus presumably alkaloid-source arthropod turnover, was high in a disturbed locality and low in the pristine primary forest locality. We demonstrate that the nonlethal transcutaneous amphibian stimulator (TAS) is effective for harvesting alkaloids from poison frogs; future studies using this device could obtain larger sample sizes without harming local frog populations.

Alkaloids↗

PubMed1997

Light-induced changes in frog pineal gland N-acetyltransferase activity.

N-Acetyltransferase (NAT) activity was determined in the pineal gland of frogs (Rana tigrina) of different ages using 2-aminofluorene and p-aminobenzoic acid as substrates, and assayed by high-pressure liquid chromatography. Frogs of different ages were either killed during the light phase or exposed to darkness or light for 1 min during the dark phase of the lighting cycle, then returned to their cages in darkness for 30 min before being killed. The pineal gland NAT activity of 1-month-old frogs was inhibited when the animal was nocturnally exposed to 1 min of light. Nocturnal light exposure did not inhibit NAT activity in 1-month-old frogs, even though these animal displayed clear light-dark differences in pineal gland NAT activity. Nocturnal light exposure did not inhibit night-time levels of NAT activity in 1-month-old animals which had been bilaterally enucleated, thus suggesting that this effect is retinally mediated. Pretreatment of 1-month-old and 6-month-old animals with isoproterenol (a beta-adrenoceptor agonist drug) prevented the nocturnal light-induced inhibition of NAT activity. From the different sensitivity of 1-month-old and 6-month-old animals to different intensities or durations of nocturnal light exposure it was found that the duration or intensity of light exposure was not able to inhibit nocturnal NAT activity. The NAT activity was at least 4-5-fold greater in 1-month-old frogs than in 6-month-old frogs. This is the first demonstration of the retino-pineal gland pathway that appears to produce light-induced changes in pineal glands of frogs 1-month-old or older, but this pathway only functions in 1-month-old frogs, and does not appear to function in 6-month-old frogs.

Aging↗

PubMed2000

Peptides with antimicrobial activity from four different families isolated from the skins of the North American frogs Rana luteiventris, Rana berlandieri and Rana pipiens.

The skins of frogs of the genus Rana synthesize a complex array of antimicrobial peptides that may be grouped into eight families on the basis of structural similarity. A total of 24 peptides with differential growth-inhibitory activity towards the Gram-positive bacterium Staphylococcus aureus, the Gram-negative bacterium Escherichia coli and the yeast Candida albicans were isolated from extracts of the skins of three closely related North American frogs, Rana luteiventris (spotted frog), Rana berlandieri (Rio Grande leopard frog) and Rana pipiens (Northern leopard frog). Structural characterization of the antimicrobial peptides demonstrated that they belonged to four of the known families: the brevinin-1 family, first identified in skin of the Asian frog Rana porosa brevipoda; the esculentin-2 family, first identified in the European frog Rana esculenta; the ranatuerin-2 family, first identified in the North American bullfrog Rana catesbeiana; and the temporin family, first identified in the European frog Rana temporaria. Peptides belonging to the brevinin-2, ranalexin, esculentin-1 and ranatuerin-1 families were not identified in the extracts. Despite the close phylogenetic relationship between the various species of Ranid frogs, the distribution and amino-acid sequences of the antimicrobial peptides produced by each species are highly variable and species-specific, suggesting that they may be valuable in taxonomic classification and molecular phylogenetic analysis.

Amino Acid Sequence↗

PubMedDate not supplied

Cricket frogs maintain body hydration and temperature near levels allowing maximum jump performance.

One goal of this study was to determine the combination of hydration and temperature in the northern cricket frog Acris crepitans that allowed maximum jump distance in the laboratory. Second, environmental variables in the field were measured to determine the best predictor(s) of mean body temperature and hydration and to determine whether frogs maintain levels of temperature and hydration yielding maximum jump distance. Laboratory data revealed that hydration and the hydration-temperature interaction significantly affected jump performance. Frogs at 95% and 85% hydration jumped significantly better than frogs at 75% hydration, but frogs at 95% hydration at 15 degrees C jumped significantly poorer than those at 95% hydration at 30 degrees C. Animals at 85% hydration at 30 degrees C and 85% hydration at 15 degrees C jumped just as well as those at 95% hydration at 30 degrees C. Mean body temperature of 55 frogs in the field was 28.0 degrees C, and hydration was 97.4%. Sky condition (sunny, cloudy, or partly cloudy) was the best predictor of frog hydration, and air temperature was the best predictor of frog body temperature. Cricket frogs in the field maintain a hydration and temperature near those found to yield maximum jump distances in laboratory trials. This may be a behavioral adaptation to allow maximum jump distance during predator avoidance.

Analysis of Variance↗

PubMedDate not supplied

Effects of frog-skin angiotensin II in amphibians.

The role of frog-skin angiotensin II (AII) in amphibia was studied by comparing the sodium and water permeability effects of three angiotensins (AII): frog skin (Ala-Pro-Gly-[Ile3, Val5]-Ang II), human [( Asp1, Ile5]-AII), and Japanese goosefish [( Asn1-Val5]-AII). Frog-skin AII increased the short-circuit current (SCC) significantly after it was added to the dermal side of the isolated skin of the South American frogs, Leptodactylus chaquensis and ocellatus, and the toad, Bufo arenarum, in concentrations of 10(-6) M. In frogs, the effect was significant at 15 minutes and reached 45% over control after 2 1/2 hours. The effect cannot be achieved with concentrations lower than 10(-7) M. Since amiloride (10(-4) M) blocked the SCC response, and absence of chloride in the bathing fluid did not, the effect is probably dependent on sodium transport. Human AII (10(-6) M) produced a similar response in summer frogs that had been treated with 0.1% NaCl for 14 days. Goosefish AII was ineffective at similar concentrations, and none of the angiotensins modified SCC in the toad bladder. Hydrosmotic effects could be achieved with the three angiotensins, the response being dependent on seasonal and species factors but always considerably lower than that of the neurohypophyseal peptides. Vascular reactivity of the isolated frog hindlimbs was compared by dose-response curves. Potency ratios on a molar basis against frog-skin AII was 1.136 for human AII and 1.193 for goosefish AII. The results show that the effects of the angiotensins differ in both the response of SCC to frog-skin angiotensin and its higher vascular effects.

Amphibians↗

PubMed2000

Immunohistochemical localization, biochemical characterization, and biological activity of neurotensin in the frog adrenal gland.

The primary structure of neurotensin has been recently determined for the frog Rana ridibunda (Endocrinology 139: 4140-4146, 1998). In the present study, we have investigated the distribution and biochemical characterization of neurotensin-like immunoreactivity in the frog adrenal gland, using an antiserum directed against the conserved C-terminal region of the peptide. Neurotensin-like immunoreactivity was detected in two populations of nerve fibers: numerous varicose fibers coursing between adrenal cells, and a few processes located in the walls of blood vessels irrigating the gland. Reversed-phase HPLC analysis of frog adrenal gland extracts revealed the existence of a major peak of neurotensin-like immunoreactivity that exhibited the same retention time as synthetic frog neurotensin. The possible involvement of neurotensin in the regulation of steroid secretion was studied in vitro using perifused frog adrenal slices. For concentrations ranging from 10(-10) to 10(-5) M, synthetic frog neurotensin increased corticosterone and aldosterone production in a dose-dependent manner (EC50 = 1.2 x 10(-9) M and 5.8 x 10(-10) M, respectively). Repeated administration of neurotensin induced a reproducible stimulation of steroid output without any tachyphylaxis. Prolonged administration (3 h) of frog neurotensin caused a transient increase in corticosterone and aldosterone secretion followed by a decline of corticosteroid secretion. Neurotensin also produced a significant stimulation of corticosteroid secretion from dispersed frog adrenal cells. This study demonstrates that neurotensin is located in nerve processes innervating the adrenal gland of amphibians. The results also show that synthetic frog neurotensin exerts a direct stimulatory effect on corticosteroid output. Taken together, these data support the view that neurotensin, released by nerve fibers, may act as a local regulator of corticosteroid secretion.

Adrenal Glands↗

PubMed1978

Induction of cleavage in nucleated and enucleated frog eggs by injection of isolated sea-urchin mitotic apparatus.

Mitotic apparatus (MA) were isolated in glycerol-dimethylsulphoxide solution (MTME) from zygotes of sea urchins (Stronglyocentrotus purpuratus). Freshly isolated MA were stored in 1/10 strength MTME for varying periods of time and were then injected into unfertilized frog (Rana pipiens) eggs. These injections induced 40-60% of the recipient frog eggs to initiate cleavage, resulting in the formation of blastula cell clusters. The cleavage-inducing activity of MA stored in 1/10 MTME at room temperature decreased with time of storage in 1/10 strength MTME, and disappeared by about 6 h. There was no change in the ultrastructure of MA during storage. MA isolated and stored in MTME at room temperature had a constant level of cleavage-inducing activity during the first 48 h of storage, but this activity slowly declined upon further storage; almost no activity was left after 3 weeks. MA isolated in hexylene glycol (HG) and immediately transferred into MTME were compared with MA isolated in MTME; both MA had the same cleavage-inducing activity on the day of isolation, after which the MA isolated in HG quickly lost activity. On the other hand, MA isolated and stored in HG had little cleavage-inducing activity when tested 3 h following isolation. Cleavage-inducing agent (CIA) isolated from frog brains induced cleavage and blastula formation when injected into nucleated frog eggs, but had no such activity when injected into enucleated frog eggs. MA isolated in MTME induced cleavage and blastula formation in enucleated frog eggs as well as in nucleated frog eggs. Cytological examination revealed that blastula cells which developed from MA-injected enucleated eggs contained Feulgennegative nuclei, whereas cells which developed from CIA-injected nucleated eggs contained Feulgen-positive nuclei. These results suggest that sea-urchin nuclear materials participate in mitosis in frog eggs. Isolated MA which had been stored in MTME for 3 weeks and which exhibited little cleavage-inducing activity were injected together with frog brain CIA into either normal or enucleated eggs; normal recipient eggs cleaved with significantly higher frequencies (70%) than those injected with CIA alone (40%). Furthermore, enucleated eggs injected with CIA alone failed to cleave, while those injected with MA and CIA together cleaved with significant frequencies (overall 29%). This result suggests a cooperative interaction between CIA and the inactivated MA to restore the cleavage-inducing activity of MA.

Animals↗

PubMed2006

Tribute to R. G. Boutilier: the role for skeletal muscle in the hypoxia-induced hypometabolic responses of submerged frogs.

Much of Bob Boutilier's research characterised the subcellular, organ-level and in vivo behavioural responses of frogs to environmental hypoxia. His entirely integrative approach helped to reveal the diversity of tissue-level responses to O(2) lack and to advance our understanding of the ecological relevance of hypoxia tolerance in frogs. Work from Bob's lab mainly focused on the role for skeletal muscle in the hypoxic energetics of overwintering frogs. Muscle energy demand affects whole-body metabolism, not only because of its capacity for rapid increases in ATP usage, but also because hypometabolism of the large skeletal muscle mass in inactive animals impacts so greatly on in vivo energetics. The oxyconformance and typical hypoxia-tolerance characteristics (e.g. suppressed heat flux and preserved membrane ion gradients during O(2) lack) of skeletal muscle in vitro suggest that muscle hypoperfusion in vivo is possibly a key mechanism for (i) downregulating muscle and whole-body metabolic rates and (ii) redistributing O(2) supply to hypoxia-sensitive tissues. The gradual onset of a low-level aerobic metabolic state in the muscle of hypoxic, cold-submerged frogs is indeed important for slowing depletion of on-board fuels and extending overwintering survival time. However, it has long been known that overwintering frogs cannot survive anoxia or even severe hypoxia. Recent work shows that they remain sensitive to ambient O(2) and that they emerge rapidly from quiescence in order to actively avoid environmental hypoxia. Hence, overwintering frogs experience periods of hypometabolic quiescence interspersed with episodes of costly hypoxia avoidance behaviour and exercise recovery. In keeping with this flexible physiology and behaviour, muscle mechanical properties in frogs do not deteriorate during periods of overwintering quiescence. On-going studies inspired by Bob Boutilier's integrative mindset continue to illuminate the cost-benefit(s) of intermittent locomotion in overwintering frogs, the constraints on muscle function during hypoxia, the mechanisms of tissue-level hypometabolism, and the details of possible muscle atrophy resistance in quiescent frogs.

Adenosine Triphosphate↗

PubMed1975

[Prevalence of sparganum of frogs (Rana nigromaculata) in Dae-jeon area, Chung-nam, Korea]

Prevalence of sparganum in the frog (Rana nigromaculata) was surveyed in Dae-jeon city and in suburbs of the city, Chungnam Do. 39 (3.9 %) out of 1,011 frogs were infected with the worm, and the highest prevalence rate of sparganum was found the frogs from Shintanjin area(11.3 %). Infection rates of sparganum were observed due to the body weight and sex of frogs. The highest infection rate of frogs, the body weight of 50 gms or more, showed 30.3 per cent(female: 41.7 %, male: none), on the other hand, no worm was found in young frogs(less than 10 gms). Distribution of sparganum in the frogs was recorded and 82.6 % of worms were distributed in the femoral intermuscular connective tissues of the hind legs. Among those infected frogs, number of worm burden was one to five worms, and 53.3 per cent of frogs were infected by only one worm.

Journal Article↗

PubMed1997

Localization of the FA-CHIP water channel in frog urinary bladder.

Like mammalian kidney collecting duct, the water permeability of frog urinary bladder epithelial cells is antidiuretic hormone (ADH)-sensitive. In kidney, this permeability is mediated by water channels named aquaporins. We recently reported the cloning of the frog aquaporin CHIP (FA-CHIP), a water channel from frog urinary bladder. FA-CHIP has 79% identity with rat Aquaporin 1 (AQP1) and only 42% identity with the kidney collecting duct Aquaporin 2 (AQP2). The purpose of this study was to examine the localization of FA-CHIP in frog urinary bladder. We raised antibodies against peptides of 15 to 17 residues, encompassing the N-ter and C-ter regions of FA-CHIP. Anti-FA-CHIP antibodies were used for Western blotting, indirect immunofluorescence microscopy and gold labeling electron microscopy in urinary bladder and other frog tissues. By Western blotting of frog urinary bladder total homogenate, the antibodies recognized a band of 29 kDa and glycosylated forms of the protein between 40 and 70 kDa. No signal was found on membrane preparations from epithelial cell homogenate. FA-CHIP was also found in frog skin, brain, gall bladder, and lung. In immunofluorescence microscopy on urinary bladder sections, FA-CHIP was localized to endothelial cells of blood capillaries and on mesothelial cells of the serosal face. Red blood cells, epithelial and basal cells were unstained. The localization of FA-CHIP in cell plasma membranes was confirmed by gold labeling electron microscopy. In other positive tissues, FA-CHIP was also localized to capillaries. In brain, plasma membranes of epithelial cells were also stained. In conclusion, like its mammalian homologue AQP1, FA-CHIP appears to be localized to constitutively water permeable cells of frog. Therefore, it belongs to the AQP1 family of proteins although unlike AQP1, FA-CHIP is absent from red blood cells and kidney. In frog urinary bladder and skin, FA-CHIP probably plays an important role in water transport across the barriers in series with the ADH-sensitive epithelial cells.

Animals↗

PubMed1997

Cutaneous transport of Ca2+ in the frog Rana pipiens: significance and specificity.

Rana pipiens were divided into four groups: controls; hypocalcemic frogs, depleted of salts by acclimation to deionized water; hypercalcemic frogs, calcium-loaded by the introduction of 40 mumol calcium gluconate; and frogs exposed to the potential competing ions Mg2+, Sr2+, and Ba2+. All groups displayed calcium influx that was proportional to external [Ca2+]; however, the group acclimated to deionized water also displayed hypocalcemia (P < 0.025) and enhanced Ca2+ influx at higher (> 0.3 mM) external [Ca2+]. Ca2+ efflux was depressed in hypocalcemic frogs, and thus net Ca2+ flux shifted from net loss in control frogs to net uptake in hypocalcemic frogs. Hypocalcemia also resulted in increased skin Ca2+ deposits which may be related to a decreased Ca2+ (and other ions) permeability as a consequence of the acclimation to deionized water. Another group of frogs was Ca(2+)-loaded by injecting calcium gluconate: Sodium gluconate controls did not significantly alter Ca2+ fluxes. The frogs that received calcium gluconate treatments became hypercalcemic (P < 0.01) and did not display significant changes in calcium fluxes, nor did they show significant changes in skin calcium deposits. We conclude that hypocalcemia leads to regulatory responses that stimulate active Ca2+ transport in Rana pipiens skin and possibly inhibits cutaneous and renal efflux. We also conclude that hypercalcemia does not alter calcium fluxes across skin. The ions from Group IIA of the Periodic Table of Elements had little effect on Ca2+ fluxes at concentrations ranging from 0.5-4.0 mM; neither Sr2+ or Ba2+ affected Ca2+ influx. The only divalent ion tested that influenced Ca2+ was Mg2+, which significantly inhibited Ca2+ influx but only at 4.0 mM or eight times the external [Ca2+]. We conclude, therefore, that the Ca2+ transport mechanism is fairly specific for Ca2+ within Group IIA.

Animals↗

PubMed1999

Inoculative freezing by environmental ice nuclei in the freeze-tolerant wood frog, Rana sylvatica.

Efficacy of inoculative freezing by ice nuclei in a simulated winter environment was studied in the wood frog (Rana sylvatica), a freeze-tolerant species that overwinters on the forest floor beneath organic detritus. Adult frogs were confined to plastic canisters and cooled to -2 degrees C over 24 hr with their ventral skin in contact with substrate (humic soil hydrated to 40, 10, or 5%, or soil/peat mixture hydrated to 20 or 10%, w/w), or their dorsal skin in contact with damp leaf mould. Whereas only 20% of control frogs cooled in dry, plastic canisters froze, freezing occurred in nearly all (98%) frogs contacting soil or leaf mould. Inoculation was briefly delayed in frogs exposed to drier substrates. Frogs exposed to an unfreezable substrate (humic soil, 5% moisture) themselves froze, apparently due to the action of constituent nuclei which commonly occur in natural materials. Although the surface over which inoculation can occur is greater in larger frogs, inoculation susceptibility was not correlated with body mass in our frogs (mean +/- SE body mass = 14.0 +/- 0.2 g; range, 9.8-17.8 g). We conclude that the high susceptibility to inoculative freezing in R. sylvatica, which is conferred by its moist, highly permeable integument, promotes freeze tolerance by ensuring that inoculation commences at relatively high temperatures.

Animals↗