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PubMed2003

The effects of variation in climatic temperature (1980-2001) on breeding activity and tadpole stage duration in the common toad, Bufo bufo.

The effects of variation in climatic temperature on breeding behaviour and tadpole growth were investigated using data collected during a 22-year study of a single population of common toads, Bufo bufo, in southern England. Although the start of the breeding season each year, taken as the day when adult toads first arrived at their breeding pond in large numbers, showed no trend over time (1980-2001) it was highly correlated with climatic temperature. Thus, toads started breeding approximately 50 days earlier in the year following very mild winters (1993: February 2nd) compared with very cold ones (1986: March 23rd). Regression analysis of the relationship between the mean temperature of the 40 days immediately preceding the main arrival of toads at the breeding pond revealed that for every 1 degrees increase (or decrease) the toads arrived 12 days earlier (or later). Although the duration of the tadpole stage was longer when spawning was early, toadlets still emerged from the pond earlier than when spawning was late. The increased length of the tadpole stage, in years when spawning was early, was due to an increase in the proportion of cold days when the minimum ground temperature was at or below 0 degrees C. Thus, the tadpole stage was approximately 6 days longer (or shorter) for every 5% increase (or decrease) in the proportion of cold days the tadpoles were exposed to.

Animals↗
PubMed1996

The effect of galanin and galanin fragments on blood pressure in the Cane toad, Bufo marinus.

Galanin has previously been shown to have a slight vasodepressor or no effect on blood pressure in placental mammals, but causes potent increases in blood pressure in several other vertebrate species. In this paper, the part of the galanin molecule responsible for the pressor activity was investigated in the Cane road, Bufo marinus by administration of fragments of galanin into anaesthetised toads and isolated arterial segments in an organ bath. In anaesthetised toads, the order of efficacy was human galanin > porcine galanin > Gal 1-16 > Gal 1-15 > Gal 3-15 > Gal 21-29 = 0. In isolated vessels, the first three peptides were equally effective. When four fragments of human galanin were tested in anaesthetised toads, the order of efficacy was human galanin > Gal 1-15 > Gal 5-20 > Gal 10-25 > Gal 15-30. The substitution of alanine for tryptophan at position 2 or for tyrosine at position 9 abolished the pressor response to the human galanin fragment 1-18 in anaesthetised toads. These results suggest that vascular activity in the toad is retained within the N-terminus and that positions 2 (tryptophan) and 9 (tyrosine) are key amino acids in retention of the vascular activity of galanin.

Amino Acid Sequence↗
PubMed1997

Ouabain-sensitive Na+,K(+)-ATPase activity in toad brain.

Toads of the genus Bufo are highly resistant to the toxic effects of digitalis glycosides, and the Na+,K(+)-ATPase of all toad tissues studied to date has been relatively insensitive to inhibition by digitalis and related compounds. In studies of brain microsomal preparations from two toad species, Bufo marinus and Bufo viridis, inhibition of ATPase activity and displacement of [3H]ouabain from Na+,K(+)-ATPase occurred over broad ranges of ouabain or bufalin concentrations, consistent with the possibility that more than one Na+,K(+)-ATPase isoform may be present in toad brain. The data could be fitted to one- or two-site models, both of which were consistent with the presence of Na+,K(+)-ATPase activity with high sensitivity to ouabain and bufalin. Ki (concentration capable of producing 50% inhibition of activity) values for ouabain in the one-site model were in the 0.2 to 3.7 microM range, whereas Ki1 values in the two-site model ranged from 0.085 to 0.85 microM, indicating that brain ATPase was at least three orders of magnitude more sensitive to ouabain than B. marinus bladder ATPase (Ki = 5940 microM). Ouabain was also an effective inhibitor of 86Rb+ uptake in B. marinus brain tissue slices (Ki = 3.1 microM in the one-site model; Ki1 = 0.03 microM in the two-site model). However, the relative contribution of the high ouabain-sensitivity site to the total activity was 17% in the transport assay as compared with 63% in the Na+,K(+)-ATPase enzymatic assay. We conclude that a highly ouabain-sensitive Na+,K(+)-ATPase activity is present and functional in toad brain but that its function may be partially inhibited in vivo.

Animals↗
PubMed2001

Feeding causes thermophily in the woodhouse's toad (Bufo woodhousii).

(1) We placed 12 toads (Bufo woodhousii) in linear thermal gradients with floor temperatures ranging from 10 to 40 degrees C and monitored body temperatures (T(b)'s) with chromega-alomega thermocouples interfaced with a datalogger. (2) We measured T(b)'s at 10min intervals over a 24h period in toads that had eaten an equivalent of 5% of their body mass or had fasted for 5 days. (3) The mean 24h T(b) did not differ significantly between the fed and fasted groups. (4) Hourly mean T(b)'s of fed toads differed significantly over the 24h, but those of fasted toads did not. Fed toads selected highest T(b)'s during late afternoon and evening.

Journal Article↗
PubMed2002

Amino acid sequence of the major form of toad liver glutathione transferase.

To investigate structural relationship between amphibian and mammalian GSTs the complete amino acid sequence of the major form of glutathione transferase present in toad liver (Bufo bufo) was determined. The enzyme subunit is composed of 210 amino acid residues corresponding to a molecular mass of 24,178 Da. In comparison with the primary structure of amphibian bbGSTP1-1, toad liver GST showed 54% sequence identity. On the other hand, toad liver GST showed about 45-55% sequence identity when compared with other pi class GST and less then 25% identity with GST of other classes. Amino acid residues involved in the H site and in the key and lock structure of the toad enzyme are significantly different from those of bbGSTP1-1 and other mammalian pi class GST. On the basis of its structural and immunological properties the toad liver GST, indicated as bbGSTP2-2, could represent the prototype of a subset of the pi family.

Amino Acid Sequence↗
PubMed2003

Structural and biochemical characterization of toad liver fatty acid-binding protein.

Two paralogous groups of fatty acid-binding proteins (FABPs) have been described in vertebrate liver: liver FABP (L-FABP) type, extensively characterized in mammals, and liver basic FABP (Lb-FABP) found in fish, amphibians, reptiles, and birds. We describe here the toad Lb-FABP complete amino acid sequence, its X-ray structure to 2.5 A resolution, ligand-binding properties, and mechanism of fatty acid transfer to phospholipid membranes. Alignment of the amino acid sequence of toad Lb-FABP with known L-FABPs and Lb-FABPs shows that it is more closely related to the other Lb-FABPs. Toad Lb-FABP conserves the 12 characteristic residues present in all Lb-FABPs and absent in L-FABPs and presents the canonical fold characteristic of all the members of this protein family. Eight out of the 12 conserved residues point to the lipid-binding cavity of the molecule. In contrast, most of the 25 L-FABP conserved residues are in clusters on the surface of the molecule. The helix-turn-helix motif shows both a negative and positive electrostatic potential surface as in rat L-FABP, and in contrast with the other FABP types. The mechanism of anthroyloxy-labeled fatty acids transfer from Lb-FABP to phospholipid membranes occurs by a diffusion-mediated process, as previously shown for L-FABP, but the rate of transfer is 1 order of magnitude faster. Toad Lb-FABP can bind two cis-parinaric acid molecules but only one trans-parinaric acid molecule while L-FABP binds two molecules of both parinaric acid isomers. Although toad Lb-FABP shares with L-FABP a broad ligand-binding specificity, the relative affinity is different.

Amino Acid Sequence↗
PubMed1998

Microfluorometric analyses of glycogen in freshly dissected, single skeletal muscle fibres of the cane toad using a mechanically skinned fibre preparation.

The main objective of this study was to analyse glycogen in single muscle fibres, using a recently developed microfluorometric method which detects subpicomol amounts of NADPH, glucose and glycogen (as glucosyl units) (detection limit 0.16-0.17 pmol in a 25 nl sample) without fluorochrome amplification. The fibres were freshly dissected from the twitch region of the iliofibularis muscle of the cane toad (Bufo marinus), and were mechanically skinned under paraffin oil to gain access to the intracellular compartments. The results show that (1) glycogen concentrations in toad skeletal muscle fibres range between 25.8 and 369 mmol glucosyl units/litre fibre volume; (2) there is a large variation in glycogen content between individual fibres from the iliofibularis muscle of one animal; (3) there are seasonal differences in the glycogen content of toad single muscle fibres; (4) the total amount of glycogen in single muscle fibres of the toad does not decrease significantly when storing the tissue, under paraffin oil, at 20-25 degree C for up to 6 h or at 4 degree C for up to 24 h; and (5) 15-26% of fibre glycogen can be washed in an aqueous solution at pH 5-7, within 5 min, while 74-85% of fibre glycogen remains associated with the washed skinned fibre, even after 40 min exposure of the skinned fibre preparation to the aqueous environment. The retention of most glycogen in the fibre preparation after mechanical removal of the plasma membrane and extensive washing indicates that in toad skeletal muscle fibres the largest proportion of glycogen is tightly bound to intracellular structures. The results also show that the skinned muscle fibre preparation is well suited for microfluorometric glycogen determination, since low molecular weight non-glycogen contributors to the fluorescence signal can be removed from the myoplasmic space prior to the glycogen hydrolysis step.

Animals↗
PubMed2002

Myosin heavy chain isoform expression and Ca2 +-stimulated ATPase activity in single fibres of toad rectus abdominis muscle.

Segments of single fibres from the rectus abdominis (RA) muscles of adult and juvenile cane toads (Bufo marinus) were examined for myosin heavy chain (mHC) isoform expression and Ca2+-stimulated MgATPase activity. mHC isoform analyses were carried out using the recently developed alanine-SDS-PAGE method, which separates one tonic (BmHCT) and three twitch (BmHC1, BmHC2, BmHC3) mHC isoforms in toad skeletal muscle. Ca2+-stimulated MgATPase activity was measured by spectrophotometric determination of Pi, under conditions in which the ATPase associated with the sarcoplasmic reticulum (SR ATPase) was suppressed by feedback inhibition. The mHC-based fibre types identified in this study include three pure twitch fibre types (t1, t2 and t3), expressing BmHC1, BmHC2 or BmHC3 respectively, and seven hybrid fibre types co-expressing a combination of two or three twitch and tonic or twitch and twitch mHC isoforms. The fibre populations dissected from juvenile and adult toad muscles contained 49.4% (juvenile) and 73.7% (adult) mHC hybrids. The average values for Ca2+-stimulated MgATPase in pure twitch fibres and in fibres expressing predominantly (> or = 95%) the tonic mHC isoform (Tp fibres) differed significantly (P < 0.05) from each other and decreased in the order t1 > t2 > t3 > Tp. We conclude that (i) in RA muscles of both juvenile and adult cane toads there is a large proportion of mHC hybrids, some of which co-express twitch and tonic mHC isoforms and (ii) ATPase activities associated with the four mHC isoforms expressed in toad skeletal muscles decrease in the order BmHC1 > BmHC2 > BmHC3 > BmHCT.

Animals↗
PubMed2000

Bufokinin: actions and distribution in the toad cardiovascular system.

1. Bufokinin is a substance P-like neuropeptide and potent spasmogen isolated from the intestine of the cane toad Bufo marinus. In the present study, we investigated the effects of bufokinin on systemic blood pressure and heart rate in the anaesthetized toad and the distribution of bufokinin-like immunoreactivity in the toad vasculature. 2. Intravenous bufokinin caused a dose-dependent fall in systemic blood pressure (maximum fall 20 mmHg) with an ED50 of 2.9 pmol. At higher doses, the effect was prolonged and blood pressure did not return to baseline within 60 min. There was no significant change in heart rate associated with hypotension. 3. Bufokinin-like immunoreactivity was mapped in whole mounts of toad blood vessels and organs using a mouse polyclonal antibody BK3 (at 1:5000) and the avidin-biotin method. Bufokinin-immunoreactive fibres were associated with most blood vessels examined: a moderately dense perivascular network of varicose fibres was present around renal arteries, with sparser immunoreactive fibres in the ventral aorta, sciatic artery, anterior abdominal vein and hepatic portal vein. 4. Bufokinin-immunoreactive fibres, mainly following blood vessels, were seen in whole mounts of the urinary/bladder and tongue, but not in the air sac. In the heart ventricle, varicose fibres were found in the valve cusps, intracardiac ganglia, epicardium and myocardium close to the endocardium, but not in the rest of the myocardium. 5. The vasodepressor action of bufokinin and the presence of bufokinin-like immunoreactivity in varicose fibres in various vessels suggest a role for bufokinin in haemodynamic regulation and/or sensory nerve function in the toad. The lack of any reflex tachycardia in response to the falls in blood pressure was of note.

Animals↗
PubMed2003

Role of environmental pollutants on immune functions, parasitic infections and limb malformations in marine toads and whistling frogs from Bermuda.

Soil, water, and amphibian tissues collected between 1995 and 1999 from 15 study sites in Bermuda were analysed for pesticides and heavy metals. The most abundant pesticide residue in soil was p,p'-dichlorodiphenyldichloroethylene (DDE) which was found at all sites in concentrations ranging from 0.003 to 4.023 p.p.m. No pesticide residues were found in water. DDE was also recovered from the livers and fat bodies of marine toads (Bufo marinus) and whistling frogs (Eleutherodactylus johnstonei). Analyses of food sources consumed by these anuran species revealed residue levels of p, p'-DDE ranging from 0.05 to 0.217 p.p.m. Other soil residues included dichlorodiphenyltrichloroethane (DDT) at eight study sites, Dicofol(kelthane) at eight sites, dieldrin at five sites, and polychlorinated biphenyls (PCBs) as Arochlor 1254 and Arochlor 1260 at seven sites. Analyses of toad livers revealed significant concentrations of cadmium, chromium, copper and zinc. Livers of Bermuda toads exhibited altered hepatocytic morphology and an increased number of melanomacrophages and possible granulomas, while spleens showed a marked decrease in white pulp. Spleen cells from Bufo marinus collected at one site having high levels of cadmium exhibited a decreased B cell response to lipopolysaccharide. The incidence of trematode infection in Bufo marinus increased from 53.8% in 1995 to 90% in 1999. Deformity rates in the limbs of subadult and adult toads ranged between 15 and 25%. Examination of 1,995 newly-metamorphosed toads revealed deformity rates as high as 47%. The current comprehensive study suggests that environmental pollutants may account for immunosuppression, increased susceptibility to infections, limb malformations and possible decline in amphibian populations from Bermuda.

Animals↗
PubMed1958

Active sodium transport by the isolated toad bladder.

Studies were made of the active ion transport by the isolated urinary bladder of the European toad, Bufo bufo, and the large American toad, Bufo marinus. The urinary bladder of the toad is a thin membrane consisting of a single layer of mucosal cells supported on a small amount of connective tissue. The bladder exhibits a characteristic transmembrane potential with the serosal surface electrically positive to the mucosal surface. Active sodium transport was demonstrated by the isolated bladder under both aerobic and anaerobic conditions. Aerobically the mean net sodium flux across the bladder wall measured with radioactive isotopes, Na(24) and Na(22), just equalled the simultaneous short-circuit current in 42 periods each of 1 hour's duration. The electrical phenomenon exhibited by the isolated membrane was thus quantitatively accounted for solely by active transport of sodium. Anaerobically the mean net sodium flux was found to be slightly less than the short-circuit current in 21 periods of observation. The cause of this discrepancy is not known. The short-circuit current of the isolated toad bladder was regularly stimulated with pure oxytocin and vasopressin when applied to the serosal surface under aerobic and anaerobic conditions. Adrenaline failed to stimulate the short-circuit current of the toad bladder.

Animals↗
PubMedDate not supplied

Toad atrial natriuretic peptide: cDNA cloning and functional analysis in isolated perfused kidneys.

A complementary DNA (cDNA) encoding Bufo marinus (toad) preproatrial natriuretic peptide (preproANP) was isolated by reverse-transcription polymerase chain reaction. Sequence analysis of toad preproANP cDNA revealed an open reading frame of 150 amino acid residues, which shared 72% and 66% identity with Rana catesbeiana and Xenopus laevis preproANP, respectively. The deduced amino acid sequence of toad ANP that corresponded to ANP 1-24 of R. catesbeiana and Rana ridibunda was identical, but it differed by four residues from that of X. laevis. ANP mRNA transcripts were also shown to be expressed in the toad kidney. Subsequently, the effect of frog ANP (1-24) on renal function in toad was examined using a perfused kidney preparation. The arterial infusion of frog ANP caused a dose-dependent decrease in the arterial perfusion pressure that was associated with an increase in the glomerular filtration rate (GFR) and a renal natriuresis and diuresis. The renal natriuresis and diuresis resulted predominantly from an increased GFR rather than from direct tubular effects. This study demonstrates that ANP can regulate renal function, which suggests it may be involved in overall fluid volume regulation.

Amino Acid Sequence↗
PubMed1993

Digitalis-like compounds in the toad Bufo viridis: interactions with plasma proteins.

Digitalis-like compounds (DLC), normal constituents of animal tissues, are possible regulators of the Na+,K(+)-ATPase implicated in water and salt homeostasis. DLC are present in toad (Bufo viridis) tissues. Although DLC highest levels were found in toad skin, it was also detected in plasma and many internal organs. The abundant distribution and the different levels of DLC in various tissues exclude the possibility that toxicity is the only function of these compounds in the toad. The concentration of DLC in toad plasma is 30 microM, out of which 25-30% is bound to plasma proteins. Fractionation of toad plasma proteins on a G-100 Sephadex column followed by the extraction of DLC from the plasma proteins revealed that DLC are bound primarily to proteins of 48,000-53,000 Da. These results establish the existence of bufodienolide-binding protein(s) in animal plasma.

Animals↗
PubMed1975

Salt-induced changes in sodium transport across the skin of the euryhaline toad, Bufo viridis.

1. Euryhaline toads (Bufo viridis) were adapted to either distilled water, 115 or 200 mM-NaCl solutions. Na transport across the skin of these animals was studied in in vitro preparations. 2. Salinity adaptation caused a reduction in transepithelial potential and short-circuit current across the skin, and increased its electrical resistance. 3. Na influx across the skin was decreased. The reduction accounted fairly well for the measured reduction in short-circuit current. 4. Short-term Na uptake at the outer barrier of the skin was greatly reduced in preparations from salt adapted animals. Amiloride, which usually inhibits Na uptake, did not affect it in skins from salt adapted toads. 5. Sodium conductance decreased by a factor of three in skins from 115 mM-NaCl adapted toads, and to zero in skins from 200 mM-NaCl adapted animals. Shunt conductance was only little affected by the salinity of adaptation. 6. 'Amiloride-sensitive component' of transepithelial Na transport was 55, 21-5, and 4-5 muA/cm-2 in skins from toads which were adapted to distilled water, 115, and 200 mM-NaCl solutions, respectively. 7. It is concluded that the effect of salinity adaptation on the skin of the toad is to reduce the number of Na selective sites at the outer barrier. This change is reflected in a decrease in the 'amiloride-sensitive component' of Na transport across the skin, and could not be increased by aldosterone. Other changes may occur as secondary to that.

Adaptation, Physiological↗
PubMed1976

The passive permeability of the skin of anuran amphibia: a comparison of frogs (Rana pipiens) and toads (Bufo marinus).

1. Efflux of Na across dorsal skin, in vitro (bathed on both sides with Ringer solution), of frogs and toads were similar, but it was greater in ventral skin from the latter. 2. The efflux of Na declined, in both species, when the external surface of ventral, but not dorsal, skin was exposed to hyposmotic solutions with a low Na concentration. This change in Na permeability was influenced by the low osmotic concentration as well as the low Na concentration. 3. Efflux of Cl was similar in both the dorsal and ventral skin preparations (Ringer on both sides) from frogs and toads. 4. Chloride efflux declined in all skin preparations exposed on the external surface to dilute Ringer solution. Solute replacement with sucrose or choline or Na2SO4 showed that the decreased Cl efflux was principally due to the low Cl concentration, though Na may also contribute. This observation suggests the presence of Cl-/Cl- exchange diffusion mechanism. 5. Cutaneous urea permeability was less in toads than frogs and the dorsal and ventral skin was similar with respect to this solute in each species. 6. The presence of external hyposmotic solutions reduced the efflux, but not the influx, of urea across frog, but not toad, skin and it appeared that solvent 'drag' may contribute to this change. 7. Diffusion permeability to water was greater in frogs than toads and in the latter the ventral skin was more permeable than the dorsal. 8. The passive permeability of amphibian skin shows considerable interspecific and regional differences to various molecules which do not necessarily parallel each other. The control of passive cutaneous permeability appears to involve a variety of specific mechanisms, the distribution of which may have evolved during their adaptation to different environments.

Animals↗
PubMed1989

Dissociation of force from myofibrillar MgATPase and stiffness at short sarcomere lengths in rat and toad skeletal muscle.

1. Single fast-twitch fibres from the extensor digitorum longus muscle of the rat, Rattus norvegicus, and single twitch fibres from the iliofibularis muscle of the cane toad, Bufo marinus, were mechanically skinned and then used to measure maximally Ca2+-activated [( Ca2+] greater than 0.03 mmol l-1) isometric force production, myofibrillar MgATPase activity and fibre stiffness at different sarcomere lengths. MgATP hydrolysis was linked by an enzyme cascade to the oxidation of NADH (nicotinamide adenine dinucleotide, reduced form) and was monitored by a microfluorimetric system. Fibre stiffness was measured from the amplitude of force oscillations generated by small sinusoidal length changes. 2. At sarcomere lengths which were optimal for isometric force production (around 2.7 microns for rat and 2.2 microns for toad fibres) the myofibrillar MgATPase activity (mean +/- S.E.M.) at 21-22 degrees C was found to be 3.80 +/- 0.53 molecules MgATP hydrolysed s-1 per myosin head for eight rat fibres and 6.35 +/- 0.77 s-1 per myosin head for four toad fibres. 3. At sarcomere lengths shorter than 2.7 microns in rat fibres and 2.2 microns in toad fibres, MgATPase and stiffness remained elevated and close to their respective values at 2.7 microns in rat fibres and 2.2 microns in toad fibres even when the isometric force decreased to near zero levels. 4. The dissociation at short sarcomere lengths of myofibrillar MgATPase activity and fibre stiffness from isometric force suggests that the cross-bridge cycle is not greatly affected by double actin filament overlap with the myosin filaments at short sarcomere lengths. Moreover, the results suggest that cross-bridges can be formed by myosin with actin filaments projecting from the nearest Z-line and from the Z-line in the other half of the sarcomere. 5. These results help to reconcile energetic and mechanical data obtained by others at short sarcomere lengths and can be explained within the framework of the sliding filament theory.

Adenosine Triphosphate↗
PubMed1994

Effects of heparin on excitation-contraction coupling in skeletal muscle toad and rat.

1. Intracellularly applied heparin was found to cause a novel, use-dependent block of excitation-contraction (E-C) coupling in skinned skeletal muscle fibres of the toad. After one to four depolarizations in the presence of 100 micrograms ml-1 heparin, no further depolarization-induced responses could be elicited, even though addition of caffeine or lowering [Mg2+] could still induce massive Ca2+ release. This effect could not be reversed by extensive wash-out of the heparin (> 15 min). 2. Heparin (100 micrograms ml-1) did not abolish subsequent depolarization-induced responses if applied while the voltage sensors were in either their resting or inactivated states, that is (a) while a fibre remained fully polarized, (b) when a fibre was already chronically depolarized or (c) after a fibre had been depolarized in the presence of D600 (gallopamil) and then repolarized. 3. When a toad fibre was depolarized in heparin, with the associated Ca2+ release blocked by the presence of 10 mM intracellular Mg2+, subsequent E-C coupling was abolished. Heparin did not interrupt E-C coupling when Ca2+ release was triggered in the absence of any depolarization, by either caffeine or low [Mg2+]. Thus, the opening of the Ca2+ release channels was neither necessary nor sufficient for heparin to abolish E-C coupling. 4. Heparin had direct effects on the contractile apparatus in toad fibres, increasing the Ca2+ sensitivity and decreasing the maximum Ca(2+)-activated force. These effects could only be partly reversed by extensive wash-out of heparin. 5. At 100 micrograms ml-1, both low molecular weight heparin and pentosanpolysulphate, another highly sulphated polysaccharide, were less effective than heparin in blocking the depolarization-induced response and in changing the properties of the contractile apparatus, and these effects could be substantially reversed by wash-out. Two other polyanions, de-N-sulphated heparin (100 micrograms ml-1), which lacked N-sulphate groups, and polyglutamate (500 micrograms ml-1), had no measurable effect on either E-C coupling or the contractile apparatus. 6. In skinned fibres of the extensor digitorum longus muscle of the rat, 100 micrograms ml-1 heparin had little or no effect on E-C coupling and on the Ca2+ sensitivity of the contractile apparatus, but caused a larger reduction of the maximum Ca(2+)-activated force than in skinned fibres of the toad. 7. These results indicate that heparin blocks E-C coupling in toad muscle if, and only if, it is present when the voltage sensors are activated by depolarization.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2003

Toad venom poisoning: resemblance to digoxin toxicity and therapeutic implications.

A healthy man developed gastrointestinal symptoms after ingesting purported aphrodisiac pills. He had severe unrelenting bradycardia, hyperkalaemia, and acidosis. He rapidly developed severe life threatening cardiac arrhythmias and died after a few hours. He was found to have positive serum digoxin concentrations, although he was not taking digoxin. Toad venom poisoning is similar to digitalis toxicity and carries a high mortality. Cardiac glycoside poisoning can occur from ingestion of various plants and animal toxins, and the venom gland of cane toad (Bufo marinus) contains large quantities of cardiac glycosides. Toad venom, a constituent of an aphrodisiac, was considered responsible for the development of clinical manifestations and death in this patient. Digoxin specific Fab fragment has been reported to be beneficial in the treatment of toad venom poisoning. This report alerts physicians to the need to be aware of a new community toxic exposure, as prompt treatment with digoxin specific Fab fragment may be life saving. The treatment approach to patients with suspected toad venom poisoning is described.

Adult↗