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  • 1
    Electronic Resource
    Electronic Resource
    Exchanges of oxygen, carbon dioxide, nitrogen and water in the caecilian Dermophis mexicanus (2000)
    Springer
    Journal of comparative physiology 170 (2000), S. 505-509 
    Details
    ISSN: 1432-136X
    Keywords: Key words Ammonotelism ; Ureotelism ; Osmotic flux ; Arginine vasotocin ; Mesotocin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Oxygen consumption was measured in five Dermophis mexicanus and averaged (±SEM) 0.047 ± 0.004 ml O2 g−1 h−1. Carbon dioxide production averaged 0.053 ± 0.005 ml CO2 g−1 h−1 in the same five animals 1 week later. This metabolic rate is similar to metabolic rates of other Gymnophionans but lower than metabolic rates reported for Anurans and Urodeles. Total nitrogen excretion averaged 1.37 μmol N g−1 h−1 which is higher than that found for other amphibians. Of this, 82.5% (1.13 μmol N g−1 h−1) was in the form of urea while 17.5% (0.24 μmol N g−1 h−1) was in the form of NH3 + NH+ 4. Such ureotelism is typical of terrestrial amphibians like D. mexicanus. Osmotic water flux averaged 0.0193 ml g−1 h−1 in control (sham injected) animals and was not significantly altered by injection of either arginine vasotocin or mesotocin. This osmotic flux is similar to osmotic fluxes found for other terrestrial amphibians. The combined data suggest that metabolism in D. mexicanus is, like most other Gymnophionans, lower than other amphibians. The high rates of nitrogen (especially urea) excretion suggests that this fossorial animal accumulates urea like other burrowing amphibians.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003600000128
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  • 2
    Electronic Resource
    Electronic Resource
    Blood-gas, acid-base and catecholamine responses to lactic acid infusion in larval and adult Ambystoma tigrinum (1994)
    Springer
    Journal of comparative physiology 164 (1994), S. 355-361 
    Details
    ISSN: 1432-136X
    Keywords: pH-value ; Norepinephrine ; β1 ; β2 ; Amphibia ; Ambystoma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Larval and adult Ambystoma tigrinum were subjected to acidosis by infusing lactic acid (2 μM·g-1) into the peritoneal cavity. Blood was sampled at intervals to establish the time-course of the ensuing acidosis. Both larvae and adults became significantly acidotic after 1 h. The larval acidosis was more pronounced (-4 pH units versus-2 pH units) than adults due to greater extracellular buffering capacity (higher [HCO3 -]) in adults. Both forms recovered in about 8 h. Larvae showed a typical increase in circulating norepinephrine during the initial stages of the acidosis; adults did not, having significantly lower norepinephrine titer than larvae during the acidosis. Both larvae and adults showed transient increases in PO2 during the acidosis. The β1 and β2 antagonists, timolol and butoxamine respectively, (0.2 μg·g-1) were administered to separate groups of larvae. Butoxamine (β2) delayed the recovery from the acidosis by prolonging the increase in arterial PCO2 and reversing the recovery of [HCO3 -]. Timolol (β1) did not delay recovery. We conclude that β2 receptors are involved in the catecholamine responses to acidosis in larvae. Catecholamines appear not to play the same role in adult acid-base disturbances as they seem to in larvae.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00302550
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  • 3
    Electronic Resource
    Electronic Resource
    Cardiovascular responses to metabolic and respiratory acidosis and anesthesia in larval Ambystoma tigrinum (1994)
    Springer
    Journal of comparative physiology 164 (1994), S. 272-277 
    Details
    ISSN: 1432-136X
    Keywords: Amphibia ; Circulation ; Skin ; Acid-base-balance ; Heart
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Larval Ambystoma tigrinum were examined to determine their cardiovascular responses to three types of acidosis: metabolic acidosis via NH4Cl gavage; respiratory acidosis via hypercapnia; and anesthetic-induced acidosis, via triacine methanesulphonate. In addition, another group of (metabolic acidosis) animals were tested to determine the role of β-mediated catecholamine control on cardiovascular and acid-base regulation. The metabolic and respiratory acidoses produced typical amphibian responses. Anesthesia produced a significant mixed acidosis with respiratory and metabolic components. The cardiovascular responses to metabolic and respiratory acidosis were increased heart rate and pulse pressure. There were no significant changes in diastolic pressure, however, systolic pressure increased as a result of the increased pulse pressure. Animals subjected to metabolic acidosis via β-blockade with propranolol did not display the increased heart rate and pulse pressure and the acidosis was deepened and prolonged. Anesthesia resulted in a cardiac slowing and increased pulse pressure, probably explained by the Frank-Starling relationship. There was no change in diastolic pressure. Anesthetized animals had depressed blood O2 tension and elevated blood lactate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00346442
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  • 4
    Electronic Resource
    Electronic Resource
    Active transport of Calcium ions in the skin of the salamander Ambystoma tigrinum (1999)
    Springer
    Journal of comparative physiology 169 (1999), S. 481-486 
    Details
    ISSN: 1432-136X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract We measured Ca2+ exchanges across the skin of larval and adult Ambystoma tigrinum using the radio-isotope influx method. We found that the skin of both morphs takes up Ca2+ in a manner that is proportional to external [Ca2+], saturable and oriented against the electrochemical gradient for Ca2+. We conclude that this uptake occurs by active transport. Kinetic analysis yields affinities for calcium ions that are similar to the affinities for both Ca2+ and Na+ in the skin of other amphibians. The capacity for calcium is similar to Ca2+ capacity in other amphibians. The capacity for Ca2+ is lower than the capacity for Na+. Cutaneous Ca2+ deposits are lower in this urodele than found in anurans. Adults tend to have higher levels of Ca in their skin than do larvae.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003600050245
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  • 5
    Electronic Resource
    Electronic Resource
    Active calcium ion transport in Xenopuslaevis skin (1997)
    Springer
    Journal of comparative physiology 167 (1997), S. 328-334 
    Details
    ISSN: 1432-136X
    Keywords: Key wordsApical calcium channels ; Nifedipine ; Diltiazem ; Verapamil ; L-channels ; Lanthanum ; Cobalt ; Nickel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The skin of intact, free-swimming Xenopus laevis transports Ca2+ inwardly in a manner that is proportional to the external [Ca2+] up to about 0.3 mmol · l−1, saturates above 0.3 mmol · l−1, and is opposed to the electrochemical gradient. Efflux is relatively constant at external concentrations between 0.016 and 0.6 mmol · l−1; net flux which is negative below 0.125 mmol · l−1 becomes positive above this external [Ca2+]. Allometric analysis suggests that both Ca2+ influx and efflux scale to the 2/3 power approximately like surface area. There were no significant differences in influx between summer and fall animals; however, efflux was greater in the fall and this resulted in a change from positive balance in the summer to negative balance in the fall. Isolated skins were shown to support a Ca2+ uptake rate of nearly 30 nmol · cm−2 · h−1. The phenylalkylamine verapamil in the apical bathing solution significantly inhibited this at 25 μmol · l−1. The benzothiazepine diltiazem was also effective at 50 μmol · l−1 while the dihydropyradine nifedipine was ineffective up to 100 μmol · l−1. The inorganic ion La3+ was effective at blocking Ca2+ uptake at 300 μmol · l−1; Ni2+ was also effective at 500 μmol · l−1 but Co2+ was ineffective up to 500 μmol · l−1. These results suggest that apical calcium channels in Xenopuslaevis skin have properties similar to mammalian L-channels and fish gill Ca2+ channels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003600050081
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