An imidazole alphastat hypothesis for vertebrate acid-base regulation: Tissue carbon dioxide content and body temperature in bullfrogs

Reeves, Raymond

doi:10.1016/0034-5687(72)90030-8

Cited by 370 publications

(125 citation statements)

References 7 publications

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“…However, this time the fish was placed in a horizontal MR scanner at a magnetic field strength of 7 T. These experiments investigated the combined effects of temperature (acclimation as well as rapid change) and hypoxia on fish energy metabolism over several hours with a temporal resolution of minutes. These in vivo 31 P-NMR observations confirmed a negative correlation between temperature and intracellular pH in fish muscle in accordance with the alphastat pH regulation hypothesis developed by Reeves (1972). However, these experiments again involved the shortcomings of pre-experimental anaesthesia and fixation of the animal.…”

Section: Methodological Developmentssupporting

confidence: 85%

Oxygen limited thermal tolerance in fish?

Pörtner

Mark

Bock

2004

Respiratory Physiology & Neurobiology

108

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In various phyla of marine invertebrates limited capacities of both ventilatory and circulatory performance were found to set the borders of the thermal tolerance window with limitations in aerobic scope and onset of hypoxia as a first line of sensitivity to both cold and warm temperature extremes. The hypothesis of oxygen limited thermal tolerance has recently been investigated in fish using a combination of non-invasive nuclear magnetic resonance (NMR) methodology with invasive techniques. In contrast to observations in marine invertebrates arterial oxygen tensions in fish were independent of temperature, while venous oxygen tensions displayed a thermal optimum. As the fish heart relies on venous oxygen supply, limited cardio-circulatory capacity is concluded to set the first level of thermal intolerance in fish. Nonetheless, maximized ventilatory capacity is seen to support circulation in maintaining the width of thermal tolerance windows. The interdependent setting of low and high tolerance limits is interpreted to result from trade-offs between optimized tissue functional capacity and baseline oxygen demand and energy turnover co-determined by the adjustment of mitochondrial densities and functional properties to a species-specific temperature range. At temperature extremes, systemic hypoxia will elicit metabolic depression, thereby widening the thermal window transiently sustained especially in those species preadapted to hypoxic environments.

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Section: Methodological Developmentssupporting

confidence: 85%

Oxygen limited thermal tolerance in fish?

Pörtner

Mark

Bock

2004

Respiratory Physiology & Neurobiology

108

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“…Maintenance of the dissociation state (a) of histidine residues within proteins, especially in activity sites of enzymes, is seen as a key factor in this process (a-stat hypothesis). A pH change of around À0.018 pH units/ C is interpreted to maintain protein function when body temperature changes in ectothermic animals (a-stat pattern; Reeves, 1972). Even though literature is not uniform concerning the validity of the a-stat hypothesis recently the work of Ultsch and Jackson, 1996 and our own work (P .…”

Section: Introductionmentioning

confidence: 84%

Temperature-dependent pH regulation in eurythermal and stenothermal marine fish: an interspecies comparison using 31P-NMR

Sartoris

Bock

Pörtner

2003

Journal of Thermal Biology

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Temperature-induced pH changes in white muscle tissue of three eelpout populations with different levels of eurythermy (the cold stenothermal Antarctic species Pachycara brachycephalum and the temperate eelpout Zoarces viviparus from the North Sea and the Baltic Sea) were monitored online by use of in vivo 31 P-NMR in unrestrained, unanaesthetized fish. An intracellular pH (pH i ) change of around À0.015 pH units/ C was observed in all eelpout populations in accordance with the a-stat hypothesis. The pH change was completed earlier (within 4 h) in the stenothermal Antarctic eelpout than in the Baltic population (within 8 h) and latest (not within 12 h) in the eurythermal North Sea population. These findings confirm the hypothesis that the kinetics of temperature-dependent pH i regulation is reflected by the relative contribution of active and passive processes to a temperature-induced pH change. The extent of passively induced pH i changes is in line with the general hypothesis that the temperature-dependent adjustment of pH i occurs mostly by active mechanisms in eurythermal animals, whereas in stenothermal animals pH changes are largely elicited by passive processes. Temperature changes had no influence on high-energy phosphates like phosphocreatine and ATP or on the Gibbs free energy change of ATP hydrolysis (DG=Dx).

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“…The reason for the resistance to heat-induced pH-changes may lie in a temperature-induced change of the pK-value of histidine residues. This pK change compensates for the temperatureinduced acidification of the blood of poikolothermic invertebrates and guarantees a constant degree of histidine protonation [21]. This prevents acid-induced denaturation of the corresponding proteins.…”

mentioning

confidence: 97%

Extreme thermostability of tarantula hemocyanin

et al. 1995

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Biotops with extreme temperatures such as deserts force animals to avoid or escape high temperatures by biochemical, behavioural or morphological adaptation. In this context we tested the resistance to heat of the oxygen carrier hemocyanin from the ancient tarantula Eurypelma californicum, which is found in arid zones of North America. Differential scanning calorimetry, light scattering, crossed immunogelelectrophoresis and oxygen binding experiments show that the 24-meric hemocyanin is conformationally stable and fully functioning at temperatures up to 90°C. Our results demonstrate that the cation-mediated state of oligomerization is not only crucial for the high cooperativity of oxygen binding of this hemocyanin, but also for its extreme stability in the physiological temperature and pH range.

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An imidazole alphastat hypothesis for vertebrate acid-base regulation: Tissue carbon dioxide content and body temperature in bullfrogs

Cited by 370 publications

References 7 publications

Oxygen limited thermal tolerance in fish?

Oxygen limited thermal tolerance in fish?

Temperature-dependent pH regulation in eurythermal and stenothermal marine fish: an interspecies comparison using 31P-NMR

Extreme thermostability of tarantula hemocyanin

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