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Physiological adaptations for development among some intertidal muricid gastropods
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Abstracts / Comparative Biochemistry. and Physiology, Part B 126 (2000) S1-S108
EFFECT OF OXIDANTS ON POTASSIUM TRANSPORT IN RED BLOOD CELLS OF HERBIVORES IM. C. M u z y a m b a , 2p. F. S p e a k e & 3j. S. G i b s o n t Veterinary Preclinical Sciences, U n i v e r s i t y o f L i v e r p o o l ; 2Child Health, U n i v e r s i t y o f M a n c h e s t e r ; and 3physiology, St G e o r g e ' s H o s p i t a l M e d i c a l S c h o o l U n i v e r s i t y o f L o n d o n , L o n d o n , S W 1 7 ORE. Animals are exposed to oxidants from a variety of sources. Ingested nitrates, for example found at high levels in contaminated water, heavily fertilised herbiage or Brasssica spp., are converted to nitrites in the anaerobic conditions of the tureen or large intestine. Ialrogenic therapy with oxidant reagents may also occur inadvertently, such as administration of phenylhydrazine or vitamin K to horses and certain dogs. Exposure of red blood cells to oxidants has several important consequences. First, oxidation of haemoglobin to methaemoglohin (metHb) will decrease the oxygencarrying capacity of the cells, and can cause hypoxia of peripheral tissues. Second, oxidants also alter the behaviour of red blood cell membrane solute transporters, especially the inorganic ion co- and counter-transporters. The latter action is important because it will alter red blood cell ion balance and hence cell volume. It may also alter plasma ion concentrations, notably of K +. Thus it has been shown previously that oxidants stimulate the K+-C1" cotransporter (probably KCC1) in red blood cells from a number of different species, including human and sheep, but inhibit the Na+/IT exchanger (3-NHE) of trout (see Gibson et al., 2000, for references). The generation of metHb also activates KCCI in deoxygenated red blood cells of trout and carp, a transporter which is normally inactive at low oxygen tensions. The effect of oxidants on these membrane transporters will depend not only on the effects of oxidants per se, but also, critically, on their ability to respond to physiological stimuli which might further modulate transporter activity, notably O2 tension, cell volume, IT ions and urea. In this study, we used S6Rb+ as a K + congener to investigate the activity of KCCI in red blood cells from horses and cattle in response to the oxidants nitrite and 1-chloro-2,4-dinitrobenzene. We confirm that these oxidants stimulate the activity of KCCI. In addition, we investigated how the transporter was then able to respond to the other major physiological stimuli to which the cells would be exposed in vivo. The transporter was fully responsive to three of these stimuli (cell volume, IT ions and urea), but became progressively less O2-sensitive as the oxidant challenge increased. These findings may be relevant for understanding the pathology of oxidant toxicity and for development of rational chemotherapy to prevent its deleterious effects. This work is supported by The Wellcome Trust. MCM is a Beit Fellow and holder of an ORS award. Gibson, J. S. et al. (2000). J. exp. Biol. 203: 1395-1407.
PHYSIOLOGICAL ADAPTATIONS FOR DEVELOPMENT AMONG SOME INTERTIDAL MURICID G A S T R O P O D S M.S. N e w e l and G.B. Bourne D e p a r t m e n t o f Biological Sciences, U n i v e r s i t y o f Calgary, Calgary, Alberta, C a n a d a T 2 N 1N4 and the Barnfield Marine Station, Barn_field, British C o l u m b i a , C a n a d a V 0 R 1B0 The intertidal zone is a complex and heterogeneous habitat that exposes organisms to highly variable and often harsh environmental conditions. Intertidal gastropods display a wide range of morphological, physiological and behavioural adaptations for periodic emersion, which have been correlated with the tidal heights they inhabit. Similarly, egg capsules deposited in the intertidal zone are also subjected to the stresses associated with emersion. The variety of both the capsule morphology and the life history strategies employed by the muricid gastropods provides an opportunity to study the constraints of encapsulated development in the intertidal zone. Thus, we measured the effects of certain environmental parameters on the egg capsule morphology and several measurements of physiological performance of the capsules ofNucella ostrina and N. lamellosa in comparison to those of other muricid gastropods. An examination of the capsules deposited by the high intertidal Nucella ostrina and the lower intertidal N. lamellosa indicated that despite an extensive overlap in both the wet masses and chamber volumes there were two important differences. The capsules ofN. ostrina had significantly thicker walls and a lower surface area to volume ratio compared to those ofN. lamellosa. In contrast, the capsules of a closely related muricid gastropod Ceratostomafoliatum, deposited in the subtidal zone, had walls that were nearly as thick as N. ostrina; but the leaf-like flattening of these capsules resulted in a much larger surface area to volume ratio. The capsules of both N. ostrina and N. lamellosa maintained or increased their relative rates of oxygen consumption during periods of emersion. However, the difference between the rates of aerial and aquatic oxygen uptake ofN. ostrina were substantially greater than N. lamellosa. During emersion periods there was neither a measurable elimination of carbon dioxide nor evaporative water loss in the capsules of either species. Emersion also resulted in a significant increase in the relative rates of ammonia excretion for both species during subsequent immersion periods. Additionally, there was a large wash out of ammonia that occurred within minutes of re-immersion. In short, during periods of emersion the physicochemical differences between air and water may reduce, but not eliminate, the impact of the diffusive constraints commonly ascribed to encapsulated development. However, if the accumulation of metabolic end products within the capsule is not compensated for this accretion may constrain development. Therefore, the different encapsulation strategies of the muricid gastropods may represent compromises to deal with the combined impacts of these constraints.
Abstracts / Comparative Biochemistry. and Physiology, Part B 126 (2000) S1-S108
EFFECT OF OXIDANTS ON POTASSIUM TRANSPORT IN RED BLOOD CELLS OF HERBIVORES IM. C. M u z y a m b a , 2p. F. S p e a k e & 3j. S. G i b s o n t Veterinary Preclinical Sciences, U n i v e r s i t y o f L i v e r p o o l ; 2Child Health, U n i v e r s i t y o f M a n c h e s t e r ; and 3physiology, St G e o r g e ' s H o s p i t a l M e d i c a l S c h o o l U n i v e r s i t y o f L o n d o n , L o n d o n , S W 1 7 ORE. Animals are exposed to oxidants from a variety of sources. Ingested nitrates, for example found at high levels in contaminated water, heavily fertilised herbiage or Brasssica spp., are converted to nitrites in the anaerobic conditions of the tureen or large intestine. Ialrogenic therapy with oxidant reagents may also occur inadvertently, such as administration of phenylhydrazine or vitamin K to horses and certain dogs. Exposure of red blood cells to oxidants has several important consequences. First, oxidation of haemoglobin to methaemoglohin (metHb) will decrease the oxygencarrying capacity of the cells, and can cause hypoxia of peripheral tissues. Second, oxidants also alter the behaviour of red blood cell membrane solute transporters, especially the inorganic ion co- and counter-transporters. The latter action is important because it will alter red blood cell ion balance and hence cell volume. It may also alter plasma ion concentrations, notably of K +. Thus it has been shown previously that oxidants stimulate the K+-C1" cotransporter (probably KCC1) in red blood cells from a number of different species, including human and sheep, but inhibit the Na+/IT exchanger (3-NHE) of trout (see Gibson et al., 2000, for references). The generation of metHb also activates KCCI in deoxygenated red blood cells of trout and carp, a transporter which is normally inactive at low oxygen tensions. The effect of oxidants on these membrane transporters will depend not only on the effects of oxidants per se, but also, critically, on their ability to respond to physiological stimuli which might further modulate transporter activity, notably O2 tension, cell volume, IT ions and urea. In this study, we used S6Rb+ as a K + congener to investigate the activity of KCCI in red blood cells from horses and cattle in response to the oxidants nitrite and 1-chloro-2,4-dinitrobenzene. We confirm that these oxidants stimulate the activity of KCCI. In addition, we investigated how the transporter was then able to respond to the other major physiological stimuli to which the cells would be exposed in vivo. The transporter was fully responsive to three of these stimuli (cell volume, IT ions and urea), but became progressively less O2-sensitive as the oxidant challenge increased. These findings may be relevant for understanding the pathology of oxidant toxicity and for development of rational chemotherapy to prevent its deleterious effects. This work is supported by The Wellcome Trust. MCM is a Beit Fellow and holder of an ORS award. Gibson, J. S. et al. (2000). J. exp. Biol. 203: 1395-1407.
PHYSIOLOGICAL ADAPTATIONS FOR DEVELOPMENT AMONG SOME INTERTIDAL MURICID G A S T R O P O D S M.S. N e w e l and G.B. Bourne D e p a r t m e n t o f Biological Sciences, U n i v e r s i t y o f Calgary, Calgary, Alberta, C a n a d a T 2 N 1N4 and the Barnfield Marine Station, Barn_field, British C o l u m b i a , C a n a d a V 0 R 1B0 The intertidal zone is a complex and heterogeneous habitat that exposes organisms to highly variable and often harsh environmental conditions. Intertidal gastropods display a wide range of morphological, physiological and behavioural adaptations for periodic emersion, which have been correlated with the tidal heights they inhabit. Similarly, egg capsules deposited in the intertidal zone are also subjected to the stresses associated with emersion. The variety of both the capsule morphology and the life history strategies employed by the muricid gastropods provides an opportunity to study the constraints of encapsulated development in the intertidal zone. Thus, we measured the effects of certain environmental parameters on the egg capsule morphology and several measurements of physiological performance of the capsules ofNucella ostrina and N. lamellosa in comparison to those of other muricid gastropods. An examination of the capsules deposited by the high intertidal Nucella ostrina and the lower intertidal N. lamellosa indicated that despite an extensive overlap in both the wet masses and chamber volumes there were two important differences. The capsules ofN. ostrina had significantly thicker walls and a lower surface area to volume ratio compared to those ofN. lamellosa. In contrast, the capsules of a closely related muricid gastropod Ceratostomafoliatum, deposited in the subtidal zone, had walls that were nearly as thick as N. ostrina; but the leaf-like flattening of these capsules resulted in a much larger surface area to volume ratio. The capsules of both N. ostrina and N. lamellosa maintained or increased their relative rates of oxygen consumption during periods of emersion. However, the difference between the rates of aerial and aquatic oxygen uptake ofN. ostrina were substantially greater than N. lamellosa. During emersion periods there was neither a measurable elimination of carbon dioxide nor evaporative water loss in the capsules of either species. Emersion also resulted in a significant increase in the relative rates of ammonia excretion for both species during subsequent immersion periods. Additionally, there was a large wash out of ammonia that occurred within minutes of re-immersion. In short, during periods of emersion the physicochemical differences between air and water may reduce, but not eliminate, the impact of the diffusive constraints commonly ascribed to encapsulated development. However, if the accumulation of metabolic end products within the capsule is not compensated for this accretion may constrain development. Therefore, the different encapsulation strategies of the muricid gastropods may represent compromises to deal with the combined impacts of these constraints.