Use este identificador para citar ou linkar para este item: http://repositorio.inpa.gov.br/handle/123/936
Título: RAPID REGULATION OF NA+ AND AMMONIA FLUXES IN RESPONSE TO ACUTE ENVIRONMENTAL HYPOXIA IN THE AMAZONIAN OSCAR, ASTRONOTUS OCELLATUS. AM.
Autor(es): Christopher Michael Wood
Makiko Kajimura
Katherine A Sloman
Graham R Scott
Patrick J Walsh
Vera Maria Fonseca de Almeida e Val
Adalberto Luis Val
ISSN: 0363-6119
Revista: American Journal of Physiology. Regulatory, Integrative and Comparative Physiology
Volume: 292
Resumo: The Amazonian oscar is extremely resistant to hypoxia, and tolerance scales with size. Overall, ionoregulatory responses of small (∼15 g) and large oscars (∼200 g) to hypoxia were qualitatively similar, but the latter were more effective. Large oscars exhibited a rapid reduction in unidirectional Na+ uptake rate at the gills during acute hypoxia (Po2 ∼10 mmHg), which intensified with time (7 or 8 h); Na+ efflux rates were also reduced, so net balance was little affected. The inhibitions were virtually immediate (1st h) and preceded a later 60% reduction (at 3 h) in gill Na+-K+-ATPase activity, reflected in a 60% reduction in maximum Na+ uptake capacity without change in affinity (Km) for Na+. Upon acute restoration of normoxia, recovery of Na+ uptake was delayed for 1 h. These data suggest that dual mechanisms may be involved (e.g., immediate effects of O2 availability on transporters, channels, or permeability, slower effects of Na+-K+-ATPase regulation). Ammonia excretion appeared to be linked indirectly to Na+ uptake, exhibiting a Michaelis-Menten relationship with external [Na+], but the Km was less than for Na+ uptake. During hypoxia, ammonia excretion fell in a similar manner to Na+ fluxes, with a delayed recovery upon normoxia restoration, but the relationship with [Na+] was blocked. Reductions in ammonia excretion were greater than in urea excretion. Plasma ammonia rose moderately over 3 h hypoxia, suggesting that inhibition of excretion was greater than inhibition of ammonia production. Overall, the oscar maintains excellent homeostasis of ionoregulation and N-balance during severe hypoxia.
URI: http://repositorio.inpa.gov.br/handle/123/936
ISSN: 0363-6119
DOI: https://dx.doi.org/10.1152/ajpregu.00640.2006
Aparece nas coleções:Coordenação de Biodiversidade (CBIO)

Arquivos associados a este item:
Não existem arquivos associados a este item.


Este item está licenciada sob uma Licença Creative Commons Creative Commons