Synergistic effect of acidification and hypoxia: an in vivo 31p-nmr
and respirometric study in fishes.
Ginneken, Vincent Van, Guido Van Den Thillart, Albert Addink, Cees
Erkelens.
Animal Physiology, Institute of Evolutionary and Ecological
Sciences (EEW), Department of Biology, Gorlaeus laboratories,
Einsteinweg 55, P.O.Box 9502,
APStracts 3:0218R, 1996.
We used 31P-nuclear magnetic resonance (NMR) spectroscopy to measure
intracellular pH (pHi) and high-energy phosphate levels of white
muscle of the fish species tilapia (Oreochromis mossambicus) during
exposure to the stressors hypoxia and water acidification separately
and simultaneously. The protocol for the graded hypoxia load was
100%, 40%, 30%, 20%, 10%, 5% and 3% Airsatura tion, one hour at each
level. For environmental acidosis the water was lowered from pH 7.6
to pH 4.0, transition time 6 hours, exposure time approximately 11
hours. All protocols were followed by 6 hours reoxygenation at 20oC.
We also measured total oxygen consumption of the animal. The results
of this in vivo study revealed that environmental acidification had
no effect on oxygen consumption, intracellular pH or phosphocreatine
(PCr) depletion. Hypoxia causes moderate changes of these parameters,
and fast and complete recovery during reoxygenation. In contrast, the
combination of environmental acidosis and hypoxia resulted in 50%
mortality, increased depletion of the PCr pool and a retarded
recovery of the pHi during reoxygena tion compared to the group with
hypoxia as a single stressor. The combination of environmental
acidification and hypoxia has a more profound effect and works
synergistically compared to the conditions imposed separately. To
investigate whether an adaptation response occurred during chronic
exposure to environmental acidification, animals were exposed for 6
weeks to pH 4.0 prior to experimentation. The pHi in the white muscle
dropped from 7.2 (control group) to 6.9 during this period while no
effect was found in the phosphorylated compounds and oxygen
consumption. Therefore it is concluded that no adaptation response
occurs in animals long term exposed to environ mental acidosis.
Received 21 August 1995; accepted in final form 28 May 1996.
APS Manuscript Number R523-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 28 June 96