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This Article Full Text Full Text (PDF) Supplemental Figures All Versions of this Article: 297/3/R756    most recent 00102.2009v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Stecyk, J. A. W. Articles by Pörtner, H.-O. PubMed PubMed Citation Articles by Stecyk, J. A. W. Articles by Pörtner, H.-O.

ARTICLES

Correlation of cardiac performance with cellular energetic components in the oxygen-deprived turtle heart

¹Department of Zoology, University of British Columbia, Vancouver, BC, Canada; ²Integrative Ecophysiology, Alfred-Wegener-Institute for Marine and Polar Research, Bremerhaven, Germany; ³Zoophysiology, Department of Biological Sciences, University of Aarhus, Aarhus, Denmark; and ⁴Department of Zoology and Faculty of Food and Land Systems, University of British Columbia, Vancouver, BC, Canada

Submitted 13 February 2009 ; accepted in final form 6 July 2009

The relationship between cardiac energy metabolism and the depression of myocardial performance during oxygen deprivation has remained enigmatic. Here, we combine in vivo ³¹P-NMR spectroscopy and MRI to provide the first temporal profile of in vivo cardiac energetics and cardiac performance of an anoxia-tolerant vertebrate, the freshwater turtle (Trachemys scripta) during long-term anoxia exposure (3 h at 21°C and 11 days at 5°C). During anoxia, phosphocreatine (PCr), unbound levels of inorganic phosphate (effective P_i^2–), intracellular pH (pH_i), and free energy of ATP hydrolysis (dG/d) exhibited asymptotic patterns of change, indicating that turtle myocardial high-energy phosphate metabolism and energetic state are reset to new, reduced steady states during long-term anoxia exposure. At 21°C, anoxia caused a reduction in pH_i from 7.40 to 7.01, a 69% decrease in PCr and a doubling of effective P_i^2–. ATP content remained unchanged, but the free energy of ATP hydrolysis (dG/d) decreased from –59.6 to –52.5 kJ/mol. Even so, none of these cellular changes correlated with the anoxic depression of cardiac performance, suggesting that autonomic cardiac regulation may override putative cellular feedback mechanisms. In contrast, during anoxia at 5°C, when autonomic cardiac control is severely blunted, the decrease of pH_i from 7.66 to 7.12, 1.9-fold increase of effective P_i^2–, and 6.4 kJ/mol decrease of dG/d from –53.8 to –47.4 kJ/mol were significantly correlated to the anoxic depression of cardiac performance. Our results provide the first evidence for a close, long-term coordination of functional cardiac changes with cellular energy status in a vertebrate, with a potential for autonomic control to override these immediate relationships.

high-energy phosphate metabolism; anoxic turtle cardiac performance; in vivo magnetic resonance spectroscopy