| Autor: |
Sephton, Dawn, Bailey, John, Driedzic, William |
| Zdroj: |
Journal of Comparative Physiology B: Biochemical, Systemic & Environmental Physiology; Dec1990, Vol. 160 Issue 5, p511-518, 8p |
| Abstrakt: |
The impact of an acute temperature transition between 5 °C and 15 °C on energy metabolism and performance of sea raven ( Hemitripterus americanus) heart was assessed. Maximal in vitro activity of hexokinase was 1.2 and 3.7 μmol · min · g at 5 °C and 15 °C, respectively. Carnitine palmitoyl transferase and carnitine palmitoleoyl transferase activities were 0.07 μmol · min · g at 15 °C and declined substantially at 5 °C. Oxygen consumption and power output of perfused isolated hearts offered glucose alone as a metabolic fuel decreased significantly between 15 °C and 5 °C. When palmitoleate was included in the perfusion medium, oxygen consumption and power development remained constant between 15 °C and 5 °C, suggesting that glucose alone was not an adequate metabolic fuel at low temperature. However, maximal in vitro activity of HK implied that the catalytic potential at this locus was quite capable of meeting demands of carbon flow, while the maximal in vitro activity of the carnitine acyl CoA transferases implied that fatty acid metabolism should be greatly compromised at low temperatures. In an effort to resolve the contradiction, hearts were perfused with medium containing C-glucose or C-palmitate. Rates of CO production from labelled metabolic fuels could account for only about 2% of the oxygen consumption rates. Most of the label from C-glucose was incorporated into the glycogen and lipid fractions and label from C-palmitate was incorporated into the lipid fraction. The net incorporation rates of label into intracellular pools were temperature insensitive over the range 5-15 °C. The incorporation of exogenous glucose into the lipid fraction suggests that activity of the entire glycolytic pathway was maintained over the temperature range. Thus, the relatively low rate of oxygen consumption of hearts perfused with glucose alone as an exogenous substrate cannot be attributed to a limitation of glucose catabolism. The alternative explanation is that the presence of fatty acids induces an increase in oxygen consumption, especially at 5 °C. It is speculated that this is due to alterations in Ca balance. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
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