The anatomy of fish is such that a single ventricle pumps blood directly into the gills for oxygenation before it is distributed to the rest of the tissues. The ventricle consists of a spongy endocardium, which in some cases is surrounded by a compact epicardium. Many fish species, including the Atl...
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.599.1709 http://jeb.biologists.org/content/207/11/1865.full.pdf |
| Summary: | The anatomy of fish is such that a single ventricle pumps blood directly into the gills for oxygenation before it is distributed to the rest of the tissues. The ventricle consists of a spongy endocardium, which in some cases is surrounded by a compact epicardium. Many fish species, including the Atlantic cod (Gadus morhua), contain only the spongy layer, which lacks a coronary supply (Farrell and Jones, 1992). Since there are no coronary arteries providing oxygenated blood to the heart, the only metabolic support the heart receives is from the partially oxygenated venous blood returning directly from the systemic circulation to the ventricular lumen (Santer, 1985). The myocytes must acquire oxygen, ions and nutrients from the blood flowing between the trabeculae and therefore are subjected to fluctuating oxygen supply (Satchell, 1991). Oxygen delivery to the heart can be reduced simply by living in conditions of low environmental oxygen or by actively swimming. Previous studies have shown that Atlantic cod hearts are reasonably tolerant to oxygen deprivation. For example, when isolated ventricle strips were subjected to 35·min of anoxia, they continued to perform at ~35 % of their initial force at 30·min (MacCormack and Driedzic, 2002). This attribute, along with the lack of coronary arteries, makes this tissue an excellent model system to investigate factors that control anaerobic metabolism, such as glucose uptake under steady-state conditions. Myocardial glucose metabolism in vertebrates is primarily dependent on the uptake of extracellular glucose. Glucose enters the cell and is phosphorylated by hexokinase to glucose-6-phosphate (G-6-P), which in turn enters the glycolytic pathway common to both glucose breakdown and glycogenolysis. In the rat heart, the maximal in vitro activity of hexokinase is about 5-fold greater than the maximal rate of glucose transport (Randle and Tubbs, 1979). Glucose uptake is the rate-limiting step for the mammalian heart under anoxia; |
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