Scientific Journal Article Summary
Elevated Ca2+ ATPase (SERCA2) activity in tuna hearts: Comparative aspects of temperature dependence.
Pedro C. Castilho, Ana M. Landeira-Fernandez, Jeffery Morrissette, Barbara A. Block
Comparative Biochemistry and Physiology, Part A (2007) 148:124–132
Bluefin tuna are renowned for their warm-bodiedness and can maintain elevated tissue temperatures in their brain, eyes, internal organs and swimming muscles. TGF tagging has recorded body temperatures over 50ºF above that of the surrounding seawater. Interestingly, the bluefin heart is not warmed but rather remains at the same temperature as the water. Nevertheless, bluefin tuna express elevated metabolic and cardiovascular performance, stimulating numerous questions about how the heart can operate so efficiently across such a wide temperature range.
TGF scientists analyzed calcium uptake from a cellular component known as the sarcoplasmic reticulum in the atria (tuna have two heart chambers – one atrium and one ventricle) of four tuna species. They found that bluefin tuna have at least two fold higher calcium uptake, which increases cardiac contraction and therefore cardiac performance, than three other tuna species at all temperatures tested. This may help to explain the niche expansion of bluefin tuna into colder, northern waters as compared to other tuna species. Bluefin tuna also had higher quantities of enzymes known to process calcium during heart contractions as compared to the other three species, providing the evolutionary mechanism for bluefin’s cold-tolerance and superior cardiac performance. Superior cardiac performance allows greater oxygenation of tissues, which is consistent with the bluefin’s high metabolic rate relative to other tunas.
In all four species cardiac performance showed a bell-shaped curve according to temperature, decreasing significantly both as temperature increased above and dropped below 86°F. The latter may partially explain why bluefin tuna repeatedly ascend to warmer, shallower waters when feeding in deep water, and the former may help to explain why bluefin tuna show stress in the warm waters of the
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Figure 1. Calcium uptake, an indicator of cardiac performance, in the atrial sarcoplasmic reticulum according to temperature for 4 tuna species: (♦) bluefin tuna; (□) albacore tuna; (▴) yellowfin tuna; (○) bigeye tuna.
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