Adrenaline keep tuna hearts pumping during extreme temperature drops

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Adrenaline keep tuna hearts pumping during extreme temperature drops

February 11, 2015 - 11:20
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Scientists have discovered how prized bluefin tuna keep their hearts pumping during temperature changes that would stop a human heart.

Pacific bluefin tuna are unique amongst bony fish as they are endothermic (warm bodied) and can raise their core body temperature to 20°C above that of the surrounding water.

These animals are also capable of diving to depths of more than 1000 meter where the water is frigid. This chills the heart because it receives blood directly from the gills which mirrors water temperature. During deep dives their body temperature stays warm but their heart temperature can fall by 15°C within minutes. In other animals, humans included, this would stop the heart.

Tunas are at a unique place in bony fish evolution” says Professor Barbara Block at Stanford. “Their bodies are almost like ours - endothermic, but their heart is running as all fish at ambient temperatures. How the heart keeps pumping as the fish moves into the colder water is the key to their expanded global range.”

To study the problem the team, including Dr Gina Galli from Manchester’s Medical and Human Sciences Faculty, worked at the Tuna Research and Conservation Center at Stanford University. Tracking bluefin tuna in the wild using archival tags, the researchers were able to measure three things: the depth of the fish; its internal body temperature and the ambient water temperature.

Dr Shiels explains their findings: “We discovered that changes in the heart beat due to the temperate, coupled with the stimulation of adrenalin by diving adjusts the electrical activity of the heart cells to maintain the constant calcium cycling needed to keep pumping. If we went through this temperature change our calcium cycling would be disrupted, our hearts would stop beating and we would die.”

From work at sea and in the lab we now know the fish hearts slow as they cool and as they resurfaced it sped up. Our findings suggest adrenalin, activated by the stress of diving, plays a key role in maintaining the heart’s capacity to supply the body with oxygen.

Professor Barbara Block, Stanford University

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