Hearts that can Beat Without Oxygen

For most vertebrates, the absence of oxygen (anoxia) quickly leads to death. For example, most vertebrates (including humans) can only hold their breath for a matter of minutes. Remarkably, however, freshwater turtles of the genera Trachemys and Chrysemys can survive without oxygen under water for periods lasting several months. These animals have evolved a wide range of metabolic strategies and adaptations that allow them to avoid, regulate, or mitigate the negative effects of anoxia and reoxygenation on cell function. Through the strategies they use, turtles are excellent model species to reveal novel drug targets for the treatment of oxygen-related cardiac diseases in humans.

How does the Turtle Heart Beat Without Oxygen for Several Months?

Turtles experience anoxia throughout their lifetime through activities like breath-hold diving and winter hibernation
Some turtles can hibernate under ice-covered lakes and ponds without oxygen for up to 6 months!
Compared to other vertebrates, turtles are over 10,000 times more tolerant of anoxia
It's not just a case of being ectothermic, because other ectotherms can only last up to 100 mins without oxygen

Turtles use many strategies to survive without oxygen, including:
- Metabolic suppression: reducing metabolism by 700 fold to match ATP supply to demand
- Shell buffering: breaking down carbonates within their shell to buffer protons and maintain pH
- Suppression of reactive oxygen species (ROS): good antioxidant defences and mechanisms that supress the production of ROS
Understanding the mechanisms that allow turtles to live without oxygen has far-reaching clinical benefits which could reveal drug targets for oxygen-related diseases of the human heart