Anoxia and ischemia tolerance in turtle hearts

Area of Science:

• Cardiovascular Physiology
• Comparative Physiology
• Biochemistry

Background:

• Turtle hearts possess exceptional tolerance to anoxia and ischemia.
• The underlying mechanisms for this resilience are not fully understood.
• A significant adaptation involves a rapid decrease in metabolic rate during anoxia.

Purpose of the Study:

• To investigate the physiological and biochemical mechanisms behind anoxia and ischemia tolerance in turtle hearts.
• To compare the anoxic responses of painted turtle (Chrysemys picta) and softshelled turtle (Trionyx spinifer) hearts.
• To explore the potential role of phosphodiesters (PDEs) in anoxia tolerance.

Main Methods:

• Nuclear magnetic resonance (NMR) measurements to assess high-energy phosphates (e.g., phosphocreatine [PCr], ATP) and intracellular pH (pHi).
• In vivo and isolated heart studies to evaluate cardiac performance and tolerance to anoxia/ischemia.
• Analysis of phosphodiester (PDE) concentrations.

Main Results:

• Painted turtle hearts exhibit a rapid decrease in PCr to 50% during anoxia, with ATP levels maintained and pHi decreasing slightly.
• Softshelled turtle hearts, while more sensitive in vivo, show similar anoxia tolerance in isolated preparations compared to painted turtle hearts.
• Little difference was observed in cardiac performance, high-energy phosphates, or pHi between species during ischemia.

Conclusions:

• Turtle hearts maintain metabolic control, acid-base, and phospholipid homeostasis during anoxia/ischemia.
• These interdependent physiological processes contribute to anoxia and ischemia tolerance.
• Further research is needed to elucidate the complex interactions of these mechanisms and the specific role of PDEs.