Na⁺/K⁺-ATPase activity in the anoxic turtle (Trachemys scripta) brain at different acclimation temperature

Area of Science:

• Physiology
• Biochemistry
• Neuroscience

Background:

• Prolonged anoxia survival depends on balancing cellular ATP demand and supply, especially in the brain.
• The anoxia-tolerant red-eared slider turtle (Trachemys scripta) provides a model for studying brain adaptation to anoxia.

Purpose of the Study:

• To investigate ATP demand in the turtle brain during prolonged anoxia.
• To quantify Na⁺-K⁺-ATPase units and their molecular activity in turtle brains under varying temperature and oxygen conditions.

Main Methods:

• Comparing Na⁺-K⁺-ATPase activity and density in turtle brain tissue.
• Assessing changes under normoxia and anoxia at 21°C and 5°C.
• Analyzing α-subunit composition to understand pump activity regulation.

Main Results:

• Na⁺-K⁺-ATPase activity and density were similar between 21°C and 5°C in normoxic turtles.
• Anoxia at 21°C did not alter Na⁺-K⁺-ATPase activity or density.
• Prolonged anoxia at 5°C reduced Na⁺-K⁺-ATPase activity by 55% due to a 50% decrease in pump units, with no change in individual pump activity or α-subunit composition.

Conclusions:

• Findings support the "channel arrest" hypothesis for reducing brain ATP demand during prolonged anoxia.
• This mechanism is crucial for overwintering survival in anoxic, low-temperature environments.
• The study highlights a key adaptation in anoxia-tolerant turtles for surviving extreme conditions.