Elevated Ca2+ ATPase (SERCA2) activity in tuna hearts: comparative aspects of temperature dependence

Area of Science:

• Marine Biology
• Comparative Physiology
• Biochemistry

Background:

• Tunas possess remarkable physiology, including high metabolic rates and cardiac performance.
• Their hearts operate at ambient temperatures, unlike some other tuna species that retain metabolic heat.
• Cardiac excitation-contraction (E-C) coupling relies on proteins like the cardiac sarcoplasmic reticulum Ca2+-ATPase (SERCA2).

Purpose of the Study:

• To investigate the physiological basis for enhanced cardiac performance in tunas.
• To compare calcium transport rates and SERCA2 expression across different tuna species.
• To elucidate the role of SERCA2 in the cardiac function of bluefin tuna.

Main Methods:

• Measurement of oxalate-supported Ca2+-uptake in atrial SR vesicles from four tuna species.
• Analysis of temperature dependency for Ca2+-uptake and ATP hydrolysis.
• Western blot analysis to quantify SERCA2 and RyR protein expression.

Main Results:

• Bluefin tuna displayed at least twofold higher atrial Ca2+-uptake compared to other tuna species between 5 and 30°C.
• Maximum atrial Ca2+-uptake in bluefin tuna was recorded at 30°C.
• Significantly higher SERCA2 content was observed in bluefin tuna atrial tissues, correlating with increased Ca2+ uptake.

Conclusions:

• Elevated SERCA2 activity in bluefin tuna hearts is a key factor in their high cardiac performance.
• These adaptations are crucial for maintaining higher heart rates and endothermy in bluefin tuna.
• SERCA2 upregulation represents a significant evolutionary adaptation in bluefin tuna cardiac myocytes.