Voltage-energized Calcium-sensitive ATP Production by Mitochondria

Area of Science:

• Biochemistry
• Cellular Biology
• Mitochondrial Function

Background:

• Mitochondrial ATP production is vital for multicellular organisms but its regulation is not fully understood.
• Calcium ions (Ca2+) play a role in cellular signaling and energy metabolism.
• The mitochondrial calcium uniporter (MCU) is a key protein complex for Ca2+ transport into the mitochondrial matrix.

Purpose of the Study:

• To investigate the molecular mechanisms controlling ATP production in the heart.
• To elucidate the framework for Ca2+-dependent regulation of mitochondrial ATP synthesis.
• To compare the function of cardiac and skeletal muscle MCU and ATP synthase.

Main Methods:

• Investigated Ca2+ entry into the mitochondrial matrix via the MCU in heart cells.
• Analyzed the influence of matrix Ca2+ on pyruvate and glutamate dehydrogenase activity.
• Examined the relationship between inner mitochondrial membrane potential (ΔΨm) and ATP production.
• Compared the voltage dependence of ATP synthase in cardiac muscle, skeletal muscle, and bacteria.

Main Results:

• Cardiac MCU Ca2+ entry lacks a cytosolic Ca2+ threshold and gating function, directly impacting ΔΨm.
• Matrix Ca2+ regulates ATP production by modulating dehydrogenase activity, not by affecting ATP Synthase or Electron Transport Chain complexes.
• Cardiac ATP synthase exhibits a unique voltage dependence, distinct from bacterial ATP synthase, with a different ΔΨm threshold and a concave-upward, non-saturating profile.
• Skeletal muscle MCU function differs from cardiac MCU, but ATP synthase voltage dependence is conserved between cardiac and skeletal muscle.

Conclusions:

• Cardiac ATP production is regulated by matrix Ca2+ through modulation of dehydrogenase activity and inner mitochondrial membrane potential.
• Cardiac ATP synthase displays a distinct voltage-dependent behavior compared to bacterial ATP synthase.
• While MCU-mediated Ca2+ signaling is tissue-specific, the ΔΨm control of ATP synthase appears conserved across mammalian tissues but differs from bacterial mechanisms.