Ca2+ removal mechanisms in mouse embryonic stem cell-derived cardiomyocytes

Area of Science:

• Cardiovascular Research
• Cellular Physiology
• Developmental Biology

Background:

• In adult cardiomyocytes, sarcoplasmic reticulum (SR) Ca(2+)-ATPase (SERCA) is crucial for cytosolic Ca(2+) decline, surpassing the sarcolemmal Na(+)/Ca(2+) exchanger (NCX).
• The roles of SERCA and NCX in Ca(2+) removal during early heart development remain unclear.

Purpose of the Study:

• To investigate the functional contributions of Ca(2+) transporters to cytosolic Ca(2+) decline during early cardiogenesis.
• To model early heart development using mouse embryonic stem cell-derived cardiomyocytes (mESCMs) at various differentiation stages.

Main Methods:

• Utilized mESCMs at different differentiation stages to model early cardiogenesis.
• Employed dynamical analysis of transient decay phases in normal and Na(+)-free solutions.
• Assessed Ca(2+) transporter function by suppressing SR function using ryanodine receptor-null mESCMs and pharmacological inhibitors (ryanodine, thapsigargin).

Main Results:

• SERCA accounted for ~76% of Ca(2+) removal in early-stage mESCMs, with NCX contributing ~21%.
• At late differentiation stages, SERCA's contribution increased to ~88%, while NCX decreased to ~10%.
• NCX's role in Ca(2+) decline was more prominent during the slow terminal decay phase, especially when SR function was inhibited.

Conclusions:

• Rapid cytosolic Ca(2+) decline in differentiating cardiomyocytes is primarily mediated by SR uptake, even at early stages.
• NCX serves as the main Ca(2+) remover when SR function is compromised.
• SR plays a vital role in regulating cytosolic Ca(2+) homeostasis throughout cardiomyocyte differentiation.