Passive Ca2+ overload in H9c2 cardiac myoblasts: Assessment of cellular damage and cytosolic Ca2+ transients

Increase of resting Ca2+ levels and amplitude of vasopressin-induced Ca2+ transients were observed when cells in serum-free medium were exposed to 5 mM Ca2+ for 2 h. Small effect on cell viability was also observed. A rapid cytotoxic effect was developed in the presence of 10 mM Ca2+ and absence of serum. However, cells exposed to 10 mM Ca2+ in the presence of serum were protected from damage for at least 2 days. Resting Ca2+ levels and cytosolic Ca2+ transients in serum-containing medium with 10 mM Ca2+ displayed lower increases and a tendency to recover control values. When serum was absent, cells preincubated with 10 mM Ca2+ were more sensitive to thapsigargin-induced damage than cells preincubated with lower Ca2+. The sensitivity was similar when serum was present. Tolerance to high Ca2+ in the presence of serum was linked to potentiation of the mitochondrial Ca2+ entry to decrease the sarcoplasmic reticulum Ca2+ overload.