Passive Ca 2+ overload in H9c2 cardiac myoblasts: Assessment of cellular damage and cytosolic Ca 2+ transients (original) (raw)

Increase of resting Ca 2+ levels and amplitude of vasopressin-induced Ca 2+ transients were observed when cells in serum-free medium were exposed to 5 mM Ca 2+ for 2 h. Small effect on cell viability was also observed. A rapid cytotoxic effect was developed in the presence of 10 mM Ca 2+ and absence of serum. However, cells exposed to 10 mM Ca 2+ in the presence of serum were protected from damage for at least 2 days. Resting Ca 2+ levels and cytosolic Ca 2+ transients in serum-containing medium with 10 mM Ca 2+ displayed lower increases and a tendency to recover control values. When serum was absent, cells preincubated with 10 mM Ca 2+ were more sensitive to thapsigargin-induced damage than cells preincubated with lower Ca 2+ . The sensitivity was similar when serum was present. Tolerance to high Ca 2+ in the presence of serum was linked to potentiation of the mitochondrial Ca 2+ entry to decrease the sarcoplasmic reticulum Ca 2+ overload. reticulum Ca 2+ -ATPase; DMEM, Dulbecco's modified Eagle's medium; AM, acetoxymethyl; MTT, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide; Ru360, oxygen-bridged dinuclear ruthenium amine complex; ECM, extracellular medium; HEPES, 4-(2-hydroxyethyl)piperazine-1-ethanesulfonic acid; PBS, phosphate-buffered saline; EGTA, ethylene glycol-bis(b-aminoethyl ether)-N,N,N 0 ,N 0 -tetraacetic acid; ROIs, regions of interest; k VP , k TG and k TG+Ru , first-order rate constants for Ca 2+ transient decays induced by VP, TG or TG plus Ru360, respectively.