Ultrastructural response of cultured heart cells to calcium depletion and repletion

Calcium-free incubation followed by exposure to Ca produces ultrastructural damage in the intact myocardium—a phenomenon known as the Ca paradox. Controversy exists as to whether the observed Ca overload during Ca repletion is a primary cause for, or a secondary consequence of, sarcolemmal disruption and cell injury. In these experiments cultured embryonic chick heart cells have been subjected to Ca depletion/repletion to explore the structural, transport and metabolic mechanisms by which cells may be irreversibly damaged. Monolayer muscle enriched cell cultures were prepared by serial trypsin-disaggregation of 11-day old chick embryo hearts. Cells were incubated for 10 or 120 min in Ca-free (1 mM EGTA) Hepes-buffered salt solution (pH 7.4) followed by incubation for 60 or 180 min in the same solution containing 1 mM Ca. In another series of experiments, the mitochondrial uncoupling agent carbonyl cyanide chlorophenylhydrazone (CCCP, 10 μM ) was added during depletion and repletion.