By the methods of intracellular microelectrode technique and the bridge circuit for recording the mechanical activity, the effect of external calcium concentration of the cultured chick embryonic heart has been investigated. Trypsin-dispersed cells from the ventricle of 5 days old chick embryos were cultured. The cell clusters became attached to the bottom of cultured-dish. Then, results from trypsin-dispersed cells were compared with those of noncultured intact embryonic hearts. Spontaneous cells were compared with those of non-cultured intact embryonic hearts. Spontaneous cells were discarded and only quiescent cells were driven by electrical field stimulation.
1. The reduction of calcium in the external medium strikingly prolonged the duration of action potential in cultured cells, while the amplitude of mechanical activity was prominently decreased.
2. In the intact embryonic hearts, the configuration of action potential is not significantly affected by the calcium deficient solution. On the other hand, the effect of calcium deficiency on mechanical activity is more dramatic than that in cultured cells. These results suggest that the inward movement of calcium ion through the membrane plays a significant role in the initiation of contraction.
3. The reduced mechanical activity of cultured and intact cells due to calci um deficiency returns to its normal level by the application of g-strophanthin, but the recovery rate was larger in cultured cells.