Inotropic effects of different calcium ion concentration on the embryonic chick ventricle. Comparison of single cultured cells and intact muscle strips.

The effects of changes in the calcium ion concentration in the medium bathin single beating cultured chick embryo ventricular cells were determined using an electro-optical monitoring technique for measuring the amplitude and velocity of cell wall motion. Although single cells showed significant decreases in the amplitude and velocity of cell wall motion during contraction when the calcium ion concentration was lowered from 1.8 mM to 0.9 mM, there were no significant changes in these parameters when the concentration was increased from 1.8 mM to 3.6 mM, and the magnitude of this response increased with increasing embryonic age. These results suggest that there is a reduced positive inotropic responsiveness in young chick embryo ventricular cells, which is particularly marked in the single cultured cell preparation because of the tendency of culturing techniques to select out immature cell populations.