MORPHOLOGICAL CHANGES OF CULTURED MYOCARDIAL CELLS DUE TO CHANGE IN EXTRACELLULAR CALCIUM ION CONCENTRATION.

Increase in the extracellular Ca concentration from low (≤ 10 M) to normal (10 M) caused morphological changes of cultured myocardial cells obtained from fetal mouse heart. The extracellular Na and K concentrations of the normal medium (10 M Ca ) did not significantly affect the genesis of these morphological changes. Like Ca , Ba and Sr , but not Mg , Co or Ni , could induce morphological changes. Increase in the extracellular Ca concentration from 10 M to 10 M also caused excess uptake of Ca by cultured myocardial cells. B-16CW 1 cells, which did not show these morphological changes, did not take up excess Ca on this treatment. Treatments, such as addition of verapamil or incubation at pH 6.3, which reduced the genesis of morphological changes, reduced the rate of Ca uptake by myocardial cells. These facts show that the morphological changes of myocardial cells induced by increasing the extracellular Ca concentration from low to normal are due to excess uptake of Ca by the myocardial cells. The morphological changes of cultured myocardial cells induced by increasing the extracellular Ca concentration from low to normal were reversed on further incubation of the cells in medium with or without Ca .