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

Increase in the extracellular Ca2+ concentration from low (≤ 10-7 M) to normal (10-3 M) caused morphological changes of cultured myocardial cells obtained from fetal mouse heart. The extracellular Na+ and K+ concentrations of the normal medium (10-3 M Ca2+ ) did not significantly affect the genesis of these morphological changes. Like Ca2+ , Ba2+ and Sr2+ , but not Mg2+ , Co2+ or Ni2+ , could induce morphological changes. Increase in the extracellular Ca2+ concentration from 10-8 M to 10-3 M also caused excess uptake of 45 Ca2+ by cultured myocardial cells. B-16CW 1 cells, which did not show these morphological changes, did not take up excess 45 Ca2+ 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 45 Ca2+ uptake by myocardial cells. These facts show that the morphological changes of myocardial cells induced by increasing the extracellular Ca2+ concentration from low to normal are due to excess uptake of Ca2+ by the myocardial cells. The morphological changes of cultured myocardial cells induced by increasing the extracellular Ca2+ concentration from low to normal were reversed on further incubation of the cells in medium with or without Ca2+ .