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

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Abstract
Increase in the extracellular Ca2+ concentration from low (.ltoreq. 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 45Ca2+ by cultured myocardial cells. B-16 CW 1 [mouse spontaneous melanoma] cells, which did not show these morphological changes, did not take up excess 45Ca2+ 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 45Ca2+ 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+.