Chick embryo heart cells with high and low intracellular calcium concentrations respond differently to ouabain

Abstract

In cell cultures of 10-day-old chick embryo hearts, we found two cell populations, one with high intracellular calcium concentration ([Ca 2+] i) of 116 ± 34 nM (S.E., high [Ca 2+] i cells, n = 154) and another one with low [Ca 2+] i of 46 ± 14 nM [Ca 2+] i (S.E., low [Ca 2+] i cells, n = 171), as revealed by fura-2 digital imaging fluorescence microscopy. The proportion of the high [Ca 2+] i cells varied as a function of the cell density from 10–60% of all cells. Histochemical staining of the cells showed that cells with high and low [Ca 2+] i did not represent differences between muscle and non-muscle cells. When the cells were exposed to different concentrations of ouabain, the high [Ca 2+] i cells showed a half maximal effect at 2 · 10 −9 M ouabain, but only a small increase in [Ca 2+] i of 30%. The low [Ca 2+] i cells reached their half maximal increase in [Ca 2+] i at 4 · 10 −8 M ouabain. A second increase in [Ca 2+] i in this cell type was observed between 10 −6 and 10 −5 M ouabain. Toxic concentrations of ouabain produced an excessive increase in [Ca 2+] i in low [Ca 2+] i cells, whereas high [Ca 2+] i cells showed morphological degeneration due to their higher sensitivity to ouabain. In conclusion, we demonstrate that chick embryo heart contains cells with high and low [Ca 2+] i which show differences in the sensitivity of their sodium pumps to cardiac glycosides.