The regulation of the intracellular sodium ion concentration in cultured chick embryo heart cells.

Using digital imaging microscopy with the fluorescent indicator sodium-binding benzofuran isophtalate, we examined the cytosolic Na+ concentration ([Na+]i) in individual chick embryo heart cells. Inhibition of the Na(+)-H+ exchanger using Na(+)-free (Li+ substituted) medium and inhibition of the Na(+)-efflux through the Na(+)-Ca2+ exchanger using Ca(2+)-free medium didn't change the [Na+]i. The opening of voltage-dependent Na+ channels with veratridine (150 micrograms/ml) and inhibition of the Na(+)-K(+)-Cl(-)-cotransporter with bumetanide (10 microM) led to an increase in [Na+]i by 107% and 86%, respectively, suggesting that the Na+ channels and the Na(+)-K(+)-Cl- cotransporter predominantly regulate the [Na+]i in cultured chick embryo heart cells.