Genistein inhibition of fast Na+ current in uterine leiomyosarcoma cells is independent of tyrosine kinase inhibition.

Possible regulation of fast Na+ channels by tyrosine kinase was examined in human uterine smooth muscle cell line, using whole-cell voltage clamp (at a holding potential of - 90 mV). Bath application of genistein, an inhibitor tyrosine kinase, decreased the fast Na+ current (INa(f)) dose-dependently. The maximal inhibition of INa(f) was 98%, and the concentration for half-maximal inhibition (IC50) was 9 microM. The effect of genistein was rapidly reversible. Daidzein, an inactive analog of genistein, had a similar inhibitory effect on INa(f). These results suggest that the fast Na+ channels in uterine sarcoma cells may be directly blocked by genistein and daidzein, i.e., their effect may be independent of tyrosine kinase inhibition.