Inhibition of Vascular Smooth Muscle Cell K + Currents by Tyrosine Kinase Inhibitors Genistein and ST 638

Abstract

The whole-cell patch-clamp technique was used to characterize the effects of several tyrosine kinase inhibitors on the voltage-gated K⁺ current (I_K) in rat and rabbit pulmonary artery cells. I_K was blocked in a dose-dependent manner by genistein (20 to 100 μmol/L) and ST 638 (0.5 to 40 μmol/L) but not by the inactive genistein analogue diadzein (100 μmol/L). This inhibition was not significantly altered when ATP was excluded from the patch pipette or when it was replaced by the poor tyrosine kinase substrate ATP-γ-S. The inhibition was also unaffected by inclusion of the tyrosine phosphatase inhibitor orthovanadate in either the bath (0.5 mmol/L) or pipette (0.2 mmol/L) solutions. In the rat, I_K ordinarily inactivated negligibly over 300 ms. In the presence of 10 μmol/L ST 638, however, I_K reached a peak ≈5 ms after depolarization (to +60 mV) and then decayed markedly. In the rabbit, I_K demonstrated a prominent rapidly decaying initial component that was only slightly inhibited by ST 638, which preferentially blocked the sustained current; genistein showed the opposite selectivity. These observations indicated that I_K blockade by genistein and ST 638 was not mediated by an inhibition of tyrosine kinase activity and further suggested that in both types of cells genistein and ST 638 preferentially blocked rapidly and slowly inactivating components of I_K, respectively.