Effect of protein tyrosine kinase inhibitors on the current through the CaV3.1 channel

In the present study, we have investigated the effects of protein tyrosine kinase (PTK) inhibitors on the CaV3.1 calcium channel stably transfected in HEK293 cells using the whole-cell configuration of the patch–clamp technique. We have tested two different tyrosine kinase inhibitors, genistein and tyrphostin AG213, and their inactive analogs, genistin and tyrphostin AG9. Bath application of genistein, but not genistin, decreased the T-type calcium current amplitude in a concentration-dependent manner with an IC50 of 24.7 ± 2.0 μM. This effect of genistein was accompanied by deceleration of channel activation and acceleration of channel inactivation. Intracellular application of neither genistein nor genistin had a significant effect on the calcium current. Extracellular application of 50 μM tyrphostin AG213 and its inactive analogue, tyrphostin AG9, did not affect the current through the CaV3.1 channel. The effect of genistein on the channel was also not affected by the presence of catalytically active PTK, p60c-src inside the cell. We have concluded that genistein directly inhibited the channel. This mechanism does not involve a PTK-dependent pathway. The alteration of the channel kinetics by genistein suggests an interaction with the voltage sensor of the channel together with the channel pore occlusion.