Verapamil- and state-dependent effect of 2-aminoethylmethanethiosulphonate (MTSEA) on hK(v)1.3 channels

T-cells usually express voltage-gated K(v) 1.3 channels. These channels are distinguished by their typical C-type inactivation. Therefore, to be able to rationally design drugs specific for the C-type inactivation state that may have therapeutic value in autoimmune disease therapy, it is necessary to identify those amino acids that are accessible for drug binding in C-type inactivated channels.

The influence of 2-aminoethylmethanethiosulphonate (MTSEA) on currents through wild-type human K(v)1.3 (hK(v)1.3) and three mutant channels, hK(v)1.3_L418C, hK(v)1.3_T419C and hK(v)1.3_I420C, in the closed, open and inactivated states was investigated by the patch-clamp technique.

Currents through hK(v)1.3_L418C and hK(v)1.3_T419C channels were irreversibly reduced after the external application of MTSEA in the open state but not in the inactivated and closed states. Currents through hK(v)1.3_I420C channels were irreversibly reduced in the open and inactivated states but not in the closed state. In the presence of verapamil, the MTSEA modification of hK(v)1.3_T419C and hK(v)1.3_I420C channels was prevented, while the MTSEA modification of hK(v)1.3_L418C channels was unaffected.

From our experiments, we conclude that the activation gate of all mutant channels must be open for modification by MTSEA and must also be open during inactivation. In addition, the relative movement of the S6 segments that occur during C-type inactivation includes a movement of the side chains of the amino acids at positions 418 and 419 away from the pore lining. Furthermore, the overlapping binding site for MTSEA and verapamil does not include position 418 in hK(v) 1.3 channels.