State-dependent blocking mechanism of Kv 1.3 channels by the antimycobacterial drug clofazimine.

background and purposeKv 1.3 potassium channels are promising pharmaceutical targets for treating immune diseases as they modulate Ca(2+) signalling in T cells by regulating the membrane potential and with it the driving force for Ca(2+) influx. The antimycobacterial drug clofazimine has been demonstrated to attenuate antigen-induced Ca(2+) oscillations, suppress cytokine release and prevent skin graft rejection by inhibiting Kv 1.3 channels with high potency and selectivity. EXPERIMENTAL APPROACH: We used patch-clamp methodology to investigate clofazimine's mechanism of action in Kv 1.3 channels expressed in HEK293 cells. KEY

resultsClofazimine blocked Kv 1.3 channels by involving two discrete mechanisms, both of which contribute to effective suppression of channels: (i) a use-dependent open-channel block during long depolarizations, resulting in accelerated K(+) current inactivation and (ii) a block of closed deactivated channels after channels were opened by brief depolarizations. Both modes of block were use-dependent and state-dependent in that they clearly required prior channel opening. The clofazimine-sensitive closed-deactivated state of the channel was distinct from the resting closed state because channels at hyperpolarized voltages were not inhibited by clofazimine. Neither were channels in the C-type inactivated state significantly affected. Kv 1.3 channels carrying the H399T mutation and lacking C-type inactivation were insensitive to clofazimine block of the closed-deactivated state, but retained their susceptibility to open-channel block. CONCLUSIONS AND IMPLICATIONS: Given the prominent role of Kv 1.3 in shaping Ca(2+) oscillations, the use-dependent and state-dependent block of Kv 1.3 channels by clofazimine offers therapeutic potential for selective immunosuppression in the context of autoimmune diseases in which Kv 1.3-expressing T cells play a significant role.