State‐dependent blocking mechanism of Kv1.3 channels by the antimycobacterial drug clofazimine

Background and PurposeK(v)1.3 potassium channels are promising pharmaceutical targets for treating immune diseases as they modulate Ca2+ signalling in T cells by regulating the membrane potential and with it the driving force for Ca2+ influx. The antimycobacterial drug clofazimine has been demonstrated to attenuate antigen-induced Ca2+ oscillations, suppress cytokine release and prevent skin graft rejection by inhibiting K(v)1.3 channels with high potency and selectivity. Experimental ApproachWe used patch-clamp methodology to investigate clofazimine's mechanism of action in K(v)1.3 channels expressed in HEK293 cells. Key ResultsClofazimine blocked K(v)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. K(v)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 ImplicationsGiven the prominent role of K(v)1.3 in shaping Ca2+ oscillations, the use-dependent and state-dependent block of K(v)1.3 channels by clofazimine offers therapeutic potential for selective immunosuppression in the context of autoimmune diseases in which K(v)1.3-expressing T cells play a significant role.