Regulation of Kv1.3 channels in activated human T lymphocytes by Ca ²⁺ -dependent pathways

Activated T lymphoblasts respond more effectively to mitogenic stimuli than resting T cells, partly through differences in Ca ²⁺ signaling, which in turn depend on K ⁺ channel activity. Both Kv1.3 and Ca ²⁺ -activated K ⁺ (SK4) channels are up-regulated in T lymphoblasts. Since Ca ²⁺ - and calmodulin (CaM)-dependent signaling are key pathways in T-cell activation, we investigated their involvement in regulating the Kv1.3 current. Kv1.3 in lymphoblasts was significantly inhibited by elevating internal Ca ²⁺ to the micromolar level. It was also reduced in a Ca ²⁺ -dependent manner by inhibiting CaM with W-7 or calmidazolium. Part of the CaM-dependence is likely through CaM kinase since the current was also inhibited by the antagonist, KN-62, but not by the inactive analogue, KN-04. Kinase inhibition, unlike CaM inhibition, was only effective at physiological temperatures, a difference that implies involvement of more than one mechanism. We demonstrated a biochemical association of Kv1.3 protein in lymphoblasts with the multifunctional type II CaM kinase, but not with calmodulin. Thus, Kv1.3 forms a multi-protein complex with CaM kinase II (which binds to Ca ²⁺ /CaM) and previously identified proteins (e.g., PSD-95, src tyrosine kinase) that position the channel to respond to signaling pathways that are crucial for T-cell activation and proliferation.