The cumulative number of publications as of November 2003 on (a) ‘lymphocytes and K⁺ channels’ and (b) ‘K⁺ channels and proliferation’. Key discoveries in both fields are highlighted. Abbreviations: CaM, calmodulin; ChTX, charybdotoxin; EAE, experimental autoimmune encephalomyelitis; EAG, ether a-go-go; IKCa1, intermediate-conductance Ca²⁺ -activated K⁺ channel subtype 1; HERG, human ether-à-go-go-related gene; Kv1.3^high, high levels of Kv1.3 channels; MgTX, margatoxin; MS, multiple sclerosis; ShK, Stichodactyla helianthus toxin; T_EM cells, effector memory T cells. (Data are from [1–6,8,9,11,14,16,30,32,35,36,46,51,54,56,58,59,64–81].)

(a) Backbone structures of charybdotoxin (ChTX), Stichodactyla helianthus toxin (ShK) and maurotoxin (MTX), which are peptide inhibitors of voltage-dependent Kv1.3 channels and intermediate-conductance Ca²⁺ -activated IKCa1 channels. The crucial lysine that occludes the channel pore is highlighted in red in each structure: Lys27 in ChTX; Lys22 in ShK; and Lys23 in MTX. The disulfide bonds are highlighted in yellow. Arg1 in ShK, to which the fluorophore fluorescein-6-carboxylic acid (F6CA) is attached, is highlighted in white. Such fluorophores attached to specific inhibitors can be used to visualize these K⁺ channels. (b,c) Plots of potency versus year of publication for peptide (red; triangles) and small-molecule (blue; squares) blockers of Kv1.3 (b) and IKCa1 (c) channels in lymphocytes are shown. Abbreviations: AgTX2, agio-toxin-2; 4-AP, 4-aminopyridine; ChTX-K32E, charybdotoxin derivative with glutamate at position 32 in place of the native lysine; HsTX1, Heterometrus spinnifer toxin 1; KTX, kaliotoxin; MgTX, margatoxin; NTX, noxiustoxin; PAC, 4-phenyl-4-[3-(2-methoxyphenyl)-3-oxo-2-azaprop-1-yl]cyclohexanone; Pi2, Pandinus imperator toxin 2; ShK–Dap22, Stichodactyla helianthus toxin with diaminopropionic acid introduced at position 22 in place of the native lysine; TEA, tetraethylammonium chloride. See Chemical names. (Data are from [2,5–7,10–13,32,33,35,38,42,43,45–47,49,51,52,55,58,82].)

(a) Schematic showing the average numbers of Kv1.3 channels and IKCa1 channels per cell in naïve (CCR7⁺ CD45RA⁺ ), central memory (T_CM) (CCR7⁺ CD45RA⁻) and effector memory (T_EM) (CCR7⁻CD45RA⁻) cells. Naïve and T_CM cells increase IKCa1 channel expression following activation, whereas T_EM cells increase Kv1.3 channel expression. (b) Plot of Kv1.3 channel numbers per cell determined by whole-cell patch-clamp in different T-cell populations versus difference (D) values of Stichodactyla helianthus toxin (ShK)–fluorescein-6-carboxylic acid (F6CA) staining obtained by flow cytometry; these data were obtained from [40]. The D value is a measure of the difference in fluorescence intensity between ShK–F6CA-stained cells and background fluorescence from unstained cells of the same population. Abbreviation: TCR, T-cell receptor.

The involvement of voltage-dependent Kv1.3 channels, intermediate-conductance Ca²⁺ -activated IKCa1 channels and voltage-independent Ca²⁺ release-activated Ca²⁺ (CRAC) channels in the activation of a CD4⁺ T cells by an antigen-presenting cell (APC) is shown. Engagement of the T-cell receptor–CD3 complex through an antigenic peptide presented in the context of major histocompatibility complex (MHC) class II activates phospholipase C (PLC), which leads to the activation of protein kinase C (PKC) and the production of inositol (1,4,5)-trisphosphate [Ins(1,4,5) P₃], which liberates Ca²⁺ from intracellular stores. Simultaneous activation of CD28 by the co-stimulatory molecules CD80 or CD86 further amplifies the resulting Ca²⁺ signal. The rise in the intracellular concentration of Ca²⁺ activates the phosphatase calcineurin, which then dephosphorylates the transcription factor nuclear factor of activated T cells (NFAT), enabling it to accumulate in the nucleus and bind to the promoter of the gene encoding interleukin 2 (IL-2). Parallel activation of the c-JUN N-terminal kinase (JNK) and Ras by PKC results in the activation of other transcription factors and initiates transcription of various genes and finally T-cell proliferation. CRAC, Kv1.3 and IKCa1 channels regulate Ca²⁺ signaling. Depletion of internal Ca²⁺ stores causes CRAC channels in the membrane to open, and the ensuing Ca²⁺ influx sustains elevated levels of cytosolic Ca²⁺. Ca²⁺ influx through CRAC channels is reduced following membrane depolarization. The driving force for Ca²⁺ entry is restored by membrane hyperpolarization brought about by the opening of Kv1.3 channels in response to membrane depolarization and the opening of IKCa1 channels as a consequence of elevated concentrations of cytosolic Ca²⁺. Selective blockade of K⁺ channels leads to membrane depolarization, inhibits Ca²⁺ influx and shuts down cytokine production and cell proliferation. Abbreviations: CaM, calmodulin; hDlg, human homolog of the Drosophila discs large tumor suppressor protein; VCAM-4, vascular cell adhesion molecule 4; ZIP-1, Zrt/Irt-like protein.

Structures of small-molecule Kv1.3 channel and IKCa1 channel blockers. See Tables 1 and 2 for their K_d values on the respective channels.