VOLTAGE-GATED POTASSIUM CHANNELS REGULATE CALCIUM-DEPENDENT PATHWAYS INVOLVED IN HUMAN LYMPHOCYTE-T ACTIVATION

The role that potassium channels play in human T lymphocyte activation has been investigated by using specific potassium channel probes. Charybdotoxin (ChTX), a blocker of small conductance Ca2+-activated potassium channels (P(K,Ca)) and voltage-gated potassium channels (P(K,V)) that are present in human T cells, inhibits the activation of these cells. ChTX blocks T cell activation induced by signals (e.g., anti-CD2, anti-CD3, ionomycin) that elicit a rise in intracellular calcium ([Ca2+]i) by preventing the elevation of [Ca2+]i in a dose-dependent manner. However, ChTX has no effect on the activation pathways (e.g., anti-CD28, interleukin 2 [IL-2]) that are independent of a rise in [Ca2+]i. In the former case, both proliferative response and lymphokine production (IL-2 and interferon gamma) are inhibited by ChTX. The inhibitory effect of ChTX can be demonstrated when added simultaneously, or up to 4 h after the addition of the stimulants. Since ChTX inhibits both P(K,Ca) and P(K,V), we investigated which channel is responsible for these immunosuppressive effects with the use of two other peptides, noxiustoxin (NxTX) and margatoxin (MgTX), which are specific for P(K,V). Theses studies demonstrate that, similar to ChTX, both NxTX and MgTX inhibit lymphokine production and the rise in [Ca2+]i. Taken together, these data provide evidence that blockade of P(K,V) affects the Ca2+-dependent pathways involved in T lymphocyte proliferation and lymphokine production by diminishing the rise in [Ca2+]i that occurs upon T cell activation.