Potassium channels mediate killing by human natural killer cells.

Abstract

Human natural killer (NK) cells in peripheral blood spontaneously recognize and kill a wide variety of target cells. It has been suggested that ion channels are involved in the killing process because there is a Ca-dependent stage and because killing by presensitized cytotoxic T lymphocytes, which in many respects resembles NK killing, is associated with changes in K and Na transport in the target cell. However, no direct evidence exists for ion channels in NK cells or in their target cells. Using the whole-cell variation of the patch-clamp technique, we found a voltage-dependent potassium (K+) current in NK cells. The K+ current was reduced in a dose-dependent manner by the K-channel blockers 4-aminopyridine and quinidine and by the traditional Ca-channel blockers verapamil and Cd2 . We tested the effects of ionchannel blockers on killing of two commonly used target cell lines: K562, which is derived from a human myeloid leukemia, and U937, which is derived from a human histiocytic leukemia.Killing of K562 target cells, determined in a standard 51Cr-release assay, was inhibited in a dose-dependent manner by verapamil, quinidine, Cd2+, and 4-aminopyridine at concentrations comparable to those that blocked the K+ current in NK cells. In K562 target cells only a voltage-dependent Na' current was found and it was blocked by concentrations of tetrodotoxin that had no effect on killing. Killing of U937 target cells was also inhibited by the two ion-channel blockers tested, quinidine and verapamil. In this cell line only a small K+ current was found that was similar to the one in NK cells. We could not rind any evidence of a Ca21 current in target cells or in NK cells; therefore, our results cannot explain the Ca dependence of killing. Our findings show that there are K channels in NK cells and that these channels play a necessary role in the killing process. In contrast, the endogenous channel type in the target cell is probably not a factor in determining target cell sensitivity to natural killing.

Kv1.3 potassium channels are localized in the immunological synapse formed between cytotoxic and target cells

“…Based on biophysical and pharmacological characterization of the voltage-gated K ϩ current, we reported in this study that activated CTLs generated by using our experimental procedures expressed Kv1.3 channels in their plasma membrane. This result agrees with previous studies (13,45,46) where a voltage-gated potassium conductance was found in human cytotoxic T cells, in alloantigen-stimulated T cells, in CD8 ϩ T effector memory cells, and in NK cells. Thus, transfection of Kv1.3͞FLAG channels into CTLs leads to the expression of a native-like channel.…”

“…The major physiological function of Kv1.3 channels is the control of the membrane potential of T cells (47). It has been shown earlier (12)(13)(14), as well as in this paper, that potassium channel blockers inhibit the cytotoxic activity of CTLs. CTL- mediated cytotoxicity is also regulated by membrane potential (16); however, we do not think that recruitment of Kv1.3 channels into the IS might result in a significantly different local membrane potential, as compared to the rest of the cell.…”

“…It is generally accepted that membrane potential and the activity of potassium channels is important for generation and propagation of the mitogenic signal in lymphocytes (40), for cell volume regulation (41), and for cell-mediated cytotoxicity (12,13). Previous studies (42,43) reported a wide variety of voltagegated ion channels in the plasma membrane of human and rodent T lymphocytes.…”

“…Activity of voltage-gated potassium channels has been shown to modulate the killing process mediated by both NK cells and CTLs (12)(13)(14). Blockers of voltage-gated potassium channels inhibit NK-and CTL-mediated cytotoxicity in doses comparable to those required to block ionic currents.…”

Ion channels and anti-cancer immunity

“…The presence of Nav1.7 seems to depolarize the membrane potential of immature dendritic cells and stimulate cell migration, whereas pharmacological inhibition of Nav1.7 by TTX sensitized the immature dendritic cells for activation signals [43]. NK lymphocytes that play important roles in the control of tumours and viral infections express K þ channels identified as Kv1.3 and KCa3.1 [44,45]. Interestingly, as found with T and B lymphocytes (see below), the relative numbers of Kv1.3 and KCa3.1 vary between subpopulations of NK cells and confer different sensitivities to selective blockers of these channels [45].…”