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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 killings 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 ion-channel 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 find any evidence of a Ca2+ 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.
Insights
Potassium (K+) channels in human natural killer (NK) cells are essential for their killing function. Blocking these K+ channels inhibits NK cell activity against target cells, demonstrating their critical role.
Area of Science:
- Immunology
- Cell Biology
- Ion Channel Physiology
Background:
- Human natural killer (NK) cells eliminate various target cells.
- Ion channels were hypothesized to be involved in NK cell cytotoxicity, but direct evidence was lacking.
- Previous studies suggested a role for potassium (K+) and sodium (Na+) transport in target cells during cytotoxic T lymphocyte killing, a process resembling NK killing.
Purpose of the Study:
- To investigate the presence and function of ion channels in human NK cells and their target cells.
- To determine the role of identified ion channels in the cytotoxic activity of NK cells.
Main Methods:
- Whole-cell patch-clamp technique to identify ion currents in NK cells and target cells (K562, U937).
- Use of specific ion channel blockers (4-aminopyridine, quinidine, verapamil, Cd2+, tetrodotoxin) to assess their effects on ion currents and NK cell killing.
- Standard 51Cr-release assay to quantify NK cell-mediated target cell killing.
Main Results:
- A voltage-dependent potassium (K+) current was identified in human NK cells.
- This K+ current was inhibited by K+ channel blockers (4-aminopyridine, quinidine) and Ca2+ channel blockers (verapamil, Cd2+).
- Inhibition of NK cell K+ currents with these blockers dose-dependently reduced the killing of K562 and U937 target cells.
- Target cells (K562) exhibited a voltage-dependent Na+ current, but its blockade did not affect killing.
- No Ca2+ current was detected in either NK cells or target cells.
Conclusions:
- Potassium (K+) channels are present in human NK cells and play a necessary role in their cytotoxic function.
- The identified K+ channels in NK cells are crucial for the killing process.
- Endogenous ion channel types in target cells do not appear to be a primary factor in target cell susceptibility to NK cell-mediated lysis.