A variety of stimuli, including cytokines and adhesion to surfaces and matrix proteins, can regulate macrophage function, in part through changes in Ca2+-dependent second messengers. While fluctuation in in-tracellular Ca2+ is an important modulator of cellular activation, little attention has been paid to the roles of other ions whose cytoplasmic concentrations can be rapidly regulated by ion channels. To examine the role of ion channels in macrophage function, we undertook patch clamp studies of human culture-derived macrophages grown under serum-free conditions. The major ionic current in these cells was carried by an outwardly rectifying K+ channel, which had a single-channel conductance of 229 pS in symmetrical K+-rich solution and macroscopic whole-cell conductance of 9.8 nS. These channels opened infrequently in resting cells but were activated immediately by (i) adhesion of mobile cells onto a substrate, (ii) stretch applied to isolated membrane patches in Ca2+-free buffers, (iii) intracellular Ca2+ (EC50 of 0.4 μm), and (iv) the cytokine IL-2. Furthermore, barium and 4-aminopyridine, blockers of this channel, altered the organization and structure of the cytoskeletal proteins actin, tubulin and vimentin. These cytoskeletal changes were associated with reversible alteration to the morphology of the cells. Thus, we have identified an outwardly rectifying K+ channel that appeared to be involved in cytokine and adherence-mediated macrophage activation, and in the maintenance of cytoskeletal integrity and cell shape.
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We thank Ken Wyse and Sue Bennett for excellent technical assistance. This work was supported by the National Health & Medical Research Council of Australia, the National Heart Foundation of Australia, the Clive & Vera Ramaciotti Foundation of Australia, the St Vincent's Hospital Clinic Foundation and a St Vincent's Hospital Research Grant.
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Martin, D.K., Bootcov, M.R., Campbell, T.J. et al. Human macrophages contain a stretch-sensitive potassium channel that is activated by adherence and cytokines. J. Membarin Biol. 147, 305–315 (1995). https://doi.org/10.1007/BF00234528
- Potassium channel
- Patch clamp