The aim of these studies was to identify the voltage-gated potassium channels in human alveolar macrophages and investigate the potential physiological role. Macrophages were obtained from macroscopically normal lung tissue derived from surgical resections, isolated by adherence and identified by morphology. Patients consented to this use of tissue. Whole-cell recordings from cells days 1 to 3 in culture were used to study Kv channel currents. The pipette solution contained (mM): 150 KCl, 10 Hepes and 10 EGTA (pH 7.2) and superfused with saline containing 145 NaCl, 5 KCl, 10 Hepes, 12 glucose, 1 MgCl₂ and 2 CaCl₂ (pH 7.3). From a holding potential of -100 mV, depolarising pulses activated an outward current, underlying conductance was fitted by a Boltzmann function; V_1/2 = -18 ± 0.8 mV and k = 9.4 ± 0.75 mV (means ± S.E.M., n = 5). Tail currents reversed around the theoretical value for E_K (extracellular potassium 5 mM, 20 mM and 150 mM) demonstrating a potassium-selective conductance. Margatoxin blocked this outward current with IC₅₀ 162 ± 11 pM (n = 5), consistent with Kv1.3 (Bednarek et al. 1994).

For identification of Kv channel mRNA transcripts, a pure macrophage population was isolated from contaminating myofibroblasts. Macrophages were identified by phagocytosis of BODIPY-labelled, IgG coated zymosan and sorted by flow cytometry. Reverse transcription-polymerase chain reaction (RT-PCR) was performed to detect the transcripts for Kv1.1, Kv1.2, Kv1.3, Kv1.4, Kv1.5, Kv1.6, Kv2.1, Kv2.2, Kv2.3, Kv3.1, Kv3.3, Kv3.4, Kv4.1, Kv4.2 and Kv4.3 channels, only Kv1.3 channel primer pairs gave a product of expected size (269 base pairs).

We sought to determine whether Kv1.3 channels played a role in phagocytosis. In current-clamp recordings, resting membrane potential was -34 ± 1.1 mV (n = 7). Exposure to 1 nM margatoxin depolarised the membrane to -4.6 ± 1.1 mV (n = 5), suggesting that Kv1.3 channels are involved in setting the resting membrane potential. However, phagocytosis was unaffected; the percentage of cells sorted as macrophages from the total cell population by flow cytometry was 37 ± 7.6 % (n = 3) and 35 ± 8.3 % (n = 3) for control cells and in the presence of 1 nM margatoxin, respectively. This indicates that functioning Kv1.3 channels are not required for Fc receptor-mediated phagocytosis.

All procedures accord with current local guidelines and the Declaration of Helsinki.