Whole-cell currents in macrophages: II. Alveolar macrophages

Area of Science:

• Immunology
• Cell Physiology
• Ion Channel Research

Background:

• Outwardly rectifying K+ conductance is known in murine macrophages but is rare in human monocyte-derived macrophages (HMDMs).
• Human alveolar macrophages (HAMs) are a primary immune cell population in the lung and a readily available source of human tissue macrophages.

Purpose of the Study:

• To compare the expression of an inactivating outward potassium current (IA) between in vitro differentiated HMDMs and ex vivo isolated HAMs.
• To characterize the properties of IA in both macrophage types.

Main Methods:

• Whole-cell patch-clamp recordings were performed on HMDMs cultured for various durations and on HAMs obtained from bronchoalveolar lavage.
• Ionic currents were analyzed for voltage dependence, ion selectivity, and sensitivity to 4-aminopyridine (4-AP).

Main Results:

• IA was observed in only 5% of HMDMs (49/974 cells) but in 50% of HAMs (160/26 donors).
• The IA current in both cell types was K+ selective, 4-AP sensitive, and showed weakly voltage-dependent inactivation with a recovery time constant of ~30 sec.
• Current inactivation kinetics were dependent on external K+ concentration, and activation/inactivation occurred at specific voltage potentials.

Conclusions:

• HAMs exhibit a significantly higher frequency of IA expression compared to HMDMs.
• The presence of IA may influence mononuclear phagocyte functions such as chemotaxis, phagocytosis, and tumoricidal activity.