Patch-clamp studies in human macrophages: single-channel and whole-cell characterization of two K+ conductances

Human peripheral blood monocytes cultured for varying periods of time were studied using whole-cell and single-channel patch-clamp recording techniques. Whole-cell recordings revealed both an outward K current activating at potentials greater than 20 mV and an inwardly rectifying K current present at potentials negative to -60 mV. Tail currents elicited by voltage steps that activated outward current reversed near EK, indicating that the outward current was due to a K conductance. The I-V curve for the macroscopic outward current was similar to the mean single-channel I-V curve for the large conductance (240 pS in symmetrical K) calcium-activated K channel present in these cells. TEA and charybdotoxin blocked the whole-cell outward current and the single-channel current. Excised and cell-attached single-channel data showed that calcium-activated K channels were absent in freshly isolated monocytes but were present in greater than 85% of patches from macrophages cultured for greater than 7 days. Only 35% of the human macrophages cultured for greater than 7 days exhibited whole-cell inward currents. The inward current was blocked by external barium and increased when [K]o increased. Inward-rectifying single-channel currents with a conductance of 28 pS were present in cells exhibiting inward whole-cell currents. These single-channel currents are similar to those described in detail in J774.1 cells (L.C. McKinney & E.K. Gallin, J. Membrane Biol. 103:41-53, 1988).