Membrane hyperpolarizations and ionic channels in cultured human monocytes

Until recently, studies on the resting electrophysiological properties of mononuclear phagocytes were done with intracellular microelectrodes. These cells were found to have generally low resting membrane potentials (range −10 to −30 mV) and to show single and oscillatory hyperpolarizations (1–4). Measurements in cells with high resting membrane potentials have shown, however, that some mononuclear phagocytes can have electrically excitable membranes (5, 6). Whether these measurements are characteristic of a subpopulation of mononuclear phagocytes or reflect the limitations of the techniques used for measurements remains uncertain (7). Hyperpolarizing responses in mononuclear phagocytes are known to be due to an increase in the conductance of the membrane for K+ evoked by an increase in intracellular Ca2+ (4, 8, 9). This K+(Ca2+) conductance is also present in L cells (10–13). The hyperpolarizing response (HR) has been extensively investigated in L cells and has been implicated with such cellular functions as phagocytosis (14), pinocytosis (15) and cell motility (16). In macrophages the HR has been found to be involved in chemotaxis (17) and possibly also phagocytosis (18).