Evidence for both a calcium-activated potassium conductance and an inward rectifying potassium conductance in macrophages

Abstract

In recent years it has become evident that many cells of nonneuronal origin, including the macrophage, exhibit voltage-dependent conductance previously associated with excitable cells (1, 2). However, because the field of macrophage electrophysiology is relatively new, many questions remain unanswered that pertain to the specific conductances found in these cells and their role in cell function. At present it is known that macrophages exhibit a calcium-activated potassium conductance (3, 4), an inward rectifying potassium conductance (5), and a delayed potassium conductance (6, 7). Spiking behavior, implicating the presence of another voltage-dependent conductance (2), and an electrogenic sodium-potassium pump (8) also have been reported in macrophages. Unfortunately, progress has been hampered by the fact that macrophages are very sensitive to microelectrode-induced damage. Patch clamping substantially reduces penetrationinduced damage and thus has enabled considerable progress to be made in the field of macrophage electrophysiology (1, 4, 6). We have used this technique to confirm and extend some of the observations we previously made using intracellular microelectrodes. This paper reviews the evidence for the presence of an inward rectifying potassium conductance and a calcium- and voltage-dependent potassium conductance in macrophages, and includes some of our more recent data measuring these conductances with patch-clamp techniques.