[Properties of the GM-CSF-induced outward K+ current in murine peritoneal exudate macrophages]

Whole-cell patch-clamp technique was used to study the changes of ionic currents in murine peritoneal exudate macrophages (PEMs) prestimulated with granulocyte-macrophage colony-stimulating factor (GM-CSF, 16 ng/ml) for periods from 0.5 up to 6 d. The GM-CSF-treated PEMs developed a GM-CSF-induced transient inactivating outward K+ current (IA). IA showed steady-state inactivation over the physiological voltage range and possessed frequency dependence of inactivation when depolarizing pulses were applied at a frequency of 0.5 Hz. IA was selectively inhibited by extracellular 4-AP (3 mmol/L). When [Ca2+]i was increased (from pCa 8 to 6), the amplitudes of IA were depressed significantly. When the PEMs were exposed to cycloheximide (0.3 microgram/ml), a protein synthesis inhibitor, for 12 h, IA expression was completely suppressed. It was notable that the changes of the current expression, activation behavior and kinetic properties occurred during GM-CSF treatment. When PEMs were pretreated for a 2-d period, the frequency of IA expression reached a peak value (55% in a total of 27 cells), PEMs exhibited the highest density of the corresponding channel proteins, half-maximal activation of IA was most easily achieved with a value of -27.55 mV, and the time course of activation and inactivation during depolarization proceeded rapidly. However, along with continuous incubation with GM-CSF, the number of PEMs expressing IA decreased, the channel proteins were down regulated constantly, the activation curve for IA shifted to positive potentials, and the activation time and inactivation time of IA slowed down. These results indicated that GM-CSF could induce a transient inactivating outward K+ current in PEMs, which may have a close relation to the state of functional activation of macrophages primed with GM-CSF.