Acetylcholine reduces inward rectification on thymus-derived macrophage cells in culture

Cultures prepared from dissociated rat thymus were examined 1-2 weeks after plating. Macrophage cells were identified by their adherence, morphological appearance, and ability to phagocytize carbon particles or heat-inactivated Staphylococcus aureus. Whole cell current recordings from macrophage cells revealed an inward current at potentials more negative than the equilibrium potential for potassium and an outward current at potentials more positive than -40 mV in normal recording solution. Acetylcholine or muscarine caused a reduction in inward current but did not alter the outward current. The inward current and acetylcholine effect were seen at less negative potentials by decreasing the potassium equilibrium potential and both were blocked by the addition of cesium to the external recording solution. These results indicated that the inward current was mediated by potassium through the inward or anomalous rectifier. Physiologically, the action of acetylcholine on the inward rectifier of these macrophage cells may be mediated by cholinergic innervation of the thymus.