Microglial cells are the major immuno-competent cells in the mammalian brain where they play a crucial role in maintaining the CNS environment in the face of various potentially pathological insults. We have used electrophysiological and pharmacological methods to study a microglial cell line (C13-NJ) derived from the human CNS. In whole-cell patch clamp experiments we identified an inward current that exhibited biophysical hallmarks of a classical voltage-gated Na(+) channel. This identification was confirmed by further experiments in which the current was eliminated by removal of Na(+) from the bathing medium. Relatively weak inhibition by TTX (30+/-3% at 500nM) and sensitivity to 100microM Zn(2+) suggested that this current was predominantly mediated by the cardiac sodium channel isoform Na(V)1.5. Sodium current density was not altered by treatment with either lipopolysaccharide or beta-amyloid 1-42. The presence of the Na(V)1.5 subunit in microglial cells is discussed with respect to its reported roles in phagocytosis, proliferation and migration of other non-cardiac cells.