Whole-cell patch clamp recordings were used to investigate the properties of a non-inactivating outward current observed in mouse cerebellar Purkinje neurones at a holding potential of −20 mV. Increasing the external potassium (K+) concentration from 3 mM to 20 mM produced a rightward shift in the observed reversal potential of ∼30 mV or ∼40 mV for a K+-or a caesium (Cs+)-based intracellular solution respectively, indicating the outward current was a K+ current. The outward current was partially inhibited by the K+ channel blocker, tetraethylammonium (TEA; IC50=0.15 mM). Subsequently, the background or TEA-insensitive current was measured in the presence of 1 mM TEA. The background current was reversibly inhibited by barium (Ba2+; 300 μM, 50%) and potentiated by the application of arachidonic acid (AA; 1 mM, 62%). The volatile anaesthetic, halothane (1 mM), and the neuroprotectant, riluzole (500 μM), both reversibly inhibited the background current by 54% and 36% respectively. The background current was insensitive to changes in both intracellular and extracellular acidification. The GABAB and μ-opioid receptor agonists, baclofen and [D-Ala2, N-MePhe4-Gly-ol5] enkephalin (DAMGO) both reversibly potentiated the outward current by 42% and 26% respectively. In contrast, the metabotropic glutamate receptor and acetylcholine receptor agonists, (S)-3,5-dihydroxyphenylglycine (DHPG) and muscarine both reversibly inhibited the outward current by 48% and 42% respectively. These data suggest that cerebellar Purkinje neurones possess a background current which shares several properties with recently cloned two-pore K+ channels, particularly THIK-1. |