Pharmacological characterization of a non-inactivating outward current observed in mouse cerebellar Purkinje neurones

1 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. 2 Increasing the external potassium (K) concentration from 3 mm to 20 mm produced a rightward shift in the observed reversal potential of similar to30 mV or similar to40 mV for a K+-or a caesium (Cs+)-based intracellular solution respectively, indicating the outward current was a K+ current. 3 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 I mm TEA. 4 The background current was reversibly inhibited by barium (Ba2+; 300 muM, 50%) and potentiated by the application of arachidonic acid (AA; 1 mM, 62%). 5 The volatile anaesthetic, halothane (1 mM), and the neuroprotectant, riluzole (500 muM), both reversibly inhibited the background current by 54% and 36% respectively. 6 The background current was insensitive to changes in both intracellular and extracellular acidification. 7 The GABA(B) and mu-opioid receptor agonists, baclofen and [D-Ala(2), N-MePhe(4)-Gly-ol(5)] 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. 8 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.