Identification of a region in the TASK3 two pore domain potassium channel that is critical for its blockade by methanandamide.
OBJECTIVE
The TASK subfamily of two pore domain potassium channels (K2P) encodes for leak K currents, contributing to the resting membrane potential of many neurons and regulating their excitability. TASK1 and TASK3 channels are regulated by a number of pharmacological and physiological mediators including cannabinoids such as methanandamide. In this study, we investigate how methanandamide blocks these channels.


METHODS
Currents through wild type and mutated TASK1 and TASK3 channels expressed in modified HEK-293 cells were measured using whole-cell electrophysiological recordings in the presence and absence of methanandamide.


RESULTS
Methanandamide (3 microM) produced substantial block of hTASK1, hTASK3 and mTASK3 channels but was most potent at blocking hTASK3 channels. Block of these channels was irreversible unless cells were washed with buffer containing bovine serum albumin. Mutation of the distal six amino acids of TASK1 did not alter methanandamide inhibition, whilst C terminal truncation of TASK3 channels caused a small but significant reduction of inhibition. However, deletion of six amino acids (VLRFLT) at the interface between the final transmembrane domain and cytoplasmic C terminus of TASK3 channels gave functional currents that were no longer inhibited by methanandamide or by activation of GPCRs.


CONCLUSIONS
Methanandamide potently blocked TASK3 and TASK1 channels and both methanandamide and G protein-mediated inhibition converged on the same intracellular gating pathway. Physiologically, methanandamide block of TASK1 and TASK3 channels may underpin a number of CNS effects of cannabinoids that are not mediated through activation of CB1 or CB2 receptors.
Veale
E L
EL
Medway School of Pharmacy, Universities of Kent and Greenwich at Medway, Kent, UK.
Buswell
R
R
Clarke
C E
CE
Mathie
A
A
D000596:Amino Acids / Q000235:genetics; D000818:Animals; D001095:Arachidonic Acids / Q000494:pharmacology*; D001665:Binding Sites / Q000235:genetics; D002417:Cattle; D002460:Cell Line; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D016297:Mutagenesis, Site-Directed / Q000379:methods; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology; D018408:Patch-Clamp Techniques; D010766:Phosphorylation / Q000187:drug effects; D024683:Potassium Channels, Tandem Pore Domain / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000502:physiology*; D011493:Protein Kinase C / Q000378:metabolism; D043587:Receptor, Muscarinic M3 / Q000235:genetics / Q000502:physiology; D043562:Receptors, G-Protein-Coupled / Q000235:genetics / Q000502:physiology; D012710:Serum Albumin, Bovine / Q000494:pharmacology; D015032:Zinc / Q000494:pharmacology