anandamide and Acidosis

Oxygen depletion (O(2)) and a decrease in pH are initial pathophysiological events in stroke development, but secondary mechanisms of ischemic cell death are incompletely understood. By patch-clamp recordings of brain slice preparations we show that TASK1 and TASK3 channels are inhibited by pH-reduction (42+/-2%) and O(2) deprivation (36+/-5%) leading to membrane depolarization, increased input resistance and a switch in action potential generation under ischemic conditions. In vivo TASK blockade by anandamide significantly increased infarct volumes at 24 h in mice undergoing 30 min of transient middle cerebral artery occlusion (tMCAO). Moreover, blockade of TASK channels accelerated stroke development. Supporting these findings TASK1(-/-) mice developed significantly larger infarct volumes after tMCAO accompanied by worse outcome in functional neurological tests compared to wild type mice. In conclusion, our data provide evidence for an important role of functional TASK channels in limiting tissue damage during cerebral ischemia.

Topics: Acidosis; Animals; Arachidonic Acids; Brain; Brain Ischemia; Endocannabinoids; Hypoxia, Brain; In Vitro Techniques; Infarction, Middle Cerebral Artery; Male; Membrane Potentials; Mice; Mice, Inbred C57BL; Mice, Knockout; Nerve Tissue Proteins; Neurons; Polyunsaturated Alkamides; Potassium Channels; Potassium Channels, Tandem Pore Domain; Receptor, Cannabinoid, CB1; Receptor, Cannabinoid, CB2; RNA, Messenger; Stroke; Thalamus; TRPV Cation Channels

The mechanisms underlying neuronal excitotoxicity during hypoxic/ischemic episodes are not fully understood. One feature of such insults is a rapid and transient depolarization of central neurons. TASK-1, an open rectifying K+ leak channel, is significant in setting the resting membrane potential of rat cerebellar granule neurons by mediating a standing outward K+ current. In this study we investigate the theory that the transient neuronal depolarization seen during hypoxia is due to the inhibition of TASK-1.. Activity of TASK-1 in primary cultures of rat cerebellar granule neurons was investigated by the whole-cell patch-clamp technique. Discriminating pharmacological and electrophysiological maneuvers were used to isolate the specific channel types underlying acute hypoxic depolarizations.. Exposure of cells to acute hypoxia resulted in a reversible and highly reproducible mean membrane depolarization of 14.2+/-2.6 mV (n=5; P<0.01). Two recognized means of inhibiting TASK-1 (decreasing extracellular pH to 6.4 or exposure to the TASK-1-selective inhibitor anandamide) abolished both the hypoxic depolarization and the hypoxic depression of a standing outward current, identifying TASK-1 as the channel mediating this effect.. Our data provide compelling evidence that hypoxia depolarizes central neurons by specific inhibition of TASK-1. Since this hypoxic depolarization may be an early, contributory factor in the response of central neurons to hypoxic/ischemic episodes, TASK-1 may provide a potential therapeutic target in the treatment of stroke.

Topics: Acidosis; Animals; Arachidonic Acids; Cell Hypoxia; Cells, Cultured; Endocannabinoids; Hydrogen-Ion Concentration; Membrane Potentials; Nerve Tissue Proteins; Neurons; Patch-Clamp Techniques; Polyunsaturated Alkamides; Potassium; Potassium Channel Blockers; Potassium Channels; Potassium Channels, Tandem Pore Domain; Rats