Fig. 3. Anandamide directly blocks TASK-1 independently of the CB1/CB2 cannabinoid receptors. (A) Effects of the CB1 receptor antagonist SR141716A, at a concentration of 10 µM, on TASK-1 inhibition induced by 3 µM WIN552122 and 3 µM methanandamide. (B) Effects of 10 µM anandamide on a C-terminally truncated mutant of TASK-1 (TA248 deleted at His280) lacking all phosphorylation sites. Current densities measured at 0 mV in a physiological K⁺ gradient are 8.4 ± 1.1 pA/pF (n = 15) for ΔCt TASK-1 and 16.9 ± 0.8 pA/pF (n = 119) for TASK-1 WT. (C) Effects of 10 µM anandamide and external acidosis to pH 6.4 on the mutant TASK-1 ΔCt. (D) 3 µM methanandamide produces a similar block of TASK-1 expressed in COS, CHO and HEK transfected cells. TASK-1 currents are measured at 0 mV. The holding potential is –80 mV and cells are stimulated with voltage ramps of 800 ms duration, from –130 mV up to 100 mV. (E) Effects of 3 µM methanandamide (met) on an outside-out patch expressing TASK-1. The holding potential is –80 mV and the external medium contains 155 mM K⁺. (F) Effects of 3 µM methanandamide (met) on an outside-out patch expressing a chimera between the core of TASK-1 and the entire C-terminal region of TREK-1 (TA242/TR293). The holding potential is –80 mV and cells are stimulated with voltage ramps of 800 ms duration, from –130 mV up to 100 mV. Currents are recorded in a physiological K⁺ gradient and the intracellular medium contains 1 mM GDP-βs.