Anesthetic-like interaction of the sleep-inducing lipid oleamide with voltage-gated sodium channels in mammalian brain

Abstract

Background: cis-9,10-Octadecenoamide (cOA) accumulates in cerebrospinal fluid during sleep deprivation and induces sleep in animals, but its cellular actions are poorly characterized. In earlier studies, like a variety of anesthetics, cOA modulated γ-aminobutyric acidA receptors and inhibited transmitter release/burst firing in cultured neurones or synaptoneurosomes. Methods: Here, radioligand binding ([3H]batrachotoxinin A 20-α-benzoate and mouse central nervous system synaptoneurosomes) and voltage clamp (whole cell recording from cultured NIE115 murine neuroblastoma) confirmed an interaction with neuronal voltage-gated sodium channels (VGSC). Results: cOA stereoselectively inhibited specific binding of toxin to VGSC (inhibitor concentration that displaces 50% of specifically bound radioligand, 39.5 μM). cOA increased (4×) the Kd of toxin binding without affecting its binding maximum. Rate of dissociation of radioligand was increased without altering association kinetics, suggesting an allosteric effect (indirect competition at site 2 on VGSC). cOA blocked tetrodotoxin-sensitive sodium currents (maximal effect and affinity were significantly greater at depolarized potentials; P < 0.01). Between 3.2 and 64 μM, the block was concentration-dependent and saturable, but cOA did not alter the V50 for activation curves or the measured reversal potential (P > 0.05). Inactivation curves were significantly shifted in the hyperpolarizing direction by cOA (maximum, -15.4 ± 0.9 mV at 32 μM). cOA (10 μM) slowed recovery from inactivation, with τ increasing from 3.7 ± 0.4 ms to 6.4 ± 0.5 ms (P < 0.001). cOA did not produce frequency-dependent facilitation of block (up to 10 Hz). Conclusions: These effects (and the capacity of oleamide to modulate γ-aminobutyric acidA receptors in earlier studies) are strikingly similar to those of a variety of anesthetics. Oleamide may represent an endogenous ligand for depressant drug sites in mammalian brain.