Introduction: A mechanism of anesthesia has recently been proposed which predicts that coreleased neurotransmitters may modulate neurotransmitter receptors for which they are not the native agonist in a manner similar to anesthetics.
Methods: We tested this prediction by applying acetylcholine to a NR1/NR2A N-methyl-d-aspartate receptor, glycine to a wild-type alpha(1)beta(2) and anesthetic-resistant alpha(1)(S270I)beta(2) gamma-amino-butyric acid (GABA) type A receptor, and GABA to a homomeric alpha(1) wild type and anesthetic-resistant alpha(1) S267I glycine receptor. Receptors were expressed in Xenopus laevis oocytes and studied using two-electrode voltage clamping.
Results: We found inhibition of N-methyl-d-aspartate receptor function by acetylcholine, enhancement of glycine receptor function by GABA, and enhancement of GABA type A receptor function by glycine. As expected of compounds with anesthetic activity, GABA showed far less potentiation (enhancement) of the function of the anesthetic-resistant S267I glycine receptor than that of the wild-type receptor. Glycine potentiated the function of wild-type GABA type A receptors but inhibited the function of the anesthetic-resistant S270I GABA type A receptor.
Conclusions: These results show that neurotransmitters that are coreleased onto anesthetic-sensitive receptors may modulate the function of receptors for which they are not the native agonist via an anesthetic-like mechanism. These findings lend support to a recent theory of anesthetic action.