AN INHALATIONAL ANESTHETIC BINDING DOMAIN IN THE NICOTINIC ACETYLCHOLINE-RECEPTOR

To determine inhalational anesthetic binding domains on a ligand gated ion channel, I used halothane direct photoaffinity labeling of the ni cotinic acetylcholine receptor (nAChR) in native Torpedo membranes, [C -14]Halothane photoaffinity labeling of both the native Torpedo mem me mbranes and the isolated nAChR was saturable, with K-d values within t he clinically relevant range, All phospholipids were labeled, with gre ater than 95% of the label in the acyl chain region, Electrophoresis o f labeled nAChR demonstrated no significant subunit selectivity for ha lothane incorporation. Within the alpha-subunit, greater than 90% of l abel was found in the endoprotease Glu-C digestion fragments which con tain the four transmembrane regions, and the pattern was different fro m that reported for photoactivatable phospholipid binding to the nAChR , Unlabeled halothane reduced labeling more than did isoflurane, sugge sting differences in the binding domains for inhalational anesthetics in the nAChR. These data suggest multiple similar binding domains for halothane in the transmembrane region of the nAChR.