Halothane effects on muscarinic acetylcholine receptor complexes in rat brain.

Muscarinic acetylcholine receptors in membranes from rat cerebral cortex or brainstem were equilibrated with halothane (0.5 to 5%). Halothane did not affect the number of [3H]methylscopolamine [( 3H]MS) binding sites. [3H]MS binding affinity, however, was increased in the presence of halothane (KD, air = 0.41 nM; KD, 2% halothane = 0.26 nM). This increase reflected a decrease in the dissociation rate constant (from 13 X 10(-3) min-1 to 6.5 X 10(-3) min-1) rather than a change in the bimolecular rate constant of association (1.8 and 1.9 X 10(7) M-1 min-1 in the absence and presence of 2% halothane respectively). Carbamylcholine affinity for brainstem or cortical muscarinic receptors was not affected by halothane. The ability of a guanine nucleotide to lower carbamylcholine affinity for brainstem receptors, however, was eliminated after equilibration with 2% halothane.