The Effects of Halothane on the Human Beta-adrenergic Receptor of Lymphocyte Membranes

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The effects of halothane on beta-adrenergic receptor antagonist interaction were studied using the membranes of human lymphocytes as a model. Membrane preparations of lymphocytes were obtained from blood samples withdrawn from seven healthy young volunteers. Betareceptor studies were performed using (-)123I iodocyanopindolol (123ICP) binding. Non-specific binding was determined in the presence of (-) isoproterenol. Betareceptor density (Bmax) and the dissociation constant (KD) for 123ICP were determined from saturation curves. Betareceptor affinity for agonists evaluated by the IC50 (the concentration of isoproterenol required to inhibit 50% of specific 123ICP binding) and the dissociation constant (KL) for isoproterenol was established from competition curves. The effect of halothane 1%, in an air oxygen mixture (oxygen fraction: 0.3) administered by tonometry during ligand membrane incubation, on beta-adrenergic receptor, was compared to that of control experiments not exposed to halothane. Halothane produced a moderate but significant decrease of Bmax (-10%) and a significant increase in non-specific binding (+30%), while KD, IC50, and KL were unchanged. The authors conclude that halothane, in vitro, decreases beta-adrenergic receptor density. This effect could be mediated by an alteration of the receptor in the membrane due to action of halothane on the lipid phase of the membrane.

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