Solubilization of rat liver alpha 1-adrenergic receptors. Agonist specific alteration in receptor binding affinity

An improved method for the solubilization of the alpha 1-adrenergic receptors in rat liver, utilizing digitonin, glycerol and sonication, is described. The yield of solubilized receptors was approximately 20%. The soluble receptors showed characteristics similar to the membrane-bound alpha 1 receptors. However, upon solubilization, the affinity for the agonists (-)norepinephrine and (-)epinephrine increased 35- to 66-fold when compared to the affinity in the membranes. The affinity for antagonists remained unchanged. A number of synthetic partial agonists showed a less marked (5- to 10-fold) increase in affinity upon solubilization. These data are consistent with the notion that these receptors might be capable of existing in two distinct conformational states with the high affinity state for agonists being favored by solubilization.