Biochemical analysis and solubilization of central alpha 1-adrenoceptors in the rat

To study the structure and the molecular mechanisms of action of brain alpha-adrenoceptors, their solubilization was undertaken. alpha 1-Adrenoceptors were first successfully solubilized from fresh rat brain membranes by treatment with 0.3 percent deoxycholate, after prelabeling of the binding site by the highly specific tritiated antagonist 3H-prazosin. The complex thus solubilized underwent a rapid loss of activity at 25 degrees C. Direct solubilization of brain alpha 1-adrenoceptors was obtained by treatment with a new zwitterionic derivative of cholic acid (CHAPS) at a concentration of 5 to 10 mM. The soluble complex was detected by precipitation by polyethylene glycol 6,000 with gamma globulin as a carrier. Binding of 3H-prazosin at 25 degrees C was rapid; at 4 degrees C the steady state was obtained within two hours and remained unchanged for at least six hours. The affinity of the soluble binding site, determined by Scatchard analysis (congruent to 0.6 nM), varied with the concentration of detergent. Specificity of the membrane-bound receptor was preserved as demonstrated by incubation in the presence of alpha 1- and alpha 2-antagonists at various concentrations (by order of potency: prazosin greater than phentolamine greater than yohimbine). Stereoselectivity was also retained in the solubilized binding protein. The solubilization of an active brain alpha 1-adrenoceptor will allow further investigation at the molecular level.