BINDING OF LISURIDE-H-3 HYDROGEN MALEATE TO STRIATAL MEMBRANES OF RAT-BRAIN

Binding of 3H-lisuride hydrogen maleate (LHM), a dopaminergic agonist, to striatal membranes was inhibited by (+)-butaclamol, whereas (-)- butaclamol at a concentration of 10-9-10-7M was without effect. The difference in the amount of 3H-LHM bound to striatal membranes in the presence of 10-7 M (-)-butaclamol and (+)-butaclamol was designated as the specific binding of 3H-LHM, and its properties were examined. The specific 3H-LHM binding to striatal membranes was saturated with an equilibrium amount of 490 fmol/mg protein and had an apparent dissociation constant (Kd) of 0.5 nM. The specific binding of 3H-LHM to striatal membranes was inhibited by LHM, haloperidol, apomorphine and methysergide with inhibitor association constants (Ki value) of 0.79, 7.1, 100 and 180 nM, respectively. Phentolamine, dopamine, (-)-norepinephrine and serotonin were weaker inhibitors of the specific binding of 3H-LHM to striatal membranes, with Ki values of 1,100, 3,500, 33,000 and 79,000 nM, respectively. No inhibition was observed with (±)-propranolol, dichloroisoproterenol or QNB. These results are discussed in connection with dopamine receptors. © 1979.