3H-dihydromorphine binding sites in subcellular fractions of rat striatum

Binding of low concentrations of 3H-dihydromorphine (3H-DHM) that label specifically opiate mu receptors was tested in the whole particulate (P1 + P2), P1 and P2 fractions of rat striatal homogenate. Two subpopulations of 3H-DHM binding sites were revealed by Scatchard analysis in the whole particulate and in P2 fractions: high-affinity sites of KD approx. 0.2 nM, and low-affinity sites of KD approx. 3 nM. In P1 fraction only one population of low-affinity binding sites was present. Assuming that opiate receptors are predominantly located on synaptosomal membranes, it may be concluded that only high affinity 3H-DMH binding sites represent opiate mu receptors.