Upregulation of the mu-noncompetitive delta binding site by chronic morphine administration: effect of preincubating membranes in 400 nM sodium chloride.

Rats treated chronically with morphine were found to have an increased number of mu-noncompetitive delta binding sites. The increase in the Bmax was 39% and the enhancement was blocked by pre-incubation in 50 mM Tris, pH 7.4 with 400 mM NaCl for one hour at 25 degrees C. These findings are consistent with the removal of newly manifested binding sites being a specific property of sodium, by analogy with previous studies where sodium has been shown to extract extrinsic proteins from red cell ghosts.