Elevation of [ 3H]cimetidine binding by CuCl 2 in brain membranes of rats

Abstract

Influences of dithiothreitol (DTT), p-chloromercuriphenyl sulfonate (PCMPS) and ascorbate on CuCl 2-induced elevation of [ 3H]cimetidine binding were investigated in brain membranes of rats. CuCl 2 (10–500 μM) elevated specific [ 3H]cimetidine binding in a concentration-dependent manner. There were two types of [ 3H]cimetidine binding in the presence of 50 μM CuCl 2: high affinity binding with K d = 1.97 nM and low affinity with K d = 21.6 nM. PCMPS (10 and 100 μM) reduced the binding in both media with and without CuCl 2. DTT (1–30 μM) or ascorbate (0.1 and 1.0 mM) markedly elevated the binding in the presence of CuCl 2 but showed no effect and ascorbate rather inhibited the binding in the absence of CuCl 2. DTT (0.1 mM) diminished the binding in the presence and absence of CuCl 2. CuCl 2 (50 μM) significantly ( P < 0.01) increased the IC 50 of histamine for [ 3H]cimetidine binding and the effect was greater than that from 100 μM GTP. It is suggested that sulfhydryl groups sensitive to PCMPS could interact with Cu 2+ and thus be involved in an elevation of cimetidine binding. Cu 2+ seems to regulate affinity of agonist binding for cimetidine binding sites presumably by acting on cimetidine binding sites and/or GTP binding regulatory proteins.