Photoincorporation of [ 3H]-chloropromazine into a solubilized bovine striatal preparation

Abstract

Photolysis at 300 nm of [ 3H]-chlorpromazine (CPZ) in the presence of a digitonin-solubilized bovine striatal homogenate results in the formation of a high molecular mass component (>200,000 daltons) which does not arise upon photolysis of either [ 3H]-CPZ or the solubilized preparation separately. Additional components of low molecular mass are observed in both photolyzed and unphotolyzed preparations. The high molecular mass component to which [ 3H]-CPZ binds irreversibly contains a significant fraction of the initial [ 3H] activity. The formation of the high molecular mass component is inhibited by 35 ± 9% when the original photolysis is performed in the presence of 500 nM (+)-butaclamol, an active antagonist of specific binding to postsynaptic dopamine receptors, compared to photolysis in the presence of 500 nM (−)-butaclamol, which has negligible specific affinity for these dopamine receptors. EGTA at a concentration of 5mM has no effect on the photolabeling by [ 3H]-CPZ. SDS-polyacrylamide gel electrophoretic separation of the high molecular mass component shows a major band at ∼61,000 daltons which is not evidenced in the low molecular mass fraction. These observations suggest that upon photoexcitation CPZ may photocrosslink a complex of membrane proteins which includes a neuronal DA receptor.