AGONIST-INDUCED MORPHOLOGIC DECREASE IN CELLULAR D-1A DOPAMINE-RECEPTOR STAINING

The distribution of D-1A dopamine (DA) receptor proteins was assessed by using subtype specific antireceptor antisera after acute DA exposur e. The immunofluorescent staining of D-1A DA receptor protein expressi on was examined in (1) stably transfected Chinese hamster ovary (CHO) cells, (2) primary striatal cell cultures, and (3) rat striatal brain slices. After agonist exposure as brief as 2 min and as long as 60 min , profound loss of immuno fluorescent D-1A receptor protein staining o ccurred in each paradigm. Additionally in the tissue slice, immunofluo rescent neuropil staining for the receptor protein also was attenuated . The DA-induced alteration in receptor protein staining was blocked b y the antagonist (+)-butaclamol and by the selective D1-family antagon ist SCH 23390. Receptor staining patterns reverted back to the control immunofluorescent distribution within 15 min after removing the agoni st from the bath. Immunofluorescence for the second-messenger cyclic A MP increased at all DA exposure times in the three experimental paradi gms, was blocked by D1-family antagonists, and decreased to basal stai ning after brief recovery periods. This demonstrated the functional in tegrity of the D-1A receptor in target cells. Pretreatment with the mi togenic plant lectin concanavalin A blocked the immunofluorescent decr ease in receptor staining but not the elevation of the second messenge r, indicating a morphologic distinction in these two events, parallel to other biochemical reports. The data suggested that a morphologic ba sis of acute homologous D-1A DA receptor desensitization may be transp osition of membrane-surface receptors to a transiently unavailable, in tracellular compartment. This finding is supported by specific fluores cence incorporation of FM1-43, used as a marker of endocytosis, in CHO cells treated with DA. (C) 1997 Wiley-Liss, Inc.