Characterisation of AT1 angiotensin receptors on cultured rat intestinal epithelial (RIE-1) cells.
The relative binding affinities of non-peptide antagonists, and the sensitivity of 125I-angiotensin II (125I-AII) binding to the reducing agent, dithiothreitol, indicated the presence of AT1 angiotensin receptors on RIE-1 rat intestinal epithelial cells. Consistent with this finding, AT1 angiotensin receptor mRNA was detected in RIE-1 cells using Northern blotting, whereas no mas transcripts (which also encode an angiotensin receptor) were detectable using a RNAse protection assay. At 37 degrees C, 125I-AII rapidly bound to RIE-1 cells and internalised into an acid-inaccessible compartment, which resulted in the depletion of 125I-AII from the binding medium. Following overnight incubation of RIE-1 cells with 125I-AII at 4 degrees C, the majority of bound ligand was also, unexpectedly, found to be inaccessible to subsequent acid elution. After warming these cultures to 37 degrees C, acid-inaccessible 125I-radioactivity rapidly disappeared from the cells, and 125I-labelled degradation products accumulated in the medium. Scatchard analysis of the concentration-dependent binding of 125I-AII solely to the acid-accessible sites on RIE-1 cells revealed little difference to the KD value obtained from total 125I-AII binding (to both acid-accessible and -inaccessible sites), but only approximately 15% of the number of sites.
Smith
R D
RD
Department of Clinical Biochemistry, Addenbrooke's Hospital, Cambridge, UK.
D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D002460:Cell Line; D006868:Hydrolysis; D007413:Intestinal Mucosa / Q000737:chemistry* / Q000166:cytology; D007457:Iodine Radioisotopes; D017853:Phosphotransferases (Alcohol Group Acceptor); D051381:Rats; D011945:Receptors, Angiotensin / Q000032:analysis*
D007457:Iodine Radioisotopes; D011945:Receptors, Angiotensin; D000804:Angiotensin II; D017853:Phosphotransferases (Alcohol Group Acceptor); C068961:phosphatidylinositol 4,5-biphosphate kinase