title: Agonist-induced internalisation of the angiotensin II-binding sites from plasma membranes of isolated rat hepatocytes.
abstract: Angiotensin II (Ang II) provokes rapid internalisation of its receptor from plasma membranes in isolated rat hepatocytes. After 10 min stimulation with Ang II, plasma membrane lost about 60% of its 125I-Ang II-binding capacity. Internalisation was blocked by phenylarsine oxide (PhAsO), whereas okadaic acid, which markedly reduced the sustained phase of calcium mobilization, did not have a preventive effect on Ang II-receptor complex sequestration. These data suggest that Ang II receptor internalisation is probably independent of a phosphorylation/dephosphorylation cycle of critical serine/threonine residues in the receptor molecule. To establish a relationship between sequestration of the Ang II receptor and the physical properties of the Ang II-binding sites, 125I-Ang II-receptor complex profiles were analysed by isoelectric focusing. In plasma membrane preparations two predominant Ang II-binding sites, migrating to pI 6.8 and 6.5, were found. After exposure to Ang II, cells lost 125I-Ang II-binding capacity to the Ang II-receptor complex migrating at pI 6.8 which was prevented in PhAsO-treated cells. Pretreatment of hepatocytes with okadaic acid did not modify Ang II-receptor complex profiles, indicating that the binding sites corresponding to pI 6.5 and pI 6.8 do not represent a phosphorylated and/or non-phosphorylated form of the Ang II receptor. The results show that the Ang II-receptor complex isoform at pI 6.8 represents a functional form of the type-1 Ang II receptor. Further studies are necessary to identify the Ang II-related nature of the binding sites corresponding to pI 6.5.
authors.affiliation: Departamento de Bioquímica y Biología Molecular, Facultad de Medicina, Universidad de Málaga, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Montiel
authors.forename: M C
authors.initials: MC
authors.lastname: Caro
authors.forename: E
authors.initials: E
authors.lastname: Jiménez
mesh_terms: D000804:Angiotensin II / Q000378:metabolism*; D000818:Animals; D001152:Arsenicals / Q000494:pharmacology; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism*; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007477:Ions; D007525:Isoelectric Focusing; D007536:Isomerism; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D008297:Male; D019319:Okadaic Acid / Q000494:pharmacology; D011485:Protein Binding; D051381:Rats; D017208:Rats, Wistar; D011945:Receptors, Angiotensin / Q000378:metabolism*
chemical_list: D001152:Arsenicals; D004791:Enzyme Inhibitors; D007477:Ions; D011945:Receptors, Angiotensin; C029341:oxophenylarsine; D000804:Angiotensin II; D019319:Okadaic Acid; D002118:Calcium