Agonist-induced internalisation of the angiotensin II-binding sites from plasma membranes of isolated rat hepatocytes.
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.
Montiel
M
M
Departamento de Bioquímica y Biología Molecular, Facultad de Medicina, Universidad de Málaga, Spain.
Caro
M C
MC
Jiménez
E
E
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*
D001152:Arsenicals; D004791:Enzyme Inhibitors; D007477:Ions; D011945:Receptors, Angiotensin; C029341:oxophenylarsine; D000804:Angiotensin II; D019319:Okadaic Acid; D002118:Calcium