title: Molecular weight of different angiotensin II polymers directly determines: density of endothelial membrane AT1 receptors and coronary vasoconstriction.
abstract: We have shown that angiotensin II (Ang II) does not diffuse across the vessel wall, remaining intravascularly confined and acting solely on the coronary endothelial luminal membrane (CELM) receptors. A sustained intracoronary infusion of Ang II causes transient coronary vasoconstriction (desensitization) due to membrane internalization of CELM Ang II type 1 receptors (CELM-AT1R). In contrast, sustained intracoronary infusion of a non-diffusible polymer of Ang II (Ang II-Pol, 15,000 kDa) causes a sustained vasoconstriction by preventing CELM-AT1R internalization. In addition, a sustained intracoronary infusion of Ang II leads to a depressed response following a secondary Ang II administration (tachyphylaxis) that is reversed by Ang II-Pol. These findings led us to hypothesize that the rate of desensitization, tachyphylaxis, and AT1R internalization were dependent on Ang II-Pol molecular weight. To test this hypothesis, we synthesized Ang II-Pols of the following molecular weights (in kDa): 1.3, 2.7, 11, 47, 527, 3270 and 15,000. Vasoconstriction was measured following intracoronary infusion of Ang II-Pols in Langendorff-perfused guinea pig hearts at constant flow. The CELM protein fraction was extracted using the silica pellicle technique at different time points in order to determine the rate of AT1R internalization following each Ang II-Pol infusion. CELM-AT1R density was quantified by Western blot. We found that the rate of desensitization and the tachyphylaxis effect varied inversely with the molecular weight of the Ang II-Pols. Inversely proportional to the molecular weight of Ang II-Pol the CELM-AT1R density decreases over time. These results indicate that the mechanism responsible for the decreased rate of desensitization and tachyphylaxis by higher molecular weight Ang II polymers is due to reduction in the rate of CELM-AT1R internalization. These Ang II polymers would be valuable tools for studying the relationship between AT1R internalization and physiological effects.
authors.affiliation: Dept. of Physiology, Facultad de Medicina de la UASLP, Mexico. davtirado@yahoo.com.mx
authors.forename: David
authors.initials: D
authors.lastname: Torres-Tirado
authors.forename: Juan
authors.initials: J
authors.lastname: Ramiro-Diaz
authors.forename: Maureen T
authors.initials: MT
authors.lastname: Knabb
authors.forename: Rafael
authors.initials: R
authors.lastname: Rubio
mesh_terms: D000804:Angiotensin II / Q000008:administration & dosage / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D003331:Coronary Vessels / Q000187:drug effects / Q000378:metabolism; D004730:Endothelium, Vascular / Q000187:drug effects / Q000378:metabolism*; D006168:Guinea Pigs; D008970:Molecular Weight; D011108:Polymers / Q000737:chemistry*; D044140:Receptor, Angiotensin, Type 1 / Q000378:metabolism*; D013997:Time Factors; D014661:Vasoconstriction / Q000187:drug effects*
chemical_list: D011108:Polymers; D044140:Receptor, Angiotensin, Type 1; D000804:Angiotensin II