ACTIVATION AND INTERNALIZATION OF CORONARY ENDOTHELIAL LUMINAL MEMBRANE (CELM) AT1 RECEPTOR CAN BE DISSOCIATED

Abstract

Intracoronary prolonged infusion of Ang II and Ang II‐POL; a non diffusible large agonist cause a AT1R‐mediated positive inotropic effects with different time courses; Ang II‐POL effects are sustained and reversible, while Ang II's are transient indicating desensitization. In addition, Ang II induce tachyphylaxis to Ang II and Ang II‐POL, but Ang II‐POL does not. In vitro, desensitization and tachyphylaxis are associated with AT1R internalization. Thus, transient effects of sustained intracoronary Ang II result from gradual internalization of CELM's AT1R, not being the case for Ang II‐POL. To test this hypothesis we measured AT1R levels on CELM. CELM proteins were isolated from hearts perfused with Ang II for 0 to 10 min and from hearts perfused with ang II‐POL 0 to 15 min. AT1R band was identified by Western blot and its mass measured as band optical density (BOD) as respect to 0 time (BOD control = 1.0). Ang II perfusion caused a time‐dependent CELM's AT1R decrease that reached a value of 0.5 at 6 min which rose to reach 1.0 at 10 min. In contrast, Ang II‐POL CELM's AT1R values at various times remained as 1.0, i.e. there was not internalization. These results indicates that: Ang II activates CELM's AT1R and induces its internalization; while Ang II‐POL activates CELM's AT1R without inducing internalization