Aim:To examine the subcellular distribution of the 3 α_1-adrenoceptor(α_1-AR)subtypes and their internalization and trafficking upon agonist stimulation in hu-man embryonic kidney 293A cells.Methods:Confocal real-time imaging,enzymelinked immunosorbent assay(ELISA)and whole cell[~3H]-prazosin binding assaywere applied to detect the distribution and localization of the 3 α_(1B)-AR subtypes.Results:α_(1A)-AR was found both on the cell surface and in the cytoplasm;α_(1B)-AR,however,was predominantly detected on the cell surface,while α_(1D)-AR wasdetected mainly in the intracellular compartments.After stimulation withphenylephrine,localization changes were detected by confocal microscopy forα_(1A)-and α_(1B)-AR, but the localization of α_(1D)-AR were unaffected.Phenylephrinestimulation promoted a more rapid internalization of α_(1B)-AR than α_(1A)-AR.α_(1D)-ARinternalization was detected only by ELISA.Whole cell[~3H]-prazosin bindingassay showed that α_(1A)-AR functional receptors were detected both on the cellsurface and in the cytoplasm;α_(1B)-AR,however,were detected predominantly onthe cell surface,while α_(1D)-AR were detected mainly in intracellular compartments.Phenylephrine stimulation promoted internalization of α_(1A)-and α_(1B)-AR.Conclusion:Phenylephrine stimulation induced changes in the localization of the3α_1-AR. Aim: To examine the subcellular distribution of the 3α_1-adrenoceptor (α_1-AR) subtypes and their internalization and trafficking upon agonist stimulation in hu-man embryonic kidney 293A cells. Methods: Confocal real-time imaging, enzyme linked immunosorbent assay (ELISA) and whole cell [~ 3H] -prazosin binding assaywere applied to detect the distribution and localization of the 3 alpha-1 (1B) -AR subtypes.Results: alpha 1A (IA) -AR was found both on the cell surface and in the cytoplasm; (1B) -AR, however, was predominantly detected on the cell surface while α_ (1D) -AR wasdetected mainly in the intracellular compartments. After fir with phenylephrine, localization changes were detected by confocal microscopy for α_ (1A) -and α_ ) -AR, but the localization of α - (1D) -AR were unaffected. Phenylephrine promoted promoted more rapid internalization of α_ (1B) -AR than α_ (1A) -AR.α_ (1D) -ARinternalization was detected only by ELISA. Whole cell [~ 3H] -prazosin bindingassay showed that α_ (1A) -AR functional rece p1 was detected predominantly on the cell surface while α_ (1D) -AR were detected mainly in intracellular compartments. Phenylephrine stimulation promoted internalization of α_ (1A) ) -and α_ (1B) -AR.Conclusion: Phenylephrine stimulation induced changes in the localization of the 3α_1-AR.