Internalization and distribution of three α1-adrenoceptor subtypes in HEK293A cells before and after agonist stimulation

IM: To examine the subcellular distribution of three α1-adrenoceptor (α1-AR) subtypes and their internalization and trafficking upon agonist stimulation in human embryonic kidney (HEK) 293 cells. METHODS: Confocal real-time imaging, ELISA and whole cell 3H-prazosin binding assay were applied to detect the distribution and localization of three α1-AR subtypes. RESULTS: α1A-AR was found both on the cell surface and in the cytoplasm; α1B-AR, however, was predominantly detected on the cell surface while α1D-AR was detected mainly in the intracellular compartments. After stimulation with phenylephrine, localization changes were detected by confocal microscopy for α1A- and α1B-ARs but localization of α1D-ARs was unaffected. Phenylephrine stimulation promoted a more rapid internalization of α1B-ARs than α1A-ARs. We were able to show α1D-AR internalization only when assayed by enzyme-linked immunosorbent assay (ELISA). Whole cell 3H-prazosin binding assay showed that α1A-AR functional receptors were detected both on the cell surface and in the cytoplasm; α1B-ARs, however, were detected predominantly on the cell surface while α1D-ARs were detected mainly intracellularly. Phenylephrine stimulation promoted internalization of α1A- and α1B-ARs. CONCLUSION: These results suggest that phenylephrine stimulation could induce changes in the localization of the three α1-ARs.