Immunoanalogue of vertebrate beta-adrenergic receptor in the unicellular eukaryote Paramecium

Cell fractionation, SDS-PAGE, quantitative Western blot, confocal immunolocalization and immunogold labelling were performed to find an interpretation of the physiological response of the unicellular eukaryote Paramecium to -adrenergic ligands. The 69kDa polypeptide separated by SDS-PAGE in S2 and P2 Paramecium subcellular fractions cross-reacted with antibody directed against human ₂-adrenergic receptor. This was detected by Western blotting followed by chemiluminescent detection. Quantitative image analysis showed that -selective adrenergic agonist (–)-isoproterenol – previously shown to enhance phagocytic activity – evoked redistribution of the adrenergic receptor analogue from membraneous (P2) to cytosolic (S2) fraction. The relative increase in immunoreactive band intensity in S2 reached 80% and was paralleled by a 59% decrease in P2 fraction. Confocal immunofluorescence revealed ₂-adrenergic receptor sites on the cell surface and at the ridge of the cytopharynx – where nascent phagosomes are formed. This localization was confirmed by immunoelectron microscopy. These results indicate that the 69kDa Paramecium polypeptide immunorelated to vertebrate ₂-adrenergic receptor appeared in this evolutionary ancient cell as a nutrient receptor.