Immune atomic force microscopy of prestin-transfected CHO cells using quantum dots

Prestin, a membrane protein of the outer hair cells (OHCs), is known to be the motor which drives OHC somatic electromotility. Electron microscopic studies showed the lateral membrane of the OHCs to be densely covered with 10-nm particles, they being believed to be a motor protein. Imaging by atomic force microscopy (AFM) of prestin-transfected Chinese hamster ovary (CHO) cells revealed 8- to 12-nm particle-like structures to possibly be prestin. However, since there are many kinds of intrinsic membrane proteins other than prestin in the plasma membranes of OHCs and CHO cells, it was impossible to clarify which structures observed in such membranes were prestin. In the present study, an experimental approach combining AFM with quantum dots (Qdots), used as topographic surface markers, was carried out to detect individual prestin molecules. The inside-out plasma membranes were isolated from the prestin-transfected and untransfected CHO cells. Such membranes were then incubated with antiprestin primary antibodies and Qdot-conjugated secondary antibodies. Fluorescence labeling of the prestin-transfected CHO cells but not of the untransfected CHO cells was confirmed. The membranes were subsequently scanned by AFM, and Qdots were clearly seen in the prestin-transfected CHO cells. Ring-like structures, each with four peaks and one valley at its center, were observed in the vicinity of the Qdots, suggesting that these structures are prestin expressed in the plasma membranes of the prestin-transfected CHO cells.