Cell-to-substratum contacts in living cells: a direct correlation between interference-reflexion and...

Rat mammary cells growing on glass coverslips were photographed first using interference-reflexion microscopy and then after processing for indirect-immunofluorescence microscopy with antibodies to actin or to alpha-actinin. A comparison of the images of the same cell given by the 2 microscopical procedures indicates that the focal contacts between the cell and the substratum correspond to distal ends of microfilament bundles, and the these bundles are only in limited areas close to the substratum. The focal contracts are rich in alpha-actinin which has been proposed as a membrane-anchorage protein for microfilament bundles. Use of stereo immunofluorescence microscopy allows a direct comparison between the interference-reflexion image, and the underside of the cell after staining with antibodies to actin or alpha-actinin.