Abstract
Location of fodrin in the renal tubular epithelium, the epidermal keratinocyte, and the adrenal chromaffin cell was examined by immunofluorescence and immunoelectron microscopy of frozen sections. In most of the renal epithelia, fodrin was confined to the plasma membrane and the terminal web, but in the principal cell of the collecting tubule, it was seen diffusely in the cytoplasm except for the Golgi region. In the epidermis in vivo, fodrin was observed in the cell periphery in the spinous layer, but in the cytoplasm in the basal layer. In a transformed keratinocyte cell line (PAM212), the protein was seen only in the cell surface cultured in standard Ca2+, but in low Ca2+, it was found in the cytoplasm. In the adrenal chromaffin cell in vivo, fodrin was observed only in the plasma membrane, but when massive secretion was induced by insulin, it came to be seen in newly-formed vesicles and vacuoles; a secretory granule membrane protein, cytochrome b561, was also localized in the vesicle, but not in the vacuole. The coexistence of the two proteins in the vesicle was confirmed by the positive labeling of cytochrome b561 in subcellular particles adsorbed to polyacrylamide beads coated with anti-fodrin antibody. The present study showed that fodrin is not always a plasma membrane component and that it could be distributed in the cytoplasm when cells are exposed to various stimuli.
