Changes in Lectin-Binding Sites on the Thyroid Follicle Cell Surface Shown by the Ferritin-Labeling Technique

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Lectin-binding sites on the porcine thyroid follicle cell surface wereexamined using ferritin conjugated Ricinus communis agglutinin (Fer-RCA) as a cytochemical stain for sugar residues on the plasma membranes. The porcine thyroid gland was dissociated in an enzyme solution containing collagenase and trypsin. The dissociated non-cultured cells and the disso-ciated then cultured cells, either unfixed or aldehyde-fixed, were labeled with Fer-RCA and processed for transmission electron microscopy. On aldehyde-fixed cells, the tagged ferritin particles representing RCA-binding sites were more abundant at the apical surface than at the baso-lateral surface. On unfixed cells, patchy and sparse redistribution of the Fer-RCA binding sites was seen on the baso-lateral surfaces, whereas on the apical surfaces it was not clear. Recovery of the binding capacity for Fer-RCA at the baso-lateral cell surfaces took place within 1 h, when Fer-RCA-labeled, unfixed, disso-ciated cells were incubated in the culture medium without Fer-RCA. The en-zymatic dissociation procedure did not seem to change the RCA-binding sites in terms of number and the distribution pattern over all the cellsurfaces, but to some degree it caused higher mobility and easier detachment of RCA-binding sites on the unfixed baso-lateral cell surfaces. We concluded that thyroid follicle cells have regional differences for their RCA-binding sites in the distribution and redistribution patterns between the apical and the baso-lateral cell surfaces. These regional differences in the RCA-binding sites may represent plasma membrane polarity, morphologically and functionally, in these highlyorganized tissue cells.

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