Autoradiographical studies on the localization of metallothionein in proximal tubular cells of the rat kidney.

The renal distribution of 125I-labelled metallothionein (125I-MT), administered as a tracer dose to female Wistar rats, has been investigated by light and electron microscopical autoradiography. 125I-MT was absorbed rapidly and 80% of the administered dose was observed in the kidney within 60 min after dosing. At 30 min, a high density of silver grains due to 125I, was observed by light microscopy in the convoluted proximal tubules. Electron microscopical autoradiography showed that silver grains were located in large apical vacuoles and cytoplasmic bodies (heterolysosomes) of the endocytotic system in the apical or middle regions of the cells lining convoluted proximal tubules. The results suggest that endocytotic systems are associated with 125I-MT absorption by epithelial cells lining the renal convoluted proximal tubules. The apparent inconsistency on the distribution pattern of silver grains due to 109Cd-labelled MT and 125I-labelled MT in these is also discussed.