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The effect of essential trace metals on bone metabolism was investigated in the femoral diaphysis of weanling rats. Oral administration of zinc (1.53-306 mumol/100 g body weight) for 3 days produced significant increases in alkaline phosphatase activity and DNA content. These biochemical indices were also increased by oral administration of chromium (III), cobalt, copper, manganese, and nickel with the dose of 1.53 mumol/100 g. With the dose of 15.3 mumol/100 g of above all metals, except zinc, the enzyme activity was significantly decreased in comparison with control, while DNA content was not decreased significantly. Moreover, the effect of zinc on alkaline phosphatase activity and DNA content was not enhanced by simultaneous administration of other metals (1.53 mumol/100 g). The present study indicates that, of the essential trace metals, zinc can effectively stimulate the bone growth and calcification with comparatively higher dose levels. This suggests a nutritional significance of zinc on bone growth.

Heat shock stress induces some heat shock proteins, including Hsp70, and activates sodium-dependent glucose transport in porcine renal LLC-PK 1 cells, but its mechanisms have not been described in detail. We investigated whether sodium-dependent glucose transporter (SGLT1) interacts with Hsp70 to increase SGLT1 activity. Heat shock stress increased SGLT1 activity without changing SGLT1 expression. The increase of SGLT1 activity was completely inhibited by an antitransforming growth factor-␤1 (TGF-␤1) antibody. Instead of heat shock stress, TGF-␤1 increased SGLT1 activity dose-and time-dependently without changing SGLT1 expression. We found that the amount of Hsp70 immunoprecipitated from TGF-␤1-treated cells with an anti-SGLT1 antibody was higher than that of the control cells. Transfection of an anti-Hsp70 antibody into the cells inhibited the increase of SGLT1 activity. With confocal laser microscopy, both SGLT1 and Hsp70 was localized near the apical membrane in the TGF-␤1-treated cells, and an anti-Hsp70 antibody disturbed this localization. Furthermore, we clarified that an anti-Hsp70 antibody inhibited interaction of SGLT1 with Hsp70 in vitro. These results suggest that Hsp70 forms a complex with SGLT1 and increases the expression level of SGLT1 in the apical membrane, resulting in up-regulation of glucose uptake.