Characterization of calcium accumulation in the brain of rats administered orally calcium: The significance of energy-dependent mechanism

Primary cultures of rat hepatocytes maintained on different matrix proteins such as collagen (Co IV) fibronectin (Fn), Laminin (Ln) or different tissue biomatrices were metabolically labelled with ³⁵S]-SO₄ and the synthesis of sulphated proteoglycans was studied. The incorporation of the label into total glycosaminoglycan (GAG) was significantly higher in cells maintained on Co IV compared to those maintained on Fn or Ln. Similarly the incorporation of label was maximum in those cells maintained on the aortic biomatrix compared to liver or mammary gland biomatrix. About 80–95% of the GAG synthesised and secreted by cells maintained on individual matrix proteins and liver biomatrix was heparan sulphate (HS). But in the case of cells maintained on collagen IV aortic or mammary biomatrix in addition to HS, significant amount of chondroitin sulphate (CS) was also found. Nearly 50% of the total ³⁵S]-GAG was associated with the cell layer after 24 h in culture in the case of cells maintained on individual matrix protein while those maintained on tissue biomatrix, retained about 70% of the ³⁵S]-labelled proteoglycans (PG) with the cell layer. Analysis of the cell surface ³⁵S]-labelled proteoglycans isolated from cells maintained on different biomatrix showed that it is a hybrid proteoglycan consisting of CS and HS. While the PG isolated from cells maintained on liver biomatrix consists of HS and CS in the ratio of 3:2 that from cells maintained on aorta or mammary gland matrix was about 2:3 indicating an alteration in the nature of the cell surface PGs produced by cells maintained on different tissue biomatrix. These results indicate that depending on the nature of the matrix substratum with which the cells are in contact, the nature and quantity of sulphated proteoglycans produced by hepatocytes vary.