Reduced Protein Expression of the Na+/Ca2++K+-Exchanger (SLC24A4) in Apical Plasma Membranes of Maturation Ameloblasts of Fluorotic Mice

Exposure of forming enamel to fluoride results into formation of hypomineralized enamel. We tested whether enamel hypomineralization was caused by lower expression of the NCKX4/SLC24A4 Ca2+-transporter by ameloblasts. Three commercial antibodies against NCKX4 were tested on enamel organs of wild-type and Nckx4-null mice, one of which (a mouse monoclonal) was specific. This antibody gave a prominent staining of the apical plasma membranes of maturation ameloblasts, starting at early maturation. The layer of immuno-positive ameloblasts contained narrow gaps without immunostaining or with reduced staining. In fluorotic mouse incisors, the quantity of NCKX4 protein in ameloblasts as assessed by western blotting was not different from that in non-fluorotic ameloblasts. However, immunostaining of the apical plasma membranes of fluorotic ameloblasts was strongly reduced or absent suggesting that trafficking of NCKX4 to the apical membrane was strongly reduced. Exposure to fluoride may reduce NCKX4-mediated transport of Ca2+ by maturation stage ameloblasts which delays ameloblast modulation and reduces enamel mineralization

Microradiography to evaluate bone growth into a rat mandibular defect

Microradiography has been evaluated to measure bone heating into a 5.0 mm outer diameter mandibular defect in the rat. This method provides high-resolution radiographs of the defects that can be used for an accurate measurement of bone defect heating. In 12 rats, the defect widths of 42-day-old mandibular defects have been measured both using microradiographs and histological, sections. The defect width +/- S.D. measured 3.42 +/- 0.98 mm microradiographicatly and 3.47 +/- 1.11 mm histologically. Both methods were accurate in determining defect widths but microradiography has the advantage over histology that an image is obtained from the entire defect, making it possible to measure areas of bone growth. (C) 2003 Elsevier Science Ltd. All rights reserved