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Table 1. The radioactivities and ratios of 45Ca to 32PO4 in the enamel and dentin of lower incisor. The positions of the sample dissected are indicated in figure 4-A. 45Ca* and 32PO4* indicate the amount of radioactive calcium and phosphate transported through a unit area(1000$B%
(Jm2) of cell layer into mineralizing front. Counts are mean $B!^(J SD.

Table 2. The radioactivities and ratios of 45Ca to 32PO4 in the developing bone. The positions of the sample dissected are indicated in figure 4-B, and the sample of BN6 was dissected from calvaria. Counts are mean $B!^(J SD.


Fig. 1. (A); Distribution of calcein fluorescence in the lower incisor of a 9-day-old rat 30 seconds after an i.v. injection. X 11. (B); the areas indicated with arrow A in (A) at a high magnification. X 180. Arrows in (B) show the fluorescence in the spaces between ameloblasts. T = transitional stage; SA = area of smooth-ended ameloblasts; RA = area of ruffle-ended ameloblasts; PL = papillary layer; Am = ameloblast layer; En = enamel; Dn = dentin; Od = odontoblast layer.

Fig. 2. Contact autoradiographs of the lower incisor of a 9-day-old rat 30 seconds after an i.v. injection of 45CaCl2. Arrow heads indicate the weak labeled areas in the odontoblast layer. White areas correspond to the high radioactive regions. Abbreviations the same as in Figure 1. X 11.

Fig. 3. Light microscopic autoradiographs of the ameloblast layer(A,B) and the odontoblast layer(C,D) of a 9-day-old rat 30 seconds after an i.v. injection of 45CaCl2. (A); area of smooth-ended ameloblasts. X 520. (B); area of ruffle-ended ameloblasts. X 520. (C); area indicated with arrow A in figure 2. X 520. (D); area indicated with arrow B in figure 2. X 600. Arrows in (B,D) indicate the cells heavily labeled. Abbreviations the same as in Figure 1.

Fig. 4. Schematic drawings showing the position of sample dissected from the freeze-dried section of lower incisor and long bone of rat. SA1 = area of smooth-ended ameloblasts; RA1, RA2 = area of ruffle-ended ameloblasts.

Fig. 5. (A); Distribution of calcein fluorescence in the metaphysis of tibia of a 9-day-old rat 5 minutes after an i.p. injection. X 17. Contact autoradiograph(B) and light microscopical autoradiograph(C) of the metaphysis 5 minutes after an i.p. injection of 45CaCl2. White areas in (B) and black label in (C) correspond to the high radioactive regions. B: X 17. C: X 50.

Fig. 6. Light microscopic autoradiograph of the trabeculae in the primary spongenous of tibia 30 seconds after an i.v. injection of 45CaCl2. Arrows indicate the intensively labeled cells, and line indicate the surface of bone. Bn = bone. X 1500.

Fig. 8. Diagrams showing the movement of calcium in mineralizing tissue. The ratios of calcium to phosphate ion transported into the mineralizing front are increased from left(A) to right(D). (A): Distal cellular junctions are opened. The net flux within the cell is directed to the intercellular spaces as Ca-pumps are located in all area of cell membrane. (B): Distal cellular junctions are opened, and calcium ion is moved to the mineralizing front through the extracellular route by simple diffusion. (C): Distal cellular junctions are opened, and Ca-pumps are localized on the distal cell membrane. Calcium ion is translocated to the mineralizing front by simple diffusion and by Ca-pump. (D): Distal cellular junctions are tightly closed, and Ca-pump is localized on the distal cell membrane. Calcium ion is transported to the mineralizing front by Ca-pump.