AN IMMUNOCYTOCHEMICAL STUDY OF THE ROUTES OF SECRETION OF COLLAGEN AND PHOSPHOPHORYN FROM ODONTOBLASTS INTO DENTIN

Polyclonal antibodies to rat incisor phosphophoryns and to the amino-t elopeptide of the al(I)-chain of type I collagen were used to follow t he pathways of movement of collagen I (COLI) and phosphophoryns (PP) f rom synthesis in the odontoblast to secretion into the mineralized den tin. The antibodies were detected at the transmission electron microsc opic level by their reaction with Protein A-colloidal gold conjugates. Special care was given in specimen preparation to retention of maxima l antigenicity during fixation while maintaining cellular and extracel lular ultrastructure at the mineralization front (MF) in nondeminerali zed sections. Intracellularly, COLI and PP were detected within the en doplasmic reticulum (ER), the Golgi (G) and secretory granules (SG). H owever, as determined by double-immunolabeling with different size gol d particles the COLI and PP were not found together within the same ER , G or SG compartments. PP was localized within the tubular ER, round- shaped transitional vesicles, the Golgi and in narrow asymmetric SG. T hese asymmetric SG were found in abundance in the odontoblastic proces s. PP secretion from these vesicles was near the MF at the predentin-d entin boundary. COLI was localized within rosette form ER compartments , the Golgi and in large, distinctive SG. COLI was deposited at the ce ll-predentin boundary. No COLI SG were seen within the odontoblastic p rocess near the MF. In the region of the MF, prior to mineralization, the PP was localized along the surfaces of the COLI fibrils of the pre dentin. The mineral phase etched surfaces revealed both COLI- and abun dant mineral-associated PP. These data support the hypotheses that, in dentin, the interaction between COLI and PP may initiate crystal nucl eation and that additional interactions between PP and the growing cry stals may modulate the crystal growth pattern and crystal size.