Na-K-ATPase in the Enamel Organ: Localization and Possible Roles in Enamel Formation

¹ Department of Oral Biology and Pathology, School of Dental Medicine
² Department of Anatomical Sciences, School of Medicine, Health Sciences Center, State University of New York, Stony Brook, New York 11794-8700

Ouabain-sensitive, K-dependent p-nitrophenyl phosphatase (p-NPPase) activity was localized ultracytochemically in the lateral plasma membranes of secretory ameloblasts and the stratum intermedium and principally in the papillary layer cells of aldehyde-fixed rat incisor enamel organs by the one-step lead method. Daily intraperitoneal injection of ouabain (250 µg, 500 µg, and 1 mg/100 g body weight) for two weeks reduced p-NPPase activity in the enamel organ cells. However, the degree to which this activity was reduced appeared to vary among the experimental animals. Addition of ouabain to the cytochemical incubation medium completely inhibited p-NPPase activity in the tissues. Although long-term ouabain injection did not result in any morphological alterations of the enamel organ cells, it caused, in part, an appearance of electrondense, homogeneous matrix-like substances (MS) in the extracellular spaces of the ameloblast layers at both the secretion and maturation stages. In addition, long-term ouabain injection appeared to have resulted in delayed maturation of enamel as measured by energy-dispersive x-ray analysis of Ca and P in surface enamel. These results suggest that Na-K-ATPase of enamel organ cells may participate in the net flow (removal) of organic matrix components and water from the enamel during the maturation stage of enamel formation. It is suggested that this flow is maintained by local osmotic gradients generated by Na-K-ATPase within the papillary layer.

Note:

The authors would like to thank Ms. Elena Camarero for her secretarial assistance in this project and Mrs. Kris Vandenberg for typing the manuscript.

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