Studies on the influx of [3H]-histidine and 45Ca through a surgical opening to rat incisor ameloblasts and adjacent enamel.

Considerable controversy exists about the role of ameloblasts in transport of calcium to mineralizing enamel. The rate and pattern of incorporation of calcium and an enamel precursor (histidine) were studied autoradiographically by introducing the isotopes through a surgically created defect in the lower border of the rat mandible. Influx of the isotopes to both secretory and maturation ameloblasts and adjacent enamel was examined in large survey sections of the entire incisor at intervals of 3 min to 2 h. Substantial concentrations of silver grains were observed over both secretory and maturation ameloblasts within 5 min of placement of either isotope. 45Ca was also present in secretory and maturation enamel within this short time. The overall patterns of influx and uptake of both precursors were similar to those found when such isotopes have been administered parenterally. The amount of influx of 45Ca across secretory, smooth-ended, and ruffle-ended maturation ameloblasts was compared qualitatively and found to be similar. The reproducibility of this surgical technique was demonstrated as well as its usefulness in combination with survey sections for multi-method investigations of rat incisor enamel formation and mineralization.