Autoradiographic, ultrastructural and biosynthetic study of the effect of colchicine on enamel matrix secretion and enamel mineralization in hamster tooth germs in vitro.
First upper molar tooth germs of two to three days old hamsters were exposed in vitro to colchicine in concentrations ranging between 10(-7) and 10(-4) M in the presence of 45Ca and/or [3H]-proline for various times up to 18 h. Enamel mineralization was determined by chemical extraction of in vitro incorporated 45Ca and verified ultrastructurally. Quantitative autoradiography compared with water extracts from total explants radiolabelled with [3H]-proline showed a dose-dependent decrease of grain counts over the extracellular enamel to the similar extent as the decrease in radiolabelled amelogenins in water-extracts. It was concluded that water-extracts from total explants represent amelogenins from the extracellular compartment. Enamel matrix secreted in vitro during exposure to high doses of colchicine failed to mineralize and the complete loss was provoked of the distal parts of the secretory ameloblasts including the distal junctional complexes. Nevertheless, the mineralizing pre-exposure enamel neither hypermineralized nor increased uptake of 45Ca. These data do not support the hypothesis that secretory ameloblasts restrict transepithelial calcium transport by directing most of the calcium ions away from the mineralization front. The biosynthetic data furthermore suggest that enamel matrix proteins, only extractable with guanidine-HCl-EDTA, change their physico-chemical nature during secretory amelogenesis in vitro either during secretion or upon their extracellular mineralization.
Bronckers
A L
AL
Department of Oral Cell Biology, ACTA, Vrije Universiteit, Amsterdam, The Netherlands.
Lyaruu
D M
DM
Bervoets
T J
TJ
Wöltgens
J H
JH
D000566:Amelogenesis / Q000187:drug effects*; D000818:Animals; D001345:Autoradiography; D002118:Calcium / Q000378:metabolism; D003078:Colchicine / Q000494:pharmacology*; D006224:Cricetinae; D066298:In Vitro Techniques; D008854:Microscopy, Electron; D008963:Molar; D014083:Tooth Germ / Q000378:metabolism / Q000648:ultrastructure*
D003078:Colchicine; D002118:Calcium