In vitro calcium deposition by rachitic rat matrix vesicles: nucleoside triphosphate supported calcium deposition

The present study was designed to test whether ATP at serum levels can support matrix vesicle-mediated Ca deposition while the final Ca x P ion product is maintained at or below serum or cartilage fluid levels. Rachitic rat epiphyseal cartilage matrix vesicles (40 micrograms protein/ml) in a simple calcifying solution (without exogenously added Pi) containing 50 mM Tris, pH 7.6 at 37 degrees C, 0.1 M NaCl, 1.35 mM CaCl2, 1 mM ATP, deposited about 500 nmol Ca/mg protein after 5 h. The amount of Ca deposited increased with increases in incubation time, concentrations of ATP, Ca2+, hydroxide, and matrix vesicle protein. UTP, GTP, and CTP were equally effective in supporting Ca deposition by matrix vesicles. ATP-alpha,beta-methylene and ATP-beta,gamma-methylene were inhibitory for ATP-dependent Ca deposition. Experiments with limiting amounts of ATP and Ca2+ available in the calcifying solution indicated that ATP concentration at serum levels, in the presence of Ca x P ion products at serum or cartilage fluid levels, can support matrix vesicle-mediated Ca deposition.