Hht. Hsu et Hc. Anderson, EFFECTS OF ZINC AND DIVALENT-CATION CHELATORS ON ATP HYDROLYSIS AND CA DEPOSITION BY RACHITIC RAT MATRIX VESICLES, Bone, 17(5), 1995, pp. 473-477
Elsewhere it has been shown that zinc is highly concentrated in the hy
pertrophic zone of epiphyseal cartilage, It has also been shown that z
inc deficiency can result in abnormal bone development, suggesting a d
irect or indirect role for zinc in calcification, Because matrix vesic
les have been implicated in the initiation of calcification, we tested
the effect of zinc and its chelators, such as EGTA and phenanthroline
, on ATP-dependent Ca uptake by rat matrix vesicles, EGTA pretreatment
of matrix vesicles inhibited ATP-dependent Ca uptake by 50%. To see i
f zinc depletion by EGTA pretreatment is responsible for decreased lev
els of ATP-dependent Ca uptake, ZnCl2 concentrations, ranging from 5 t
o 100 mu mol/L, were tested for their ability to restore Ca deposition
, Zinc exerted a striking enhancing effect on ATP-dependent Ca uptake
of both untreated and EGTA-pretreated matrix vesicles in a dose-depend
ent manner. A 50% activation occurs at about 16 mu mol/L Zn2+. At 63 m
u mol/L Zn2+, there was a fourfold increase in Ca-depositing activity,
Addition of an excess amount of phenanthroline relative to Zn2+ conce
ntration to the reaction mixture faded to abolish activation of Ca upt
ake by Zn2+, indicating that the putative chelator-Zn2+ complex format
ion did not prevent activation, The observed partial inhibition of ATP
ase and the activation of ATP-dependent Ca uptake of Zn2+ suggest that
, in addition to ATPase, some other Ca and/or Pi uptake activators res
ponsive to Zn2+ treatment are present in mammalian matrix vesicles.