Jp. Iannotti et al., GROWTH-PLATE MATRIX VESICLE BIOGENESIS - THE ROLE OF INTRACELLULAR CALCIUM, Clinical orthopaedics and related research, (306), 1994, pp. 222-229
Isolated bovine growth plate chondrocytes suspended in a synthetic car
tilage buffer containing 10(-7) to 10(-3) M concentrations of calcium
were treated with 1 mu M ionomycin to induce changes in intracellular
ionized calcium as measured by Fura-2 fluroscence. An increase in intr
acellular calcium of 10(-6) to 10(-4) M calcium resulted in the secret
ion of vesicles that contain alkaline phosphatase. An increase in intr
acellular calcium above 10(-4) M resulted in nonspecific cell fragment
ation because of cell damage. Electron microscopy of the secreted vesi
cles demonstrated that their structure resembled matrix vesicles. Isol
ated cells treated with ionomycin (synthetic cartilage buffer with 10(
-6) M calcium) demonstrated intact cell membranes, normal intracellula
r architecture, and numerous plasma membrane processes undergoing vesi
culation. The plasma membrane of these isolated cells and the isolated
vesicles demonstrated a positive stain for alkaline phosphatase. Fres
h growth plate tissue demonstrated plasma membrane staining for alkali
ne phosphatase at the lower proliferative and upper hypertrophic cell
zone, and an increasing number of alkaline phosphatase stained matrix
vesicles in the matrix of the lower hypertrophic cell zone. The data i
ndicate that an increase in intracellular calcium in the lower prolife
rative and hypertrophic cell zones of the growth plate induces the sec
retion of plasma membrane derived matrix vesicles.