Although the osteocyte is the most abundant among the highly different
iated cells of mature bone (osteocytes, lining cells, osteoblasts, and
osteoclasts), its properties and functions are the least known and un
derstood. Here we isolated osteocytes from mixed populations of bone c
ells liberated from fetal chick calvariae by alternate treatments with
collagenase and EDTA. The osteocytes were removed from the bone cell
populations by binding them via an osteocyte-specific antibody (MAb OB
7.3) to magnetic beads and removing the beads together with the coupl
ed osteocytes from the population using a magnet. Isolated osteocytes
were found to be highly differentiated, postmitotic cells that require
d their typical stellate morphology in culture. Osteocyte populations
had alkaline phosphatase (ALP) activity somewhat lower than that of th
e osteoblast-like cell populations from which they were separated by t
he immunodissection procedure. On the single-cell level, the ALP activ
ity was highly variable. Parathyroid hormone (PTH) receptors were foun
d to be present on osteocytes as well as on osteoblast-like cells, but
not on fibroblast-like cells of the outer periosteum. In response to
PTH, osteocytes increased their intracellular levels of cAMP, as did t
he osteoblast-like cells. Osteocytes appeared to be somewhat more sens
itive to PTH than osteoblasts. When seeded onto dentin slices, osteocy
tes did not corrode the dentin surface to any appraisable degree. We t
herefore found no evidence to support the notion that osteocytes play
a role in the calcium homeostasis through osteocytic osteolysis. Wheth
er osteocytes play an important role in perceiving and transducing hor
monal and/or mechanical stimuli remains open for future research.