Pulsating fluid flow increases prostaglandin production by cultured chicken osteocytes--a cytoskeleton-dependent process.

It has been postulated that the transduction of mechanical stress signals to bone cells occurs via loading-dependent flow of interstitial fluid through the lacuno-canalicular network of bone. We have shown earlier that chicken osteocytes release enhanced amounts of prostaglandin E2 after 1 h treatment with pulsating fluid flow (PFF, 0.5 +/- 0.02 Pa, 5 Hz). Here we study the acute response to PFF on three cell populations derived from fetal chick calvariae, namely periosteal fibroblasts (PF), an osteoblast and osteocyte containing population (OBmix), and osteocytes (OCY), and the involvement of the actin-cytoskeleton in this process. All three cell populations rapidly (OCY: within 5 min, OBmix, PF: within 10 min) increased their release of prostaglandins E2 and I2 in response to PFF, but the response by OCY was 2-4 times higher than that by OBmix or PF. Disruption of the actin-cytoskeleton by cytochalasin B completely abolished the response. We conclude that osteocytes are more sensitive to fluid shear stress than immature bone cells, and that the actin-cytoskeleton is involved in the response to fluid flow.

Permeabilization of cells of hemopoietic origin by extracellular ATP4-: elimination of osteoclasts, macrophages, and their precursors from isolated bone cell populations and fetal bone rudiments.

Skeletal tissues contain, apart from cells of the osteogenic and chondrogenic lineage, cells of hemopoietic origin, e.g., macrophages, osteoclasts, and their precursors. In the present study we examined the sensitivity for extracellular ATP4- of the above-mentioned cell types in freshly isolated, bone-derived cell populations and in explanted fetal metatarsal bones. Cells of hemopoietic origin reacted to the presence of ATP4- with an increased permeability for impermeant cytotoxic molecules, e.g., ethidium bromide (EB), thiocyanate (KSCN), and an increased non-ion selective membrane conductance. As a consequence, these cells could be killed by a short treatment with adenosine-5' triphosphate (ATP)+KSCN. On the other hand, cells of nonhemopoietic origin (e.g., osteoblasts, chondrocytes) were found to be insensitive to ATP4- in this respect. These cells survived the treatment without apparent damage to their alkaline phosphatase activities, osteogenic potentials, and osteoclast induction capacities. The elimination of the endogenous cells of hemopoietic origin from bone tissue or cell populations derived therefrom offers the possibility to study the properties and functions of osteogenic or chondrogenic cells without interference by the presence of cells of hemopoietic origin. It also allows the study of interactions between osteogenic cells and selected cell populations of hemopoietic origin in coculture experiments.

Removal of hematopoietic cells and macrophages from mouse bone marrow cultures: isolation of fibroblastlike stromal cells.

A method is described that permits the removal of hematopoietic cells and macrophages from mouse bone marrow cultures. The method is based on the difference in effect of extracellular ATP4- ions (ATP in the absence of divalent, complexing cations) on cells of hematopoietic origin, including macrophages, and of nonhematopoietic origin, such as fibroblastlike stromal cells. In contrast to fibroblastlike cells, hematopoietic cells and macrophages form under the influence of ATP4- lesions in their plasma membranes, which allows the entrance of molecules such as ethidium bromide (EB) and potassium thiocyanate (KSCN), which normally do not easily cross the membrane. The lesions can be rapidly closed by the addition of Mg2+ to the incubation medium, leaving the EB or KSCN trapped in the cell. This method allows the selective introduction of cell-toxic substances such as KSCN into hematopoietic cells and macrophages. By using this method, fibroblastlike stromal cells can be isolated from mouse bone marrow cultures.

Voltage-activated K+ conductances in freshly isolated embryonic chicken osteoclasts.

Patch-clamp measurements on freshly isolated embryonic chicken osteoclasts revealed three distinct types of voltage-dependent K+ conductance. The first type of conductance, present in 72% of the cells, activated at membrane potentials less negative than -30 to -20 mV and reached full activation at +40 mV. It activated with a delay, reached a peak value, and then inactivated with a time constant of approximately 1.5 s. Inactivation was complete or almost so. Recovery from inactivation, at -70 mV, had a time constant of roughly 1 s. The conductance could be blocked, at least partly, by 4 mM 4-aminopyridine. The second type of conductance (present in all cells) activated at membrane potentials more negative than -40 to -80 mV and reached full activation at -130 mV. Activation potential and maximal conductance were dependent on the extracellular K+ concentration. Inactivation of the conductance first became apparent at membrane potentials more negative than -100 mV and was a two-exponential process. The conductance could be blocked by external 5 mM Cs+ ions. The third type of conductance (present in all cells) activated at membrane potentials more positive than +30 mV. Generally, the conductance did not inactivate.

Cell surface antigens on osteoclasts and related cells in the quail studied with monoclonal antibodies.

The properties of five monoclonal antibodies raised against isolated osteoclasts are described. Osteoclasts were isolated from medullary bone of egg-laying female quails. Mice were immunized with cell preparations consisting for about 10% of multinucleated osteoclasts. A large number of monoclonal antibodies against cell surface antigens were obtained, five of which were extensively characterized by their interactions with different tissues of the quail and their cross-reactivity with other species. Two monoclonals (OC 5.3 and OC 6.8), recognize surface antigens present on osteoclasts, monocytes, granulocytes and endothelial cells, but not on osteoblasts, osteocytes, fibroblasts, lymphocytes, erythrocytes and others. The three other monoclonal antibodies are specific for multinucleated osteoclasts in bone tissue but recognize some cell surface structures in other tissues. Antibody OC 6.9, which in bone tissue stains primarily the surface area of the osteoclast that is adjacent to the resorbing bone surface, also interacts with bile capillaries in the liver and with specific, but not yet identified parts of the nephron. The antibodies OC 6.1 and OC 6.3 interact with Kupffer cells in the liver and tissue macrophages of small intestine. In view of the possible fallacies inherent to the use of cell surface markers for the demonstration of cell relationship and origin, definite conclusions can not yet be made. The fact that the osteoclast, the Kupffer cell and the intestine macrophage are the only cells in bone, bone marrow, liver, kidney and intestine, that share the same surface antigen recognized by monoclonals OC 6.1 and OC 6.3, suggests, however, a common origin for osteoclasts and a number of well described tissue macrophages.