Intracellular osteoblastic cell

Interestingly, Quarles found osteoblast cells in culture required serum for complete mitogenic action (Quarles et al. 1991). While he considered that this might be to trigger the signal transduction pathway (e.g., PTH contamination) an alternative possibility is that Tf inclusion in serum improved Al delivery to its intracellular site of action. Al modulation of G protein function is an attractive theory for the biphasic mechanism(s) of mitogenic action and inhibition (see Sect. G), particularly since Al could act alone or combined with F to have differing effects. 

Donahue, S.W., Donahue, H.J., and Jacobs, C.R., Osteoblastic cells have refractory periods for fluid-flow-induced intracellular calcium oscillations for short bouts of flow and display multiple low-magnitude oscillations during long-term flow, /. Biomech., 36, 35, 2003. 

Long GJ, Rosen JF. 1994. Lead perturbs 1,25 dihydroxyvitamin D3 modulation of intracellular calcium metabolism in clonal rat osteoblastic (ros 17/2.8) cells. Life Sci 54(19) 1395-1402. 

Very little work has been reported on the role of oxidative stress in osteoblasts. However, osteoblasts can be induced to produce intracellular ROS (Cortizo et al., 2000 Liu et al., 1999), which can cause a decrease in alkalinephosphatase (ALP) activity that is partially inhibited by vitamin E and cause cell death (Cortizo et al., 2000 Liu et al., 1999). Treatment of rat osteosarcoma ROS 17/2.8 cells with tumor necrosis factor-alpha (TNF-a) suppressed bone sialoprotein (BSP) gene transcription through a tyrosine kinase-dependent pathway that generates ROS (Samoto et al., 2002). H202 modulated intracellular calcium (Ca2+) activity in osteoblasts by increasing Ca2+ release from the intracellular Ca2+ stores (Nam et al., 2002). 

Fluoroaluminate complexes can mimic the action of many hormones, neurotransmitters, and growth factors. G-protein-mediated cell responses are key steps in neurotransmission and intercellular signaling in the brain [20], and TFA acts as an active stimulatory species [21]. Exposure of osteoblasts to TFA results in a marked potentiation of intracellular orthophosphate transport, alluding to the anion s ability to increase bone mineralization [22]. Brief exposure to aluminum fluoride complexes induces prolonged enhancement of synaptic transmission [23] and can potentially affect the activity of many other ion channels and enzymes in the kidney [24]. Rapid and dynamic changes of the cytoskeletal actin network are of vital importance to the motility of many cells, and TFA induction effects a pronounced and sustained... 

With the isolated perfused duodenum, there is a rapid increase in calcium transport in response to the addition of calcitriol to the perfusion medium. Isolated enterocytes and osteoblasts also show a rapid increase in calcium uptake in response to calcitriol. It is not associated with changes in mRNA or protein synthesis, but seems to be because of recruitment of membrane calcium transport proteins from intracellular vesicles to the cell surface. It is inhibited by the antimicrotubule compound colchicine. It can only be demonstrated in tissues from animals that are adequately supplied with vitamin D in vitamin D-deficient animals, the increase in intestinal calcium absorption occurs only more slowly, together with the induction of calbindin. 

In osteoblasts, keratinocytes, and colonocytes, andpossibly other cells, calcitriol acts via cell surface receptors linked to phospholipase C, resulting in release of diacylglycerol and inositol trisphosphate (Section 14.4.1), followed by opening of intracellular calcium channels and activation of protein kinase C and mitogen-activated protein (MAP) kinases. The effect of this is inhibition of cell proliferation and induction of differentiation. A variety of analogs of calcitriol that do not bind to the nuclear receptor do bind to, and activate, the cell surface receptor, including l,25-dihydroxy-7-dehydrocholesterol and 1,25-dihydroxylumisterol. The rapid nongenomic responses to vitamin D can be demonstrated in knockout mice that lack the vitamin D nuclear receptor (Farach-Carson and Ridall, 1998 Nemere and Farach-Carson, 1998). 

During the investigation of the calcium entry pathways activated by palytoxin in cultured nemons, we observed that the toxin caused a rapid intracellular acidification. Since pH plays a pivotal role in signal transdnction in several cell models, we have examined the effect of palytoxin on intracellnlar pH. Previons stndies have shown that palytoxin indnces cell acidification in embryonic chick ventric-nlar cells (Frelin et al. 1990) and osteoblasts (Momoe and Tashjian 1995). In primary cultures of CGC, palytoxin from 0.1 to 50 nM indnced a dose-dependent intracellnlar acidification (Fig. 6.4). As in the case of calcinm increase indnced by palytoxin, the pH decrease was significant at palytoxin concentrations as low as 1 nM (p < 0.01). Maximnm intracellnlar acidification was observed for palytoxin concentrations of 10, 25, and 50 nM (p < 0.001). At these concentrations, palytoxin decreased pH by 0.6 nnits. The effect of palytoxin on pH was immediate after addition of the toxin. 

Calcitriol behaves like a steroid hormone. It is transported to the nucleus of renal distal tubule cells, intestinal epithelial cells, osteoclasts, and osteoblasts where it induces calbindins, vitamin D-dependent calcium binding proteins. Calbindins mediate the intracellular movement of calcium, from diet to blood, from blood to osteoid matrix, or from bone to blood. There are two calbindin proteins, each encoded by separate genes, one of molecular weight about 9 kDa (calbindin-D. ) and one of molecular weight 28 kDa (calbindin-D28K). Each binds micromolar amounts of calcium and each disappears from animals that are... 

In primary cultures of cerebellar neurons, palytoxin also caused a rapid intracellular acidification. Previous work had shown palytoxin-induced intracellular acidification in chick ventricular cells and osteoblasts. The acidification induced by the toxin was reported to be dependent on the opening of proton-conductive pathways in the plasma membrane or to be a secondary effect of the interaction of the toxin with the sodium pump, respectively. In primary neuronal cultures, palytoxin caused a fast and irreversible intracellular acidification. The decrease in intracellular pH (pHj) caused by palytoxin was already maximal at toxin concentrations of 1 nM (Figure 31.4) at this concentration, palytoxin decreased intracellular pH by 0.6 units. 

Wali, R.K., Kong, J., Sitrin, M.D., et al. 2003. Vitamin D receptor is not required for the rapid actions of 1,25-dihydroxyvitamin D3 to increase intracellular calcium and activate protein kinase C in mouse osteoblasts. J. Cell. Biochem. 88(4) 794—801. 

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