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Biomedical subjects

R Dziak

Publications and source records attributed to R Dziak.

52 records · Page 3Linked to original sources
PubMed1986

The effects of calmodulin antagonists on prostaglandin E2-induced responses in rat calvarial bone cells.

Osteoclastic (OC) and osteoblastic (OB) cells were isolated by sequential collagenase digestions of new-born rat calvaria. Prostaglandin E2(PGE2) did not alter total calmodulin levels after a 5 or 60 min incubation. The calmodulin antagonists, trifluoperazine (TFP) at 10-50 microM and W-7 (50 microM) inhibited PGE2-induced increases in calcium uptake by OC cells, but had no effect on control OC or OB calcium levels. W-5 (50 microM), a chlorine-deficient analogue of W-7 with weak anti-calmodulin activity, had no effect. Compound 48/80 (100-500 micrograms/ml), a highly effective calmodulin antagonist in other systems, had no effect on PGE2-induced calcium levels or control calcium uptake. There was inhibition of PGE2-induced increases in cyclic AMP by compound 48/80 (100 micrograms/ml) in both OC and OB cells but no effect on control levels. TFP at 50 microM inhibited both control and PGE2-induced increases in cyclic AMP but at 10 microM it lessened only the hormone-induced effect. W-7 (100 microM) inhibited PGE2-induced increases in OC and OB cyclic AMP but had no effect on control levels; W-5 (50 microM) had no effect on either of these. Dibutyryl cyclic AMP had no effect on control calcium uptake, PGE2-induced increases or W-7 inhibition of the PGE-2 effect on calcium uptake. The calmodulin antagonists, at doses which had affected only PGE2-induced increases in calcium uptake and/or cyclic AMP production, had no effect on leucine uptake by OC or OB cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Effects of prostaglandins on rat calvarial bone-cell calcium.

Prostaglandin E2 (PGE2) over the concentration range 10(-5)-10(-7) M stimulated calcium uptake in osteoclastic-enriched populations isolated by sequential collagenase digestions of newborn rat calvaria. This effect was on initial calcium uptake occurring at 5 min at 37 degrees C but was not present when isotopic equilibrium was approached (60 min). Prostacyclin (PGI2, PGE1 and PGF2 alpha) stimulated osteoclastic calcium uptake in a similar manner, but with slightly smaller effects than PGE2. Under identical conditions, significant effects of PG were not observed in osteoblastic cells isolated from the same bones by extended collagenase digestions. Combined treatment with PGE2 and parathyroid hormone (PTH) at concentrations which produced no individual effects resulted in a significant increase in calcium uptake in osteoclastic cells. During a 48-h culture period, osteoblastic populations released significantly greater amounts of PGE2 than osteoclastic populations. Pre-incubation for 1 h at 37 degrees C with the prostaglandin cyclo-oxygenase antagonists, indomethacin and flufenamic acid, had no effect on calcium uptake in osteoclastic cells, but resulted in significant decreases in osteoblastic cells. The PGE2-induced increase in calcium uptake on osteoclastic cells was not altered by indomethacin or flufenamic-acid pretreatment. However, after treatment with these inhibitors, a significant response to PGE2 was observed in osteoblastic cells.

Alprostadil↗
PubMed1982

Calcitonin effects on isolated bone cells.

Calcitonin decreased calcium uptake in specific rat bone cell populations obtained by sequential collagenase digestions of calvaria. The calcitonin effect on calcium uptake was observed in the same populations that manifested calcitonin-induced increases in cyclic AMP as well as high levels of acid phosphatase and the ability to release 45Ca from prelabeled devitalized bone. No effect of calcitonin was observed in cell populations that had high levels of alkaline phosphatase and lacked the potential to resorb devitalized bone. These results suggest that changes in cell calcium as well as cyclic AMP may be involved in the mode of action of calcitonin on osteoclast-like cells.

Acid Phosphatase↗
PubMed1982

Effects of synthetic muramyl dipeptide on bone metabolism in the fetal rat.

Synthetic N-acetyl-muramyl-L-alanyl-D-isoglutamine (MDP) stimulated the release of 45Ca from fetal rat long bones in culture for 48 h and also increased the number of osteoclasts per bone and the number of nuclei per osteoclast. It also increased calcium uptake in enriched populations of osteoclasts obtained by sequential collagenase digestions of newborn rat calvaria. This effect was observed after a 120 min incubation with 10(-6) M MDP. Effects of MDP on calcium uptake in osteoblasts were not consistently observed. No effects on cyclic AMP were noted in either osteoclast or osteoblast populations treated with MDP for periods from 1-120 min at 37 degrees C.

Acetylmuramyl-Alanyl-Isoglutamine↗
PubMed1982

Prostacyclin: effects on cyclic AMP in bone cells.

Prostacyclin (PGI2) increased cyclic AMP in specific rat bone cell populations obtained by sequential collagenase digestion of calvariae. An osteoclastic population, characterized by high acid phosphatase levels and the ability to resorb bone in vitro, was more sensitive as reflected by responses to lower doses of PGI2 (2.3 x 10(-8)M) as well as greater responses to higher doses (3.5 x 10(-4)) of PGI2 than the other populations isolated. The osteoblastic populations, characterized by high alkaline phosphatase levels and the inability to resorb devitalized bone did not respond significantly to PGI2 at doses less than 10(-4)M and increases in cAMP were smaller. Then results suggest a differential effect of PGI2 on osteoclasts and osteoblasts which may be involved in the mode of action of endogenously produced PGI2 in bone.

Animals↗
PubMed1980

Effects of a bone resorptive factor from human cancer ascites fluid on rat bone cell calcium and cyclic AMP.

The effects of a bone resorptive protein isolated from human cancer ascites fluid on bone cell calcium and cyclic AMP were studied with fetal rat cells. The osteoclast-activating factor increased bone cell calcium uptake at 37 degrees C and 4 degrees C with no direct effects on calcium efflux. Concentrations of the resorptive factor that increased in vitro bone resorption and cell calcium uptake had no effect on cyclic AMP. The effects of the protein on calcium uptake were not specific for bone cells, and large increases were also observed in isolated fetal rat skin cells. These studies suggest that increases in the permeability of the cell membrane to calcium are involved in the mechanism of action of the ascites fluid resorptive protein.

Animals↗
PubMed1978

Effects of vitamin D3 metabolites on bone cell calcium transport.

The vitamin D3 metabolite, 25-hydroxycholecalciferol, at concentrations of 0.01 to 10.0 microgram/ml, decreased calcium uptake by isolated bone cells. The effect occurred within 1 min after the simultaneous addition of metabolite and 45Ca. Lactic acid and ATP production by the cells was not affected. 24(R), 25-dihydroxycholecalciferol produced a similar decrease in calcium uptake. Vitamin D3 had no effect at concentrations from 0.01 to 10.0 micrograms/ml. No effect of 1,25-dihydroxycholecalciferol on calcium uptake was observed with concentrations from 0.1 to 100 ng/ml and various preincubation periods extending to 2 h. None of the agents had any effect on calcium efflux. The effects of 25-hydroxycholecalciferol and 24(R), 25-dihydroxycholecalciferol on calcium uptake were not seen in isolated fetal rat skin cell preparations.

Adenosine Triphosphate↗
PubMed1976

Responses of fetal rat bone cells and bone organ cultures to the ionophore, A23187.

The ionophore A23187 produced a rapid transient increase in the rate of calcium uptake by isolated fetal rat bone cells. There was no effect on calcium efflux or total cellular calcium. The magnitude of the effect on influx was amplified when the cell were incubated at 4 degrees C. Cellular metabolic functions and resorption of cultured fetal rat bones (release of 45Ca from pre-labeled long bone) were affected by A23187 in a biphasic manner: cell cyclic AMP (cAMP) was increased by 0.1 and 0.3 mug/ml of the ionophore, whereas 10 mug/ml was either ineffective or lowered the cAMP levels. The high A23187 concentration abolished the stimulatory effects of parathyroid hormone and methylisobutylxanthine. Concentrations of 0.1 and 0.3 mug/ml A23187 stimulated bone resorption. The effect was abolished by calcitonin. Ionophore concentrations above 1 mug/ml produced less bone resorption. These higher concentrations antagonized the bone-resorbing effect of parathyroid hormone and 1,25-dihydroxyvitamin D3. A23187 at 5 and 10 mug/ml decreased bone cell lactate and ATP. Thus at low concentrations, A23187 produced effects on bone similar to those of parathyroid hormone, suggesting that calcium is the primary initiator of PTH-induced bone resorption. At the higher concentrations A23187 may have a general inhibitory effect on cell metabolism.

Adenosine Triphosphate↗
PubMed1975

Cytoplasmic glucocorticoid binding proteins in bone cells.

The binding of 3H-dexamethasone (3H-DM) was studied in the cytoplasmic fraction of bone cells isolated from fetal rat calvaria by enzymatic digestion. An high-affinity glucocorticoid binding protein resembling those described in other target tissues was demonstrated. Scatchard analysis revealed a single class of binding sites with an apparent dissociation constant for 3H-DM (0C) of 7 x 10-9M and a concentration of binding sites of 0.11 pmoles/mg cytosol protein. The number of cytoplasmic binding sites per cell was calculated at 6,000 which is probably an underestimate due to occupancy of some sites by endogenous steroids. The binding sites appeared protein in nature since incubation with pronase destroyed 100% of the binding. Nuclear transfer was demonstrated in a reconstituted system utilizing bone cytosol as donor and liver nuclei as the acceptor. Competitive binding analysis revealed corticosterone to be equivalent to DM in binding affinity; progesterone was 75% as potent as DM. Aldosterone and SC-26304 (a spirolactone analogue) had, respectively, 1

17-Hydroxycorticosteroids↗
PubMed1975

Calcium transport in isolated bone cells. III. Effects of parathyroid hormone and cyclic 3',5'-AMP.

The effects of parathyroid hormone (PTH) and cyclic 3',5'-AMP (cyclic AMP) on calcium transport were studied in isolated bone cells. Bone cells were isolated by collagenase digestion of 20-21 day old fetal rat calvaria. Calcium transport was measured with 45Ca. PTH (0.2 mug/ml) increased calcium uptake 30--40% over control values at 37 C. At 4 C, the effects were magnified and 70--170% increases in calcium uptake were observed. The effects were present 1--10 minutes after the simultaneous addition of hormone and 45Ca. PTH had no effect on calcium efflux. Neither dibutyryl cyclic AMP (10(-4)-10(-3)M) nor cyclic AMP (10(-7)-3 X 10(-6)M) had any effect on calcium uptake or efflux. Methylisobutylxanthine (0.1 mM) caused no change in calcium uptake although increase in cyclic AMP were noted. The characteristic PTH-induced increase in cyclic AMP seen at 37 C was not observed at 4 C. It is postulated that PTH increases the permeability of bone cell membranes to calcium. At 4 C the membrane is relatively impermeable so the PTH effect is magnified. The PTH-induced increase does not appear to be mediated through cyclic AMP.

Animals↗