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M Lieberherr

Publications and source records attributed to M Lieberherr.

At least 37 records · Page 2Linked to original sources
PubMed1998

Effects of extracellular calcium on the proliferation and differentiation of porcine osteoblasts in vitro.

We examined the effects of various extracellular calcium concentrations on DNA content, procollagen type I carboxy-terminal propeptide (PICP) release (reflects type I collagen synthesis), and alkaline phosphatase activity of porcine osteoblasts. Osteoblasts seeded in control medium (2.2 mM calcium) were transferred to low (0. 5 or 1 mM) calcium medium or to high (3, 5, 7, or 10 mM) calcium medium at different stages of the culture period and for different incubation times. When osteoblasts were transferred to low or high (3 or 5 mM) calcium medium 1 or 2 days after plating and kept in that medium until the end of the culture period, PICP release was inhibited, but DNA content and alkaline phosphatase activity were unchanged, except in 5 mM calcium, which inhibited alkaline phosphatase activity. Short-term culture of subconfluent and near-confluent osteoblasts in 7 or 10 mM calcium for 48 h inhibited DNA content. DNA content returned to normal levels when cells were transferred back to control medium, whereas alkaline phosphatase inhibition induced by 5, 7, or 10 mM calcium was not reversible. Short-term culture in high calcium media did not affect PICP release. Thus, in porcine osteoblasts, low and high extracellular calcium concentrations affect DNA content, PICP release, and the expression of osteoblastic phenotype markers (alkaline phosphatase activity). These effects are dependent on the duration of calcium treatment and the state of differentiation of the osteoblasts.

Alkaline Phosphatase↗
PubMed1997

Phospholipase C beta and membrane action of calcitriol and estradiol.

We have shown that estrogens and calcitriol, the hormonally active form of vitamin D, increase the concentration of intracellular calcium ([Ca2+]i) within 5 s by mobilizing calcium from the endoplasmic reticulum and the formation of inositol 1,4, 5-trisphosphate and diacylglycerol. Because the activation of effectors as phospholipase C (PLC) coupled to G-proteins is the early event in the signal transduction pathway leading to the inositol 1,4,5-trisphosphate formation and to [Ca2+]i increase, we described different PLC isoforms (beta1, beta2, gamma1, and gamma2, but not beta4) in female rat osteoblasts using Western immunoblotting. The data showed that phospholipase C beta was involved in the mobilization of Ca2+ from the endoplasmic reticulum of Fura-2-loaded confluent osteoblasts by calcitriol and 17beta estradiol, and PLC gamma was ineffective. The data also showed that only a PLC beta1 linked to a Pertussis toxin-insensitive G-protein and a PLC beta2 coupled to a Pertussis toxin-sensitive G-protein are involved in the effects of calcitriol and 17beta estradiol on the mobilization of Ca2+ from intracellular Ca2+ stores. In conclusion, these results may be an important step toward understanding membrane effects of these steroids and may be an additional argument in favor of membrane receptors to steroid hormones.

4-Nitrophenylphosphatase↗
PubMed1997

Testosterone induces Ca2+ influx via non-genomic surface receptors in activated T cells.

Using the Fura-2 method we investigated a possible direct action of testosterone on cytosolic free calcium of splenic T cells isolated from female C57BL/10 mice. Testosterone at physiological concentrations of 1-10 nM induces an increase in [Ca2+]i within seconds, which is due to Ca2+ influx and not to Ca2+ release from intracellular stores. In contrast, estradiol induces both Ca2+ influx and Ca2+ release. The testosterone-induced Ca2+ influx is mediated by Ni2+-blockable channels and is not inhibited by cyproterone, a blocker of the classical androgen receptor. Ca2+ influx can also be induced by testosterone conjugated to BSA which is impermeable to the plasma membrane. These data indicate a novel mode of direct action of testosterone on T cells which is not mediated through the classical androgen receptor response, but through unconventional plasma membrane receptors.

Animals↗
PubMed1997

Different mechanisms are involved in intracellular calcium increase by insulin-like growth factors 1 and 2 in articular chondrocytes: voltage-gated calcium channels, and/or phospholipase C coupled to a pertussis-sensitive G-protein.

This study describes the mechanisms involved in the IGF-1 and IGF-2-induced increases in intracellular calcium concentration [Ca2+]i in cultured chondrocytes and the involvement of type 1 IGF receptors. It shows that IGF-1, IGF-2, and insulin increased the cytosolic free calcium concentration [Ca2+]i in a dose-dependent manner, with a plateau from 25 to 100 ng/ml for both IGF-1 and IGF-2 and from 1 to 2 micrograms/ml for insulin. The effect of IGF-1 was twice as great as the one of IGF-2, and the effect of insulin was 40% lower than IGF-1 effect. Two different mechanisms are involved in the intracellular [Ca2+]i increase. 1) IGF-1 and insulin but not IGF-2 involved a Ca2+ influx through voltage-gated calcium channels: pretreatment of the cells by EGTA and verapamil diminished the IGF-1 or insulin-induced [Ca2+]i but did not block the effect of IGF-2. 2) IGF-1, IGF-2, and insulin also induced a Ca2+ mobilization from the endoplasmic reticulum: phospholipase C (PLC) inhibitors, neomycin, or U-73122 partially blocked the intracellular [Ca2+]i increase induced by IGF-1 and insulin and totally inhibited the effect of IGF-2. This Ca2+ mobilization was pertussis toxin (PTX) dependent, suggesting an activation of a PLC coupled to a PTX-sensitive G-protein. Lastly, preincubation of the cells with IGF1 receptor antibodies diminished the IGF-1-induced Ca2+ spike and totally abolished the Ca2+ influx, but did not modify the effect of IGF-2. These results suggest that IGF-1 action on Ca2+ influx involves the IGF1 receptor, while part of IGF-1 and all of IGF-2 Ca2+ mobilization do not implicate this receptor.

Animals↗
PubMed1997

Nongenomic effects of an anti-idiotypic antibody as an estrogen mimetic in female human and rat osteoblasts.

We investigated the early effects of the anti-idiotypic antibody (clone 1D5), which recognized the estrogen receptor (ER), on cytosolic free calcium concentration ([Ca2+]i) and its long term effects on creatine kinase (CK) specific activity in female human and rat osteoblasts. These actions were compared to the known membrane and genomic effects of 17 beta estradiol (E2). Like E2, clone 1D5 increased within 5 s [Ca2+]i in both cell types by two mechanisms: 1) Ca2+ influx through voltage-gated Ca2+ channels as shown by using EGTA a chelator of extracellular Ca2+, and nifedipine, a Ca2+ channel blocker; 2) Ca2+ mobilization from the endoplasmic reticulum as shown by using phospholipase C inhibitors, such as neomycin and U-73122, which involved a Pertussis toxin-sensitive G-protein. Clone 1D5 and E2 stimulated CK specific activity in human and rat osteoblasts with ten fold higher concentrations than those needed for the membrane effects (0.1 microgram/ml and 10 pM, respectively). Both effects were gender-specific since testosterone and 5 alpha-dihydotesterone were uneffective. Tamoxifen and Raloxifene, two estrogen nuclear antagonists, inhibited CK response to 1D5 and E2 and Ca2+ response to 1D5, but not Ca2+ response to E2. By contrast, (Fab')2 dimer, a proteolytic fragment of 1D5 with antagonist properties, inhibited both membrane and genomic effects of 1D5 and E2. In conclusion, these results imply that clone 1D5 has an estrogen like activity both at the membrane and nuclear levels in female human and rat osteoblasts. 1D5 must therefore interact with membrane binding sites, penetrate the cells, and reach the nuclear receptors by an as yet uncharacterized mechanism.

Animals↗
PubMed1996

Progesterone triggers rapid transmembrane calcium influx and/or calcium mobilization from endoplasmic reticulum, via a pertussis-insensitive G-protein in granulosa cells in relation to luteinization process.

We investigated the early effects (5-60 s) of progesterone (1 pM-0.1 microM) on cytosolic free calcium concentration ([Ca2+]i) and inositol 1,4,5-trisphosphate (InsP3) formation in nonluteinized and in vitro luteinized porcine granulosa cells (pGCs). Progesterone increased [Ca2+]i and InsP3 formation within 5 s in both cell types. Progesterone induced calcium mobilization from the endoplasmic reticulum via the activation of a phospholipase C linked to a pertussis-insensitive G-protein. This process was controlled by protein kinases C and A. In contrast, only nonluteinized pGCs showed a Ca2+ influx via dihydropyridine-insensitive calcium channel. In both cell types, the nuclear progesterone receptor antagonist RU-38486 did not inhibit the progesterone-induced increase in [Ca2+]i, progesterone immobilized on bovine serum albumin, which did not enter the cell, increased [Ca2+]i within 5 s and was a full agonist, but less potent than the free progesterone; pertussis toxin did not inhibit progesterone effect on InsP3. In conclusion, progesterone may interact with membrane unconventional receptors that belong to the class of membrane receptors coupled to a phospholipase C via a pertussis toxin-insensitive G-protein. The source of the Ca2+ for the progesterone-induced increase in [Ca2+]i also depends on the stage of cell luteinization.

Animals↗
PubMed1994

Androgens increase intracellular calcium concentration and inositol 1,4,5-trisphosphate and diacylglycerol formation via a pertussis toxin-sensitive G-protein.

Bone is a target tissue of androgens, but the mechanisms by which they act on bone are still unclear. This study examines the early (5-60 s) effects of 1 pM to 1 microM testosterone on cytosolic free Ca2+ concentration ([Ca2+]i) and inositol 1,4,5-trisphosphate (InsP3) and diacyglycerol (DAG) formation in confluent male rat osteoblasts. 10 pM to 10 nM testosterone increased [Ca2+]i within 5 s via Ca2+ influx as shown by the effects of EGTA and the Ca2+ channel blockers nifedipine and verapamil and via Ca2+ mobilization from the endoplasmic reticulum as shown by the effects of thapsigargin and neomycin. 10 pM to 10 nM testosterone increased InsP3 and DAG formation within 10 s. Testosterone immobilized on bovine serum albumin (testosterone (O-carboxymethyl)oxime/bovine serum albumin) and its derivative, (O-carboxymethyl)oxime, rapidly increased [Ca2+]i and InsP3 and DAG formation and were full agonists, although they were less potent than the free steroid. Cyproterone acetate, a nuclear antagonist, did not block the increase in [Ca2+]i and InsP3 and DAG formation induced by testosterone. Finally, neomycin and pertussis toxin totally abolished the effects of testosterone on InsP3 and DAG. These results suggest that male rat osteoblasts bear nongenomic unconventional cell-surface receptors for testosterone that belong to the class of the membrane receptors coupled to a phospholipase C via a pertussis toxin-sensitive G-protein.

Androgens↗
PubMed1994

Cell stage-dependent effects of ascorbic acid on cultured porcine bone cells.

Pig bone cells were isolated from fetuses or young animals. In culture, they proliferated for 6 days, became confluent and began differentiating. The effects of ascorbic acid (AsA) on cell proliferation, alkaline phosphatase (ALP) activity, non-collagenous protein (NCP) and collagen synthesis, were studied by adding AsA to the medium at different times during culture. AsA affected fetal and post-natal cells similarly: ALP activity, NCP and collagen synthesis were markedly reduced in cells treated before confluence, but were strongly and dose-dependently stimulated in cells treated after confluence. AsA also stimulated cell proliferation. The cell stage-dependent action of AsA suggests that it may interfere with differentiation. The effects of AsA on ALP activity and DNA content were not coupled to its effect on collagen synthesis, raising the question of whether AsA action is matrix-mediated.

Alkaline Phosphatase↗
PubMed1994

Effects of lipoxygenase products of arachidonate metabolism on parathyroid hormone secretion.

High extracellular Ca2+ (Ca2+ ec) stimulates the formation of inositol phosphates and diacylglycerol and activates phospholipase A2 in porcine parathyroid cells. Ca2+ ec action is also coupled to the formation of arachidonic acid, the precursor of both the cyclooxygenase and lipoxygenase (LO) pathways. We previously reported that LO pathway products might act as second messengers and play a part in regulating PTH secretion by Ca2+ ec. We have now investigated the effects of hydroxyeicosatetranoic acids (HETEs) on PTH secretion. Collagenase-dispersed porcine parathyroid cells were incubated in low [Ca2+] (0.5 mM, maximal stimulation) with or without HETEs for three 15-min periods. 12- and 15-HETEs inhibited PTH secretion in a dose-dependent manner from 10(-12) to 10(-9) M. Maximal inhibition was with 10(-9) M. Since 12- and 15-HETEs are the metabolic reduction products of 12- and 15-HPETEs, we also examined the effect of those precursors on PTH release. 12- and 15-hydroxyperoxyeicosatetranoic acids (HPETEs) were more potent inhibitors of PTH secretion. The threshold concentrations of both HPETEs that inhibited PTH release were lower than those for HETEs: 10(-9) M suppressed PTH secretion. This effect is comparable to that of high [Ca2+] (2 mM). This provides new evidence that products of 12-LO and 15-LO pathways are potent inhibitors of PTH secretion.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1994

Effects of growth hormone and insulin-like growth factor-I on the proliferation and differentiation of cultured pig bone cells and rat calvaria cells.

Growth hormone (GH) increases bone formation in vivo in pigs. The capacity of GH and its mediator insulin-like growth factor-I (IGF-I) to influence bone cell proliferation and differentiation was investigated in cells isolated from trabecular and cortical bone of growing pigs, from fetal pig bone and from newborn rat calvaria. GH enhanced the proliferation of confluent rat cells but did not affect that of either confluent or subconfluent porcine cells from trabecular, cortical or fetal bone. IGF-I increased the proliferation of confluent rat cells and subconfluent pig cells. GH slightly inhibited alkaline phosphatase (ALP) activity in pig cells of the three origins while IGF-I increased it in cortical cells. Collagen synthesis by pig cells was stimulated by IGF-I but not by GH. These results suggest that GH does not stimulate bone forming cells in pigs, and that GH and IGF-I affect cultured bone cells differently depending on the species or bone type they were isolated from.

Alkaline Phosphatase↗
PubMed1993

Oscillations in inositol 1,4,5-trisphosphate and diacyglycerol induced by vitamin D3 metabolites in confluent mouse osteoblasts.

For the last 5 years, attention has focused on the nongenomic effects of 1,25-(OH)2D3, but considerably less is known about the mechanisms of the nonnuclear actions of 24,25-(OH)2D3. The present study examines and compares the rapid (5-90 s) effects of 100 pM to 10 nM 24,25-(OH)2D3, 10 pM to 1 nM 1,25-(OH)2D3, and 1-100 nM 25-OHD3 on the formation of inositol phosphates and lipids in confluent mouse osteoblasts. 24,25-(OH)2D3 and 25-OHD3 effects were dose dependent; those of 1,25-(OH)2D3 were dose dependent in a bell-shaped manner. The two dihydroxylated metabolites induced a multiphasic response in inositol 1,4,5-trisphosphate (IP3) formation with three stimulation peaks; the IP3 response to 25-OHD3 was monophasic. The amplitude of the IP3 response to 24,25-(OH)2D3 was greater and its oscillation period was slower than that induced by 1,25-(OH)2D3. The diacylglycerol (DAG) responses to secosteroids showed two stimulation peaks that appeared at different times depending on the secosteroid used. Pretreatment with neomycin totally inhibited the first DAG response; neomycin had no effect on the second peak of DAG induced by 25-OHD3, whereas it partially blocked the second response of DAG to 24,25-(OH)2D3 and 1,25-(OH)2D3. These data show for the first time that 24,25-(OH)2D3 can modulate phospholipid metabolism in confluent mouse osteoblasts as early as 5-10 s. The first pathway used by all three secosteroids is that of the hydrolysis of phosphatidylinositol 4,5-bisphosphate via phospholipase C activation, leading to the formation of the two second messengers, IP3 and DAG, since neomycin totally blocked the response. Thus, the action of these secosteroids on the osteoblast membrane may also implicate several steps of the phosphatidylcholine cycle, according to the metabolite tested. Finally, these data point to a direct interaction of vitamin D metabolites with specific membrane recognition moieties.

24,25-Dihydroxyvitamin D 3↗
PubMed1993

Cell signaling and estrogens in female rat osteoblasts: a possible involvement of unconventional nonnuclear receptors.

Estrogen deficiency is associated with bone loss, and estrogen replacement is an effective treatment of this osteoporotic process. This study examines the early (5-120 s) effects of 17 beta-estradiol on the intracellular calcium and phospholipid metabolism in confluent female rat osteoblasts. The cytosolic free Ca2+ concentration ([Ca2+]i) was determined using fura-2/AM as Ca2+ probe. Cells were labeled with myo-[2-3H]inositol or [14C]arachidonic acid for inositol or lipid determination. Inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG) production were determined by either mass measurement or anion-exchange chromatography or by thin-layer chromatography, respectively. 17 beta-Estradiol (1 pM to 1 nM) increased [Ca2+]i in a biphasic manner within 10 s via Ca2+ influx from the extracellular milieu, as shown by the effects of the calcium chelator EGTA and the Ca2+ channel blockers nifedipine and verapamil, and via Ca2+ mobilization from the endoplasmic reticulum (ER), as shown by the effects of thapsigargin. 17 beta-Estradiol (1 pM to 1 nM) induced a biphasic and concomitant increase in IP3 and DAG formation. Estradiol immobilized on bovine serum albumin (BSA) [E-(O-carboxymethyl)oxime BSA] and its derivative (O-carboxymethyl)oxime rapidly increased ([Ca2+]i, IP3, and DAG and were full agonists, although they were less potent than the free estradiol. They had the same action time course and acted via Ca2+ influx and Ca2+ mobilization from ER. Tamoxifen, a potent inhibitor of genomic steroid responses, did not block the rapid increase in Ca2+, IP3, and DAG induced by estradiol. Finally, inhibitor of phospholipase C (neomycin) and pertussis toxin abolished the effects of 17 beta-estradiol on IP3 and DAG formation. These results suggest that female rat osteoblasts bear non-genomic unconventional cell surface receptors for estradiol, belonging to the class of the membrane receptors coupled to a phospholipase C via a pertussis toxin-sensitive G protein.

Animals↗
PubMed1992

Phospholipase-A2 action and arachidonic acid metabolism in calcium-mediated parathyroid hormone secretion.

The involvement of arachidonic acid (AA) and its metabolites in the control of PTH secretion by porcine parathyroid cells was investigated. Increasing the extracellular calcium concentration from 0.5 to 2 mM increased free [3H]AA release and decreased PTH secretion from labeled parathyroid cells as a function of time (1-30 min). Free [3H]AA in the medium was significantly increased (+153 +/- 6%) after 5 min, while PTH secretion was significantly decreased (-75 +/- 7%) only after 15 min, suggesting a link between the two. [3H]AA release was associated with a decrease in [3H]AA incorporated into phosphatidylinositol, phosphatidic acid, and phosphatidylcholine, suggesting that these phospholipids are the major source of AA. Exogenous phospholipase-A2 (PL-A2; 1-500 mU/ml) and AA (5-40 microM) inhibited PTH secretion in a dose-dependent manner. PTH secretion inhibited by 2 mM Ca2+ was restored by two PL-A2 inhibitors, indomethacin (30 microM) and mepacrine (50 microM). The cyclooxygenase pathway inhibitor ibuprofen (20 microM) did not restore PTH secretion of affect high Ca(2+)-, AA-, or PL-A2-inhibited PTH secretion. Two inhibitors of the lipoxygenase pathway (LO), phenidone (1 microM) and baicalein (0.1 microM), a relatively selective 12-LO inhibitor, blunted high Ca(2+)-induced inhibition of PTH secretion (+101 +/- 10% and +105 +/- 6%, respectively), but nordihydroguaiaretic acid, which inhibits the 5-LO pathway, did not restore PTH secretion inhibited by high Ca2+, AA, or PL-A2. These results suggested that AA and agents that cause its liberation inhibit PTH secretion. AA may act via the 12-LO, but not via the 5-LO or cyclooxygenase, pathway. Thus, 12-LO products may be second messengers in parathyroid cells.

Acetophenones↗
PubMed1990

Rapid effects of 1,25-dihydroxyvitamin D3 and extracellular Ca2+ on phospholipid metabolism in dispersed porcine parathyroid cells.

We examined the rapid effects (less than 120 sec) of 1,25(OH)2D3 on membrane phospholipid hydrolysis in porcine parathyroid cells and compared these effects to those produced by extracellular Ca2+. Cells were labeled with [3H]myo-inositol or [14C]arachidonic acid for 3 h, then exposed to various 1,25(OH)2D3 concentrations in 0.5 mM Ca2+ for different time periods or to 2 mM [Ca2+]. Parathyroid cells showed a biphasic increase in diacylglycerol (DAG), monoacylglycerol (MG), phosphatidic acid (PA), and inositol trisphosphate (IP3) in response to 1,25(OH)2D3 (10(-12)-10(-8) M) or to 2 mM [Ca2+]. This effect was rapid (within 5 sec) and dose-dependent, with a maximal stimulation with 10 pM of 1,25(OH)2D3. At this concentration, the first peak of DAG, MG, and IP3 was at 5 sec and reached 176 +/- 9%, 134 +/- 4%, and 154 +/- 13%, respectively vs. basal levels. For PA, the first maximum increase was at 20 sec (130 +/- 6%). At 30 sec MG, PA, and IP3 returned to basal levels, whereas the decrease in DAG was under the basal level (-25 +/- 5%). The second peak reached a maximum at 60 sec for the four products (145 +/- 8%, 119 +/- 5%, 125 +/- 6%, and 175 +/- 20%, respectively) then decreased to basal level at 120 sec. High extracellular Ca2+ (2 mM) and fluoride (5 mM) also produced similar increase in phosphatidylinositol metabolites, except that DAG levels returned to basal level at 30 sec. In conclusion, the present data shows the existence of rapid effects of 1,25(OH)2D3 in porcine parathyroid cells. The short time sequence suggests that they are mediated by a direct interaction with the membrane, possibly through a receptor-mediated process linked to phospholipase C by a G-protein.

Animals↗
PubMed1989

A functional cell surface type receptor is required for the early action of 1,25-dihydroxyvitamin D3 on the phosphoinositide metabolism in rat enterocytes.

1,25-Dihydroxyvitamin D3 (1,25-(OH)2-D3) (0.1 pM to 2 nM) induces a concomitant very rapid (within 5 s) and transient release of inositol trisphosphate and diacylglycerol in enterocytes from 3-month-old rats. This high level is not maintained but declines to a lower level 60 s after stimulation. The stimulating effect is dose-dependent and biphasic with a maximum effect at 10 pM. 1,25-(OH)2-D3 induces a rapid (within 10 s) accumulation of inositol bisphosphate and its effect on inositol monophosphate is delayed (120 s). The primary action of 1,25-(OH)2-D3 is to initiate hydrolysis of phosphatidyl 4,5-bisphosphate to yield inositol trisphosphate and diacylglycerol. In contrast, 1,25-(OH)2-D3, for any of the concentrations and the incubation time periods tested, has no effect on inositol trisphosphate and diacylglycerol formation in enterocytes from 16-day-old rats at a time when specific binding sites for 1,25-(OH)2-D3 cannot be detected. In conclusion, the early (within 5-60 s) effects of 1,25-(OH)2-D3 on small intestinal epithelium may be mediated via the phosphoinositide transduction system and require the presence of functioning cell membrane-type receptors.

Animals↗
PubMed1987

Effects of vitamin D3 metabolites on cytosolic free calcium in confluent mouse osteoblasts.

A fluorescent Ca2+ indicator, acetoxymethyl Quin2, was used to quantify changes in the cytosolic free calcium concentration ([Ca2+]i) of confluent mouse osteoblasts. 1,25 - Dihydroxycholecalciferol (1,25 - (OH)2D3, 10-100 pM), 25-hydroxycholecalciferol (25-(OH)D3, 10-100 nM), parathyroid hormone (PTH(1-84), 0.1-10 nM), and prostaglandin E2 (PGE2, 10-1000 nM) all induced immediate (t less than 15 s) transient increases in [Ca2+]i, from a basal level of 135 +/- 8 nM to levels of 179-224 nM. These increases rapidly returned to a plateau approximately 10% higher than the basal level. 24,25-Dihydroxycholecalciferol (24,25-(OH)2D2, 0.1-10 nM) induced a rapid increase in [Ca2+]i which remained elevated for 5 min before decreasing. The 1,25-(OH)2D3- and PTH-induced spikes were abolished by the prior addition of EGTA and Ca2+ entry blockers (verapamil, nifedipine, 1 microM) while the responses to 25-(OH)D3, 24,25-(OH)2D3, and PGE2 were unaffected. Addition of 1,25-(OH)2D3 + EGTA or PTH + EGTA caused enhanced Ca efflux. Addition of drugs which interfere with calcium sequestration by the endoplasmic reticulum (ER) (caffeine, 4 mM; 8-(diethyl-amino)-octyl 3,4,5-trimethoxybenzoate HCl, 0.5 mM) or mitochondria (antimycin, 10 microM; oligomycin, 5 microM) showed that 25-(OH)D3 and PGE2 mainly mobilized Ca2+ from ER. 1,25-(OH)2D3 and bovine PTH caused a transient increase in [Ca2+]i, 70% of which resulted from Ca2+ influx from outside the cells and 30% by release from the ER. The [Ca2+]i increase induced by 24,25-(OH)2D3 included a 30% contribution from the ER and 70% from the mitochondria.

Aminoquinolines↗
PubMed1987

Bone modeling in gallium nitrate-treated rats.

Gallium nitrate (GaN) reduces cancer-related hypercalcemia and inhibits bone resorption in vitro. This study investigated the effects of chronic GaN administration on bone, kidney, and parathyroid gland activity of growing rats. Experimental animals received GaN (1.75 mg elemental gallium i.p. QOD X 8, Ga+), and controls received the solvent (Ga-). In the bone of Ga+ rats the number of osteoclasts was increased (Ga+: 70.4 +/- 2.31 osteoclasts/mm2; Ga-: 46.5 +/- 1.61 osteoclasts/mm2, P less than 0.001), and apposition rate and osteoid width were unchanged. Ga was concentrated in bone (2.4 mumol/g cortical bone) and detected by electron microprobe on the surface of a few trabeculae. Alkaline (Alp) and acid (Acp) phosphatase activities were higher in Ga+ than in Ga- calvaria (Ga+: Alp 223 +/- 23.4 U/mg prot, Ga-: Alp 145 +/- 13.3 U/mg prot, P less than 0.02; Ga+: Acp 69.5 +/- 4.7 U/mg prot, Ga-: 57.5 +/- 2.8 U/mg prot, P less than 0.05). Serum iPTH was increased (Ga+: 112.9 +/- 17.6 pg/ml, Ga-: 41.4 +/- 7.4 pg/ml, P less than 0.01), serum calcium was reduced (Ga+: 2.4 +/- 0.02 mmol/l, Ga-: 2.6 +/- 0.03 mmol/l, P less than 0.001); calciuria remained comparable to controls. Relative to the hypocalcemia this suggests renal loss of Ca. The calcemic response to hPTH 1-34 (i.v. 50 micrograms/kg) was decreased 2 hours after injection of the hormone (delta Ca: TPTX Ga+: 0.11 +/- 0.04 mmol/l, Ga-: 0.33 +/- 0.03 mmol/l P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Acid Phosphatase↗