Bone resorbing activity and cytokine levels in gingival crevicular fluid before and after treatment of periodontal disease

BACKGROUND

The aim of the present study was to investigate bone resorption activity (BRA), interleukin-1 alpha (IL-1 alpha), IL-1 beta and interleukin-1 receptor antagonist (IL-1ra) in gingival crevicular fluid (GCF) in sites with no signs of periodontal disease and in sites with horizontal or angular loss of periodontal bone. These assessments were performed before and after periodontal treatment.

METHODS

GCFs were collected from 10 individuals with filter strips from two healthy sites and four sites with deep pathological periodontal pockets, two of which showed horizontal bone loss and two with angular bone loss. All diseased pockets were treated with flap surgery and systemic Doxyferm. Twelve months later GCF was collected again and treatment outcome evaluated. BRA in GCFs was assessed in a bone organ culture system by following the release of (45)Ca from neonatal mouse calvariae. The amounts of IL-1 alpha, IL-1 beta and IL-1ra in GCFs were quantified by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Treatment resulted in reduction of pocket depths with 3.5+/-0.5 mm in sites with angular bone loss and 2.8+/-0.3 mm in sites with horizontal bone loss. Initially, BRA, IL-1 alpha, IL-1 beta and IL-1ra were significantly higher in GCFs from diseased sites compared with healthy sites. No differences in BRA and cytokine levels were seen between GCFs from pockets with horizontal and angular bone losses. The levels of IL-1 alpha, IL-1 beta and IL-1ra were significantly reduced after treatment of diseased pockets. Pocket depths were significantly correlated to BRA only in pre-treatment sites with angular bone loss. BRA was correlated to Il-1 alpha, IL-1 beta, but not to IL-1ra, in diseased sites with angular bone loss, before and after treatment. The reductions of BRA in the individual sites, seen after treatment, were not correlated to the reductions of Il-1 alpha, IL-1 beta or IL-1ra.

CONCLUSIONS

These data show that BRA and cytokine levels are increased in GCFs from sites with periodontal disease and that periodontal treatment results in reduction of the cytokines. Our findings further indicate that IL-1 alpha and IL-1 beta play important roles for the BRA present in GCFs, but that other factors also contribute to this activity.

In vitro microleakage of four tracers with multiple applications to the same tooth

Microleakage testing continues to be undertaken using a variety of techniques and methodologies. This study compared four microleakage tracers to determine if a difference exists in their ability to demonstrate microleakage on a single dental amalgam restorative material by testing in two phases. Class V amalgam restorations were placed on the facial surfaces of 105 extracted human premolars with all margins in enamel. The teeth were stored at 37 degrees C in water for two weeks except during thermocycling for 2500 cycles between 8 degrees C and 48 degrees C. The teeth were prepared for microleakage testing by sealing the external surfaces with nail polish and tinfoil, leaving the restoration and surrounding 1 mm exposed. In the first phase, four groups of 15 teeth were randomly assigned to 0.5% basic fuchsin dye, 2.0% fluorescent dye, 1.5% reactive orange 14 and 45Ca. In the second phase, another three groups of 15 teeth were immersed in 45Ca, then immersed in one of the remaining three tracers. Ridit analysis and Newman-Keuls multiple comparisons were used to compare the groups at a significance level of 0.05. The results indicate that there are differences in observed microleakage between tracers and there is no statistical influence on dye tracers by initial immersion in 45Ca.

Effects of selective prostaglandin EP2 and EP4 receptor agonists on bone resorption and formation in fetal rat organ cultures

Prostaglandin E2 (PGE2) can stimulate bone resorption and formation through receptors which activate adenylyl cyclase. We examined the effects of selective EP2 and EP4 agonists (EP2A and EP4A) on the release of previously incorporated 45Ca from fetal rat long bones and the incorporation of [3H]-proline or [3H]-thymidine (TdR) in fetal rat calvaria to assess the relative effects of these selective agonists on bone formation and resorption. Only EP4A was effective in increasing 45Ca release. Both agonists increased [3H]-TdR incorporation and [3H]-proline incorporation into calvariae, particularly in the presence of cortisol.

Voltage-dependent ebselen and diorganochalcogenides inhibition of 45Ca2+ influx into brain synaptosomes

By mediating the Ca(2+) influx, Ca(2+) channels play a central role in neurotransmission. Chemical agents that potentially interfere with Ca(2+) homeostasis are potential toxic agents. In the present investigation, changes in Ca(2+) influx into synaptosomes by organic forms of selenium and tellurium were examined under nondepolarizing and depolarizing conditions induced by high KCl concentration (135 mM) or by 4-aminopyridine (4-AP). Under nondepolarizing conditions, ebselen (400 micro M) increased Ca(2+) influx; diphenyl ditelluride (40-400 micro M) decreased Ca(2+) in all concentrations tested; and diphenyl diselenide decreased Ca(2+) influx at 40 and 100 micro M, but had no effect at 400 micro M. In the presence of KCl as depolarizing agent, ebselen and diphenyl ditelluride decreased Ca(2+) influx in a linear fashion. In contrast, diphenyl diselenide did not modify Ca(2+) influx into isolated nerve terminals. In the presence of 4-AP (3 mM) as depolarizing agent, ebselen (400 micro M) caused a significant increase, whereas diphenyl diselenide and diphenyl ditelluride inhibited Ca(2+) influx into synaptosomes. The results can be explained by the fact that the mechanism through which 4-AP and high K(+) induced elevation of intracellular Ca(2+) is not exactly coincident. The mechanism by which diphenyl ditelluride and ebselen interact with Ca(2+) channel is unknown, but may be related to reactivity with critical sulfhydryl groups in the protein complex. The results of the present study indicate that the effects of organochalcogenides were rather complex depending on the condition and the depolarizing agent used.

Cortisol rapidly suppresses intracellular calcium and voltage-gated calcium channel activity in prolactin cells of the tilapia (Oreochromis mossambicus)

Cortisol was previously shown to rapidly (10-20 min) reduce the release of prolactin (PRL) from pituitary glands of tilapia (Oreochromis mossambicus). This inhibition of PRL release by cortisol is accompanied by rapid reductions in (45)Ca(2+) and cAMP accumulation. Cortisol's early actions occur through a protein synthesis-independent pathway and are mimicked by a membrane-impermeable analog. The signaling pathway that mediates rapid, nongenomic membrane effects of glucocorticoids is poorly understood. Using the advantageous characteristics of the teleost pituitary gland from which a nearly pure population of PRL cells can be isolated and incubated in defined medium, we examined whether cortisol rapidly reduces intracellular free calcium (Ca(i)(2+)) and suppresses L-type voltage-gated ion channel activity in events that lead to reduced PRL release. Microspectrofluorometry, used in combination with the Ca(2+)-sensitive dye fura 2 revealed that cortisol reversibly reduces basal and hyposmotically induced Ca(i)(2+) within seconds (P < 0.001) in dispersed pituitary cells. Somatostatin, a peptide known to inhibit PRL release through a membrane receptor-coupled mechanism, similarly reduces Ca(i)(2+). Under depolarizing [K(+)], the L-type calcium channel agonist BAY K 8644, a factor known to delay the closing of L-type Ca(2+) channels, stimulates PRL release in a concentration-dependent fashion (P < 0.01). Cortisol (and somatostatin) blocks BAY K 8644-induced PRL release (P < 0.01; 30 min), well within the time course over which its actions occur, independent of protein synthesis and at the level of the plasma membrane. Results indicate that cortisol inhibits tilapia PRL release through rapid reductions in Ca(i)(2+) that likely involve an attenuation of Ca(2+) entry through L-type voltage-gated Ca(2+) channels. These results provide further evidence that glucocorticoids rapidly modulate hormone secretion via a membrane-associated mechanism similar to that observed with the fast effects of peptides and neurotransmitters.

Intestinal bicarbonate secretion in marine teleost fish-source of bicarbonate, pH sensitivity, and consequences for whole animal acid-base and calcium homeostasis

Whole animal studies using seawater European flounder (Platichthys flesus) revealed that increasing intestinal [Ca(2+)] to 20 mM stimulated net HCO(3)(-) base secretion by 57%, but this was effectively balanced by an increase in net acid secretion, likely from the gills, to maintain whole animal acid-base status. Higher Ca(2+) concentrations (40 and 70 mM) in ambient seawater resulted in reduced plasma total CO(2). This indicates (1) imperfect acid-base compensation, and (2) that endogenous metabolic CO(2) is insufficient to fuel intestinal HCO(3)(-) secretion, under hyper-stimulated conditions. Bicarbonate secretion plays an important role in preventing calcium absorption by precipitating a large fraction of the imbibed calcium as CaCO(3). Indeed, under high Ca(2+) conditions (20 mM), up to 75% of the intestinal Ca(2+) is precipitated as CaCO(3) and then excreted. This is undoubtedly important in protecting the marine teleost kidney from the need for excessive calcium excretion and risk of renal stone formation. Using an in vitro pH-stat technique with the isolated intestinal epithelium, the replacement of serosal CO(2) with a HEPES buffered saline had no effect on HCO(3)(-) secretion, indicating that the endogenous supply of HCO(3)(-) from CO(2) hydration within epithelial cells is adequate for driving baseline secretion rates. Further, in vitro data demonstrated a stimulatory effect of low pH on intestinal HCO(3)(-) secretion. Thus, both luminal Ca(2+) and H(+) can regulate HCO(3)(-) secretion but the precise mechanisms and their potential interaction are currently unresolved.

Epidermal growth factor regulates Ca2+ uptake in primary cultured renal proximal tubule cells: involvement of cAMP, PKC and cPLA2

Epidermal growth factor (EGF) is known to play an important role in modulating renal transport functions. Thus, we investigated the effect of EGF on Ca(2+) uptake and its related signals in the primary cultured rabbit renal proximal tubule cells. EGF (50 ng/ml, 1 h) stimulated Ca(2+) uptake. Its effect was blocked by AG 1478 (an EGF receptor antagonist), genistein or herbimycin A (tyrosine kinase inhibitors). EGF increased intracellular cAMP level and SQ 22536 (an adenylate cyclase inhibitor), Rp-cAMP (a cAMP analogue), or PKI (a protein kinase A inhibitor) blocked the EGF-induced stimulation of Ca(2+) uptake. EGF-induced stimulation of Ca(2+) uptake was also blocked by neomycin or U-73122 (phospholipase C inhibitors), staurosporine, H-7, or bisindolylmaleimide I (protein kinase C inhibitors), nifedipine or methoxyverapamil (L-type Ca(2+) channel blockers). It increased IPs formation by 167 +/- 5% compare to control within 90 s. On the other hand, EGF increased [(3)H]-arachidonic acid release, which was significantly blocked by PKC inhibitors. In addition, PGE(2), one of cyclooxygenase metabolites, and 5,6-EET, one of cytochrome P-450 metabolites, increased Ca(2+) uptake. These results suggest that cAMP, PLC/PKC, and PLA(2) are involved in EGF-induced stimulation of Ca(2+) uptake.

Homocysteine potentiates calcification of cultured rat aortic smooth muscle cells

Aortic calcification was demonstrated in experimental animal models of hyperhomocysteinemia. Mild hyperhomocysteinemia was associated with aortic calcification, suggesting a relationship between homocysteine (HCY) and the pathogenesis of aortic calcification. In the present study, the effect of HCY on vascular calcification was examined in calcifying and non-calcifying vascular smooth muscle cells (VSMCs). Cell calcification was induced by incubation of VSMCs with beta-glycerophosphate. Proliferation of VSMCs was studied by cell counting, 3H-thymidine (3H-TdR) and 3H-leucine (3H-Leu) incorporation. 45Ca accumulation, cell calcium content, and alkaline phosphatase (ALP) activity were measured as indices of calcification. The results showed that the proliferation of calcifying VSMCs, which was indicated by cell counting, 3H-TdR and 3H-Leu incorporation in calcifying VSMCs, was enhanced as compared with that of non-calcifying VSMCs. HCY promoted increases in cell number, 3H-TdR and 3H-Leu incorporation in both calcifying and non-calcifying VSMCs, but with more prominent effect in calcifying VSMCs. The stimulating effects of HCY on the three parameters in calcifying VSMCs were antagonized by PD98059, a specific inhibitor of mitogen activated protein kinase kinase (MAPKK). The ALP activity, 45Ca uptake, and calcium deposition in the calcifying VSMCs were greater than those in non-calcifying VSMCs. PD98059 had no effect on ALP activity, 45Ca uptake, and calcium deposition in calcifying VSMCs. HCY caused marked increases in 45Ca uptake and calcium deposition both in calcifying and non-calcifying VSMCs. HCY, however, enhanced ALP activity in the calcified VSMCs but not in the non-calcifying VSMCs. The non-calcifying VSMCs treated with HCY showed the same low ALP activity, as did the control VSMCs. In calcifying VSMCs, the HCY-induced increases in 45Ca uptake, calcium deposition, and ALP activity were also attenuated by PD98059. The results demonstrated that HCY potentiated VSMC calcification probably through the mechanisms by which HCY promotes atherosclerosis.

Kinetic analyses of waterborne Ca and Cd transport and their interactions in the gills of rainbow trout (Oncorhynchus mykiss) and yellow perch (Perca flavescens), two species differing greatly in acute waterborne Cd sensitivity

We evaluated the differential nature of interactions between waterborne Ca and Cd transport in the gills of yellow perch (Perca flavescens) and rainbow trout (Oncorhynchus mykiss), two species with a more than 400-fold difference in acute waterborne Cd tolerance. The Jmax (maximum rate of uptake) and K(m) (inverse of affinity) for Ca uptake, in the absence of Cd, were significantly lower in yellow perch (120.48 nM g(-1) wet wt h(-1) and 92.17 microM, respectively) relative to rainbow trout (188.68 nM g(-1) wet wt h(-1) and 243.90 microM, respectively). Similarly, the Jmax for Cd uptake, at the lowest waterborne Ca level (100 microM) tested, was significantly lower in yellow perch (0.27 nM g(-1) wet wt h(-1)) relative to rainbow trout (0.40 nM g(-1) wet wt h(-1), but no significant difference was observed in the K(m) values between the two species (yellow perch: 32.47 nM; rainbow trout: 31.27 nM). Waterborne Cd (0-890 nM) as well as waterborne Ca (100-1,000 microM) competitively inhibited branchial uptake of each other in both species. However, analyses of inhibitor constants for branchial Ca uptake by waterborne Cd (Ki[Cd2+]) revealed that the inhibition was about 1.8 times more potent in rainbow trout compared to yellow perch. In contrast, analyses of inhibitor constants for branchial Cd uptake by waterborne Ca (Ki[Cd2+]) indicated that the inhibition was more than three fold more potent in yellow perch than in rainbow trout. Higher branchial Ca uptake and more potent inhibition by Cd as well as higher branchial Cd uptake and less potent inhibition by Ca were also reflected in whole-body measurements of Ca and Cd influx in trout relative to perch. Overall, whole-body effects were in accord with the branchial kinetic analyses. These results further strengthen the conclusion that branchial influxes of Ca and Cd occur through common pathways. Moreover, interspecific differences in acute waterborne Cd sensitivity can be explained, at least in part, by the differential nature of interactions between waterborne Ca and Cd transport in fish gills.

Dentin matrix protein 1 initiates hydroxyapatite formation in vitro

Bone and dentin formation are interesting examples of matrix-mediated mineralization. However, factors and mechanisms regulating this process are poorly understood. Dentin matrix protein 1 (DMP1) is an acidic extracellular matrix protein found in dentin and bone, and based on its amino acid composition it could be postulated to play an important role in mineralization. Our present study examines the ability of recombinant DMP1 to initiate apatite formation in vitro. A 45Ca-binding assay demonstrated that recombinant DMP1 (rDMP1) possesses calcium-binding ability under physiological conditions. The in vitro nucleation experiments when conducted with rDMP1-coated glass plates demonstrated hydroxyapatite nucleation, while amorphous mineral was deposited on blank or BSA-coated surface. This mineral deposition was found to be 10-fold higher on rDMP1-coated glass surface when compared with the control glass plates. These findings suggest that DMP1 could be considered as a nucleator for apatite deposition in vitro.

[Study of age-specific changes in labeled citrate metabolism in health and disease]

A new coefficient - mineralized tissues/biological fluids (MT/BF) - is suggested for evaluating the distribution of compounds adsorbed by MT and dissolved in BF. The relative radioactivity (RRA) was estimated for the periods of 10 min to 96 h after intraperitoneal injection of [3-(14)C]citrate to rats aged 1 and 3 months and over 1 year by dividing the percent of incorporation in MT by the percent of incorporation in BF. Changes in RRA for molar root/blood serum (R/BS) and RRA for dentin/blood serum (D/BS) are similar: low values at the beginning of experiment, an increase 1 h postinjection, a decrease 2-3 h postinjection, and another increase (65-80 times) by 96 h postinjection. A biphasic reaction with a rapid elevation and decrease after 1-2 h and a second elevation before the end of the experiment due to citrate adsorption on hydroxyapatite and influence of D and R proteins on stable hemosorption of citrate by MT was observed. The time course of RRA enamel/oral fluid was different: a decrease 1 h postinjection and an increase 2-3 h postinjection. Two weeks after crossing the inferior alveolar nerve, the R/BS RRA decreased to a lesser degree in 1-month-old rats in comparison with 3-month-old animals, which can be explained by higher efficiency of the adaptive-compensatory mechanisms in growing rats.

Hydrothermal treatment and malting of barley improved zinc absorption but not calcium absorption in humans

OBJECTIVE

To study whether hydrothermal treatment or malting of barley (cv. Blenheim) improves zinc and calcium absorption in humans.

DESIGN

: Two groups of 10 and 12 healthy subjects, respectively, were in a period of 2 months in a fasting state, served two single meals each containing porridge or breakfast cereals prepared from processed or unprocessed (control) barley (60 g). The meals included 200 g of milk, extrinsically labelled with (65)Zn and (47)Ca. Whole-body retention of both minerals was measured.

SETTING

The study was carried out at the Department of Radiation Physics, Sahlgrenska University Hospital, Göteborg.

SUBJECTS

The subjects were recruited among students at the Göteborg University. None dropped out.

INTERVENTIONS

The activities of (65)Zn and (47)Ca were measured by whole-body counting four to five times over a 4-week period after each meal.

RESULTS

Zinc absorption from hydrothermally treated barley porridge, containing 28 mg P as inositol tri- to hexaphosphates (InsP(3)-InsP(6)), was significantly higher (P<0.001) than from control porridge containing 111 mg P as InsP(3)-InsP(6), 25.2+/-6.9 vs 11.0+/-2.5% (n=12). Calcium absorption did not differ (P>0.05), 21.1+/-6.8 vs 19.5+/-4.7% (n=12). Zinc absorption from breakfast cereals of malted barley with phytase activity and containing 70 mg P as InsP(3)-InsP(6,) was significantly higher (P<0.05) than from flakes of barley, containing 108 mg P as InsP(3)- InsP(6) and no phytase activity, 22.9+/-5.8 vs 14.8+/-4.6% (n=10). The calcium absorption was 21.3+/-6.5 vs 18.5+/-4.3% (n=10) and did not differ significantly (P>0.05).

CONCLUSION

Improvements of zinc absorption in breakfast meals can be achieved by optimised hydrothermal treatment or malting of barley. Calcium absorption was not influenced in the meals in this study.

SPONSORSHIP

Supported by Semper AB, Sweden, Oy Lahden Polttimo, Finland, the SL-Foundation, Sweden, Swedish National Board for Industrial and Technical Development (NUTEK), the Nordic Industrial Foundation, Swedish Council for Forestry and Agricultural Research (SJFR, project no 50.0306/97).

Calcium channels are present in the apical plasma membranes of the hepatopancreatic B-cells of Marsupenaeus japonicus

This study demonstrates the existence of calcium channels in the apical membranes of the hepatopancreatic blister (B) cells of Marsupenaeus japonicus. Using brush-border membrane vesicles we demonstrated that the channel-mediated calcium passive flux was saturable and was stimulated by a transmembrane electrical potential difference and inhibited by barium. We raised a monoclonal antibody (Mab 24A4) against the calcium channel, which allowed us to inhibit the channel-mediated calcium uptake. By immunocytochemistry, using Mab 24A4, we demonstrated that these channels are located at the apical membrane of hepatopancreatic B cells. Finally, by measuring the calcium uptake in R- and B-enriched cell suspensions, we showed that only the plasma membrane of the B cells expresses a channel-mediated calcium uptake inhibited by barium, verapamil and the monoclonal antibody 24A4. The plasma membrane of R cells did not show calcium channels.

Destruxins, cyclodepsipeptides, block the formation of actin rings and prominent clear zones and ruffled borders in osteoclasts

Bone-resorbing osteoclasts exhibit polarized morphological structures such as actin rings, clear zones, and ruffled borders. To gain insight into the mechanism of bone-resorbing activity of osteoclast and to discover new types of anti-resorptive agents, we have screened for natural compounds that inhibit the bone-resorbing activity of osteoclast-like multinucleated cells (OCLs). Destruxin B (DestB) and E (DestE), cyclodepsipeptides, were found to inhibit pit formation without affecting osteoclast differentiation and survival. Destruxins reversibly induced morphological changes in OCLs in a dose-dependent manner (DestB, 0.2-1 microM; DestE, 0.01-0.05 microM) and inhibited pit formation. Destruxin-induced morphological changes were accompanied by disruption of the actin rings in OCLs. The formation of actin rings in OCLs after adhesion was also inhibited by destruxins. Electron microscopical analysis revealed that destruxin-treated OCLs on dentine slices have no prominent clear zones and ruffled borders. The effective concentrations of destruxins on the morphological changes were almost the same as those that inhibited bone resorption in organ culture system. These results suggest that the anti-resorptive effects of destruxins result from induction of a disorder of the morphological structures in polarized OCLs.

Three different methods to evaluate microleakage of packable composites in Class II restorations

This in vitro study compared three different methods to evaluate detectable levels of microleakage in Class II restorations placed with five commercially available packable resin composites: Alert, Glacier, Pyramid, Solitaire 2 and SureFil. A flowable resin composite, Flow-It, was used to line all packable composites. The hybrid resin composite Z100 was also included. The adhesive system used with all groups was Scotchbond MultiPurpose Plus. Standard Class II cavities were prepared on the mesial (enamel margins) and distal (dentin margins) sides of the teeth with no communication between them. Based on a power analysis, 180 permanent human molars were randomly assign to each of six groups with 30 specimens per group. All restorative materials were placed following manufacturers' recommendations. Following restoration and thermocycling, the specimens were stored at room temperature in solutions of 45Ca, methylene blue and rhodamine B, sequentially. Microleakage was ordinal scored as 1 (no penetration), 2 (penetration up to one-third of the cervical floor), 3 (penetration beyond one-third of the cervical floor to the axial wall) and 4 (penetration along the axial wall) by two independent evaluators. Analysis of the occlusal surfaces was also accomplished following the same scheme. In this study, tracers/dyes were evaluated for differences in penetration using generalized estimating equation methodology applied to cumulative logistic regression models. The results showed that Rhodamine B detected more microleakage than 45Ca or methylene blue, and 45Ca generally detected more microleakage than methylene blue.

Effect of high concentration of glucose on dopamine release from pheochromocytoma-12 cells

To investigate the mechanism of the action of high concentration of glucose on transmitter release from neuronal cells, we examined the effect of high concentration of glucose on dopamine release from pheochromocytoma-12 (PC12) cells. When the cells were incubated with 9.0 or 13.5 mg/mL glucose (2- or 3-fold of the optimum glucose concentration for PC12 cells), dopamine release was increased in a dose-related manner. Glucose-induced increase in dopamine release was blunted by nicardipine, a Ca2+ channel blocker. Following addition of 13.5 mg/mL glucose, intracellular Ca2+ concentration was increased, which was eliminated by nicardipine. Administration of 9.0 or 13.5 mg/mL glucose induced membrane depolarization in a dose-related manner. Glucose-induced dopamine release was inhibited by pinacidil or diazoxide, adenosine triphosphate (ATP)-sensitive K+ channel (KATP channel) openers. These results suggest that a high concentration of glucose induced ATP production, which blocked the KATP channel to induce membrane depolarization, and increased intracellular Ca2+ concentration and dopamine release. When the cells were cultured with 9.0 or 13.5 mg/mL glucose for 7 days, high potassium chloride (KCl)-induced dopamine release and 45Ca2+ uptake were increased. These results suggest that long-term incubation with a high concentration of glucose increased the capacity of Ca2+ uptake to enhance depolarization-induced dopamine release from PC12 cells. These data taken together suggest that a high concentration of glucose induced activation of the Ca2+ channel to stimulate dopamine release from PC12 cells.

Ca2+ uptake and cellular integrity in rat EDL muscle exposed to electrostimulation, electroporation, or A23187

We tested the hypothesis that increased Ca2+ uptake in rat extensor digitorum longus (EDL) muscle elicits cell membrane damage as assessed from release of the intracellular enzyme lactate dehydrogenase (LDH). This was done by using 1) electrostimulation, 2) electroporation, and 3) the Ca2+ ionophore A23187. Stimulation at 1 Hz for 120-240 min caused an increase in 45Ca uptake that was closely correlated to LDH release. This LDH release increased markedly with temperature. After 120 min of stimulation at 1 Hz, resting 45Ca uptake was increased 5.6-fold compared with unstimulated muscles. This was associated with an eightfold increase in LDH release, and this effect was halved by lowering extracellular Ca2+ concentration ([Ca2+]o). The poststimulatory increase in resting 45Ca uptake persisted for at least 120 min. An acute increase in sarcolemma leakiness induced by electroporation markedly increased 45Ca uptake and LDH leakage. Both effects depended on [Ca2+]o. A23187 increased 45Ca uptake. Concomitantly, LDH leakage increased 18-fold within 30 min, and this effect was abolished by omitting Ca2+ from the buffer. We conclude that increased Ca2+ influx may be an important cause of cell membrane damage that arises during and after exercise or electrical shocks. Because membrane damage allows further influx of Ca2+, this results in positive feedback that may further increase membrane degeneration.

[Effect of nitrite-anions on Ca2+ transport into the sarcolemma of myometrium]

The influence of nitrite-anions physiological concentration on Ca2+ input into vesicles was investigated when using the "outside-out" vesicles of myometrial plasmalemma and 45Ca2+. It was established that nitrite-anions increased Ca(2+)-permeability of plasmalemma and increased the affinity of cation-transport system. The effects are probably connected with reversible modification of glutamate residues that bound and transported Ca2+ within the membrane. These findings showed that nitrite-anions are competitive activators of the passive calcium transport. On the other hand the decrease of Ca2+ affinity for the transport system under transmembrane proton scattering by the membrane, by rapid dissipation of transmembrane delta pH. It may be possible that the dissipation of transmembrane proton gradient changed the conformation of calcium transport system that calls the difference of kinetic mechanism of NO2- action in case of delta pH = 0 and delta pH = 1.5 on vesicle membranes.

Expression of calbindin-D28k (CaBP28k) in trophoblasts from human term placenta

Calbindin-D28k (CaBP28k) belongs to a large class of eucaryotic proteins that bind calcium (Ca2+) to a specific helix-loop-helix structure. To date, this protein was mainly linked to brain, kidneys, and pancreas. Here, we demonstrate for the first time the existence of CaBP8k in the human placental trophoblasts of the human term placenta. Placental Ca2+ transfer from maternal to fetus is crucial for fetal development, although the biochemical mechanisms responsible for this process are largely unknown. In the current study, we have investigated the 45Ca2+ uptake by human trophoblast cells in correlation with the expression CaBP28k. The expression of CaBP28k was determined by Northern blot analysis, reverse transcriptase polymerase chain reaction (RT-PCR), immunochemistry, and Western blot analysis. Indeed, Northern blot analysis revealed the presence of a CaBP28k transcript in syncytiotrophoblasts, cytotrophoblast cells, and HEK-293 cells. This was further confirmed by RT-PCR analysis followed by sequencing. In addition, anti-CaBP28k labeling was associated with cytotrophoblast and syncytiotrophoblast tissues in placental tissue sections and in vitro cultured cells. The presence of CaBP28k protein in these cells was confirmed by Western blotting. Cytotrophoblast cells isolated from human term placenta showed differentiation into syncytiotrophoblasts in culture according to the increase in hCG secretion. Both Ca2+ uptake and hCG secretion by trophoblasts increased gradually and were high at Day 4. Taken together, these data suggest that CaBP28k may play a role in Ca2+ transport or cell development in human trophoblast possibly trough Ca2+ buffering.

Regulation by glucocorticoids of cell differentiation and insulin-like growth factor binding protein production in cultured fetal rat nasal chondrocytes

Glucocorticoids (GCs) modulate insulin-like growth factor action in cartilage through mechanisms that are complex and insufficiently defined, especially in the context of cranio-facial growth. Because the family of IGF-binding proteins (IGFBP-1 to -6) is important in the regulation of IGF availability and bioactivity, we examined the effect of GCs on chondrocyte differentiation in correlation with IGFBP production in cultured fetal rat chondrocytes isolated from nasal septum cartilage of fetal rat. Dexamethasone (DEX) effects were tested before and at the onset of extracellular matrix maturation. DEX induced a dose-dependent increase in the size of cartilage nodule formed, (45)Ca incorporation into extracellular matrix, alkaline phosphatase activity, and sulfatation of glycosaminoglycans, maximal effects being obtained with a 10-mM DEX concentration. The IGFBPs produced by cultured chondrocytes were characterized in culture medium which had been conditioned for 24 h under serum-free conditions by these cells. Western ligand blotting with a mixture of [(125)I]IGF-I and -II revealed bands of 20, 24, 29, a 31-32 kDa doublet and a 39-41 kDa triplet which were differently regulated by DEX. Immunoblotting showed that following DEX exposure, IGFBP-3 and -6 were up-regulated whereas IGFBP-2, -5, and the 24 kDa band were down-regulated. The effect of DEX on both differentiation and IGFBP production showed a same dependence, and developed when extracellular matrix maturation had been just induced. The results obtained in this chondrocyte culture system show that production of IGFBPs is modulated by DEX at physiological concentrations thus regulating IGF availability and action, a control which could promote the primordial role of the rat nasal septum in craniofacial growth.

Increased [3H]phorbol ester binding in rat cerebellar granule cells and inhibition of 45Ca(2+) buffering in rat cerebellum by hydroxylated polychlorinated biphenyls

Our previous structure-activity relationship (SAR) studies indicated that the effects of polychlorinated biphenyls (PCBs) on neuronal Ca(2+) homeostasis and protein kinase C (PKC) translocation were associated with the extent of coplanarity. Chlorine substitutions at ortho position on the biphenyl, which increase the non-coplanarity, are characteristic of the most active congeners in vitro. In the present study, we investigated the effects of selected hydroxylated PCBs, which are major PCB metabolites identified in mammals, on the same measures where PCBs had differential effects based on structural configuration. These measures include PKC translocation as determined by [3H]phorbol ester ([3H]PDBu) binding in cerebellar granule cells, and Ca(2+) sequestration as determined by 45Ca(2+) uptake by microsomes isolated from adult rat cerebellum. All the selected hydroxy-PCBs with ortho-chlorine substitutions increased [3H]PDBu binding in a concentration-dependent manner and the order of potency as determined by E(50) (concentration that increases control activity by 50%) is 2',4',6'-trichloro-4-biphenylol (32 +/- 4 microM), 2',5'-dichloro-4-biphenylol (70 +/- 9 microM), 2,2',4',5,5'-pentachloro-4-biphenylol (80 +/- 7 microM) and 2,2',5'-trichloro-4-biphenylol (93 +/- 14 microM). All the selected hydroxy-PCBs inhibited microsomal 45Ca(2+) uptake to a different extent. Among the hydroxy-PCBs selected, 2',4',6'-trichloro-4-biphenylol is the most active in increasing [3H]PDBu binding as well as inhibiting microsomal 45Ca(2+) uptake. 3,5-Dichloro-4-biphenylol and 3,4',5-trichloro-4-biphenylol did not increase [3H]PDBu binding, but inhibited microsomal 45Ca(2+) uptake. This effect was not related to ionization of these two hydroxy-PCBs. Hydroxylated PCBs seemed to be as active as parent PCBs in vitro. These studies indicate that PCB metabolites such as hydroxy-PCBs might contribute significantly to the neurotoxic responses of PCBs.

Effects of corticosterone on Ca2+ uptake and myofibrillar disassembly in primary muscle cell culture

This study was done to examine the effects of corticosterone, a glucocorticoid, on Ca2+ uptake, proteolysis, and Ca2+ channels in primary cultures of chick muscle cells, to clarify the mechanism of glucocorticoid action on muscle proteolysis. Chick muscle cells were incubated for 24 h in a medium containing corticosterone (30 ng/ml) when the cells were confluent (6 days). To examine the contribution of Ca2+ channels, nifedipine, a Ca2+ channels antagonist, was used. Ca2+ uptake measured with 45CaCl2 was increased three-fold by corticosterone, with a peak at 12 h after the treatment started. The growth of the cells estimated from the protein content and creatine kinase activity was not affected by corticosterone. Proteolysis, evaluated with [3H]tyrosine as a label of the protein and Ntau-methylhistidine release, was unchanged by corticosterone. However, the amount of easily releasable myofilament as a measure of myofibrillar disassembly in the muscle cells was increased by corticosterone, and prevented by nifedipine. These results show that corticosterone increases Ca2+ uptake and starts myofibrillar protein breakdown.

Bone calcium turnover, formation, and resorption in bromocriptine- and prolactin-treated lactating rats

To evaluate the effect of endogenous prolactin (PRL) on bone metabolism, we studied bone calcium turnover by the (45)Ca kinetic method and bone formation and resorption by bone histomorphometry and biochemical markers in 13-wk-old lactating Wistar rats. For 1 wk, the animals received daily administration of 0.9% NaCl (control) intraperitoneally, 6 mg of bromocriptine/ kg of body wt intraperitoneally, or 6 mg of bromocriptine/kg of body wt plus 2.5 mg of ovine PRL/kg of body wt subcutaneously. Bromocriptine, a dopaminergic inhibitor of endogenous PRL secretion, significantly decreased calcium ion deposit rate and calcium resorption rate in femur, tibia, vertebrae 5 and 6, and sternum by 20- 42%. By contrast, calcium resorption rate of the vertebrae and the sternum of the PRL-treated group was higher than that of controls, whereas the tibia and sternum exhibited a greater net loss of calcium. The suppression of bone calcium turnover in the bromocriptine-treated group was further supported by a significant decrease in the urinary deoxypyridinoline, a biochemical index of bone resorption, and the histomorphometric data, which showed changes indicative of suppressed bone resorption and formation. The histomorphometric data from the PRL-treated group were not different from those of the control group with the exception of an increase in the longitudinal growth rate. The results suggested a role of endogenous PRL in the stimulation of bone turnover during lactation.

In depolarized and glucose-deprived neurons, Na+ influx reverses plasmalemmal K+-dependent and K+-independent Na+/Ca2+ exchangers and contributes to NMDA excitotoxicity

Cerebellar granule cells (CGCs) express K+-dependent (NCKX) and K+-independent (NCX) plasmalemmal Na+/Ca2+ exchangers which, under plasma membrane-depolarizing conditions and high cytosolic [Na+], may reverse and mediate potentially toxic Ca2+ influx. To examine this possibility, we inhibited NCX or NCKX with KB-R7943 or K+-free medium, respectively, and studied how gramicidin affects cytosolic [Ca2+] and 45Ca2+ accumulation. Gramicidin forms pores permeable to alkali cations but not Ca2+. Therefore, gramicidin-induced Ca2+ influx is indirect; it results from fluxes of monovalent cations. In the presence of Na+, but not Li+ or Cs+, gramicidin induced Ca2+ influx that was inhibited by simultaneous application of KB-R7943 and K+-free medium. The data indicate that gramicidin-induced Na+ influx reverses NCX and NCKX. To test the role of NCX and/or NCKX in excitotoxicity, we studied how NMDA affects the viability of glucose-deprived and depolarized CGCs. To assure depolarization of the plasma membrane, we inhibited Na+,K+-ATPase with ouabain. Although inhibition of NCX or NCKX reversal failed to significantly limit 45Ca2+ accumulation and excitotoxicity, simultaneously inhibiting NCX and NCKX reversal was neuroprotective and significantly decreased NMDA-induced 45Ca2+ accumulation. Our data suggest that NMDA-induced Na+ influx reverses NCX and NCKX and leads to the death of depolarized and glucose-deprived neurons.