Evidence that intracellular Ca2+ mediates the effect of α-ketoisocaproic acid on the phosphorylating system of cytoskeletal proteins from cerebral cortex of immature rats

In this study we investigated the involvement of Ca2+ on the effects of alpha-ketoisocaproic acid (KIC), the main metabolite accumulating in maple syrup urine disease (MSUD), on the phosphorylating system associated with the intermediate filament (IF) proteins in slices from cerebral cortex of 9-day-old rats. We first observed that KIC significantly decreased the in vitro phosphorylation of IF proteins in brain slices. KIC-induced dephosphorylation was mediated especially by the protein phosphatase PP2B, a Ca2+-dependent protein phosphatase, but also by PP2A. We also demonstrated the involvement of Ca2+-dependent mechanisms in the KIC effects using the specific L-voltage-dependent Ca2+ channels (L-VDCC) inhibitor nifedipine, the NMDA antagonist DL-AP5 and the intracellular Ca2+ chelator BAPTA-AM. Blockage of Ca2+ channels or chelating intracellular Ca2+ completely prevented the effects of KIC on the phosphorylating system associated to IF proteins. In addition, we verified that KIC increased 45Ca2+ uptake in brain slices after 3 and 30 min incubation. Taken together, our present data indicate that KIC increase intracellular Ca2+ levels, probably promoting the activation of calcineurin. These results might be associated with the increased dephosphorylation of the IF proteins in slices of cerebral cortex of immature rats exposed to KIC at similar concentrations from those found in blood and tissues of patients with MSUD.

Influence of a Chinese crude drug on Ca2+ influx and efflux in rat visceral organs: investigation and evaluation by 45Ca

The influences of a Chinese crude drug, Herba Epimedii, (HE), on Ca2+ influx and efflux in the isolated rat aorta and some visceral organs were evaluated by using 45Ca as a radioactive tracer. Additionally, its protective effect on myocardial ischemia was investigated in live animals. The results indicated that HE has significant influence on Ca2+ influx and efflux in the isolated rat aorta, heart, and kidney, in that it can markedly block 45Ca entering into cell and can facilitate efflux of intracellular Ca2+. However, among the three kinds of extracts from HE, the alkali extracts have the most obvious effect on calcium channels in visceral organs. Even if the alkali extracts are diluted by water for 10 times, the material still has a rather strong inhibition effect on calcium channels. Fortunately, the three kinds of extracts have favorable protective effect on myocardial ischemia induced by drugs or by the ligation of the coronary artery. This is consistent with the results about the Ca2+ influx and efflux obtained by isotope tracer technique, and implies that the Chinese crude drug has attractive potential for the treatment of heart, cerebrovascular and other diseases.

41Ca and accelerator mass spectrometry to monitor calcium metabolism in end stage renal disease patients

BACKGROUND

Monitoring bone resorption with measurements of bone density and biochemical markers is indirect. We hypothesized that bone resorption can be studied directly by serial measurements of the ratio (41)Ca/Ca in serum after in vivo labeling of calcium pools with (41)Ca. We report the preparation of an intravenous (41)Ca dose suitable for humans, an analytical method for determining (41)Ca/Ca isotope ratios in biological samples, and studies in human volunteers.

METHODS

(41)Ca was formulated and aliquoted into individual vials, and to the extent possible, the (41)Ca doses were tested according to US Pharmacopeia (USP) guidelines. A 10 nCi dose of (41)Ca was administered intravenously to 4 end stage renal disease (ESRD) patients on hemodialysis and 4 healthy control individuals. Distribution kinetics were determined over 168 days. Calcium was isolated with 3 precipitation steps and a cation-exchange column, and (41)Ca/Ca ratios in serum were then measured by accelerator mass spectrometry.

RESULTS

The dosing solution was chemically and radiologically pure, contained <0.1 endotoxin unit/mL, and passed USP sterility tests. Quantification of (41)Ca/Ca ratios was linear from 6 x 10(-14) to 9.1 x 10(-10). The run-to-run imprecision (as CV) of the method was 4% at 4.6 x 10(-11) and 6% at 9.1 x 10(-10). The area under the curve of (41)Ca in the central compartment vs time was significantly less for ESRD patients than for controls (P < 0.005).

CONCLUSIONS

Isotope ratios spanning 5 orders of magnitude can be measured by accelerator mass spectrometry with excellent precision in the range observed in samples collected from patients who have received 10 nCi of (41)Ca. The (41)Ca at this dose caused no adverse effects in 8 volunteers. This is the first report of the use of (41)Ca to monitor differences in bone turnover between healthy individuals and ESRD patients.

Methodological considerations in measuring human calcium absorption: relevance to study the effects of inulin-type fructans

During the last 50 years, a variety of methods have been developed to estimate Ca absorption in man. Mass balances were initially used, but these were unable to accurately measure fractional Ca absorption because they cannot distinguish unabsorbed dietary Ca from endogenous faecal Ca excretion (excretion of previously absorbed Ca back into the gut). A number of isotopic methods have been developed that can measure true fractional Ca absorption, employing radioisotopes, stable isotopes, or both. Different methods involve collection of urine, faecal or plasma samples. Of the currently available methods, the dual isotope tracer method with a timed urine collection is probably the most precise and reliable. It is also relatively straightforward to carry out and avoids the need for a faecal collection. The purpose of the present paper is to discuss the general advantages and disadvantages of the different methods of Ca absorption. In addition, the limitations the different methods have in examining the possible effects of non-digestible oligosaccharides on Ca absorption will be discussed.

Calcium antagonistic effects of Chinese crude drugs: Preliminary investigation and evaluation by 45Ca

Coronary and other diseases in cardiac or brain blood vessels are considered to be due to the excessive influx of Ca(2+) into cytoplasm. If Ca(2+) channels in cell membrane are blocked by medicines or other substances with considerable calcium antagonistic effects, these diseases might be cured or controlled. The influence of some Chinese crude drugs, including Crocus sativus, Carthamus tinctorius, Ginkgo biloba and Bulbus allii macrostemi on Ca(2+) influx in isolated rat aortas was investigated by using (45)Ca as a radioactive tracer, and their calcium antagonistic effects were evaluated. It can be noted that Ca(2+) uptake in isolated rat aorta rings in normal physiological status was not markedly altered by these drugs, whereas the Ca(2+) influxes induced by norepinephrine of 1.2 micromol/L and KCl of 100 mmol/L were significantly inhibited by Crocus, Carthamus and Bulbus in a concentration-dependent manner, but not by Ginkgo. The results show that extracellular Ca(2+) influx through receptor-operated Ca(2+)channels and potential-dependent Ca(2+)channels can be blocked by Crocus, Carthamus and Bulbus. This implies that these Chinese crude drugs have obvious calcium antagonistic effects.

Effects of acute amphetamine administration on AMPA-mediated synaptic activity and expression of AMPA receptor subunit 2 of brain neurons

We investigated the role of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptor (AMPAR) in mechanisms underlying the action of amphetamine (Amph) on brain neurons, for AMPAR has been proposed to participate in psychotic and neurodegenerative disorders. In the cultured rat brain cortical neurons pretreated with 1 microM Amph for 1 h, the accumulation of 45Ca2+ driven by 10 min incubation with 100 microM AMPA was reduced by about 36%. This Amph-induced decrease seems to involve L-type voltage-gated Ca2+ channels, because the AMPA-induced 45Ca2+ uptake was blocked by 70% and 80%, respectively, for untreated and Amph-treated neurons in the presence of nifedipine (1 microM), an antagonist to L-type calcium channels. Whole-cell, patch-clamp recording revealed that AMPA-elicited current amplitude became 26% lower than the control in Amph-treated cultured neurons. Moreover, Amph treatment down-regulated the level of flip-form glutamate receptor 2 (GluR2) mRNA by 27% in cultured neurons but did not change the expression of GluR2 proteins and flop-form mRNA, as detected by quantitative immunocytochemistry and in situ hybridization. In contrast, in postnatal day 4 rats at 1 h after receiving one intraperitoneal injection of 5 mg/kg of Amph, levels of flip GluR2 mRNA were up-regulated by 13% and 18% in neurons of motor cortex layer 5 and pyramidal neurons of hippocampal CA3, respectively. The data suggest that acute action of Amph on brain neurons is possibly associated with decreased AMPA-mediated Ca2+ influx and current amplitude, as well as modified expression of the GluR2 mRNA.

Ca release induced by cyclic adenosine diphosphoribose (cADPr) in sea urchin egg homogenates: mechanisms of release and heterogeneity of the Ca compartments

A rapid superfusion system measuring the amounts, kinetics, and Ca dependencies of released 45Ca, was used to examine the effects of ryanodine (RY), caffeine (CF), and cyclic ADP ribose (cADPr) on sea urchin egg homogenates. The RY-sensitive compartment had more than twice the Ca release capacity of the CF-sensitive or cADPr-sensitive compartment. cADPr-stimulated 45Ca release required calcium with half-maximal activation at approximately 0.2 to 0.6 microM [Ca2+]. K(1/2) for cADPr activation was approximately 100 nM, and in spite of the Ca requirement for cADPr-stimulated release, the cADPr affinity was not affected by [Ca2+]. Peak 45Ca release rate with cADPr (3 microM) was greater than with CF (20 mM), yet the release amounts were similar and both were [Ca2+]-dependent. When activated with CF and cADPr simultaneously, 45Ca release was large and, no longer [Ca2+]-dependent. Mg competitively inhibited the Ca activation site(s), yet did not inhibit the activation with CF-plus-cADPr. Pre-release of 45Ca by cADPr with low (approximately 0.1 microM) [Ca2+] right-shifted the [Ca2+] dependence of the remaining cADPr-response. These data suggest that (a) only a portion of RY-sensitive compartments empty when stimulated with cADPr or CF, (b) Ca and cADPr act on non-interacting sites, and (c) cADPr-sensitive compartments represent a heterogeneous population with different [Ca2+] dependencies.

Phosphorimaging detection and quantitation for isotopic ion flux assays

A 96-well-microplate-based ion flux method utilizing readily available autoradiographic phosphorimaging detection is described. Nicotinic acetylcholine receptor-mediated (22)Na influx in four cultured cell lines provided satisfactory concentration-response data for epibatidine and several other nicotinic agonists. The data were consistent with data obtained using standard 6-well assays. Assays for nicotinic-receptor-mediated (86)Rb efflux produced data similar to data obtained with the (22)Na influx assay. However, assays for (45)Ca influx were not successful, although (45)Ca was readily detected and quantified. Voltage-gated sodium channel-mediated (22)Na influx in a neuroblastoma cell line allowed assay of the effects of such sodium channel activators as batrachotoxin and a pumiliotoxin B/scorpion venom combination. Phosphorimaging detection allows for reliable beta counting of up to 1,200 simultaneous samples with excellent sensitivity and is amenable for application to high-throughput screening.

Dopamine D2 Receptor Availability is Associated with Subjective Responses to Alcohol

BACKGROUND

The mesolimbic dopaminergic system is thought to mediate alcohol abuse and dependence. Determining the relationship between in vivo dopamine and the subjective response to alcohol could improve understanding of the mechanisms that lead to alcohol abuse and dependence. Here, we examined the relationship between dopamine D2 receptors in the nucleus accumbens and scores of perceived "high" and "intoxication" during an intravenous (IV) alcohol infusion.

METHODS

Nine healthy control subjects received [C]raclopride PET scanning at baseline. Eight subjects received a second [C]raclopride scan during a pharmacodynamically modeled and controlled rise of IV alcohol, followed by steady state (60 mg% +/- 5 mg%) alcohol infusion. Numerical ratings of "high" and "intoxication" were tested for correlations with measures of dopaminergic function.

RESULTS

Baseline D2 receptor availability in the left nucleus accumbens was significantly correlated with peak perceived "intoxication" (p = 0.02) and marginally correlated with peak perceived "high" (p = 0.07).

CONCLUSIONS

Resting D2 receptor availability may predict healthy subject responses to alcohol exposure.

Alteration of contractile function and calcium ion movements in vascular smooth muscle by gentamicin and other aminoglycoside antibiotics

Experiments were conducted to examine the effects of certain aminoglycoside antibiotics on contractile responses and related calcium ion (Ca(2+)) movements in isolated vascular smooth muscle. Gentamicin, kanamycin, and streptomycin decreased contractile responses produced by norepinephrine, histamine, and high K(+) in rabbit aortic strips. The inhibitory action of these antibiotics on mechanical function was more pronounced when the Ca(2+) concentration of the bathing solution was decreased from 1.5 mM (normal Ca(2+) solution) to 0.05 mM (low Ca(2+) solution). The uptake of radiocalcium ((45)Ca) into the isolated media-intimal layer of rabbit aortae was decreased in a maintained manner by each antibiotic. With gentamicin, the inhibitory effect on (45)Ca uptake was shown to be dependent upon the concentration of gentamicin employed and to be more evident in a 0.1 mM Ca(2+) solution than in a normal Ca(2+) solution. In addition, the rate of (45)Ca efflux from the rabbit aortic media-intimal layer was increased in a sustained manner by gentamicin, streptomycin, and kanamycin. Furthermore, contractile responses induced by high K(+) and norepinephrine in canine carotid arterial strips were inhibited by gentamicin. Present findings indicate that aminoglycoside antibiotics interfere with Ca(2+)-linked events leading to activation of the contractile mechanism of vascular smooth muscle. These in vitro findings may partially explain the occurrence of in vivo cardiovascular depression that has occasionally been observed after the administration of chemically related antimicrobial agents.

Impairment of smooth muscle function of rat thoracic aorta in an endothelium-independent manner by long-term administration of N(G)-nitro-L-arginine methyl ester

In this study, we aimed to elucidate whether the daily hypertensive dose of long-term N(G)-nitro-l-arginine methyl ester (l-NAME) treatment, could make a difference between endothelial and smooth muscle functions in rat thoracic aorta. We test the hypothesis that high-dose, long-term l-NAME treatment has a depressive effect on vascular smooth muscle contractile activity which is not related with nitric oxide (NO) synthesis inhibition. After 14 days of treatment, isometric tension and (45)Ca(2+) influx were measured in aortic tissues isolated from l-NAME(10) and l-NAME(100) hypertensive (10 and 100 mg/kg/day, systolic blood pressures 167 +/- 7 and 172 +/- 10 mmHg, respectively) and control normotensive rats (132 +/- 7 mmHg). In l-NAME(10)- and l-NAME(100)-treated rats, acetylcholine-induced relaxation in aortic rings was suppressed with no significant difference between the treatments. l-NAME(100) (but not l-NAME(10)) treatment, significantly inhibited contractile responses to phenylephrine, angiotensin II, and K(+) (80 mm) in endothelium-intact tissues. The effect of l-NAME(100) on phenylephrine-induced contractile responses was not observed after 3 days of treatment. In endothelium-denuded aortic tissues of l-NAME(100) (but not l-NAME(10))-treated rats, phenylephrine (1 x 10(-6) m)- and K(+) (80 mm)-induced contractions and (45)Ca(2+) influxes were significantly reduced. In Ca(2+)-free medium (0.1 mm EDTA), on the contrary, the transient contractions obtained by either phenylephrine (1 x 10(-6) m) or caffeine (1 x 10(-2) m), or the sustained contractions induced by 12-o-tetradecanoylphorbol-13-acetate (1 x 10(-6) m; a protein kinase C activator) in endothelium-denuded aortic rings, were not modified by both l-NAME treatments. These results indicate that in aortic rings from l-NAME hypertensive rats, low and high doses, long-term l-NAME administration may be associated with equivalent inhibition in NO-dependent vasodilator tone (corresponding to equivalent hypertension values); whereas only high-dose, long-term l-NAME administration produces an endothelium-independent decrease in vasocontrictor activity, at least partly explained by a reduction in extracellular Ca(2+) influx.

Differential Effects of Commercial Polybrominated Diphenyl Ether and Polychlorinated Biphenyl Mixtures on Intracellular Signaling in Rat Brain in Vitro

Polybrominated diphenyl ethers (PBDEs) are widely used as flame retardants and have been detected in human blood, adipose tissue, and breast milk. Developmental and long-term exposures to these contaminants may pose a human health risk, especially to children. Previously, we demonstrated that polychlorinated biphenyls (PCBs), which are neurotoxic and structurally similar to PBDEs, perturbed intracellular signaling events, including calcium homeostasis and subsequent events such as protein kinase C (PKC), which are critical for the normal function and development of the nervous system. The objective of the present study was to test whether commercial PBDE mixtures (DE-71, a pentabrominated dipheyl ether mixture, and DE-79, a mostly octabromodiphenyl ether mixture) affected intracellular signaling mechanisms in a similar way to that of PCBs and other organohalogens, as an attempt to understand the common mode of action for these persistent chemicals. PKC translocation was studied by determining (3)H-phorbol ester ((3)H-PDBu) binding in rat cerebellar granule cells, and calcium buffering was determined by measuring (45)Ca(2+) uptake by microsomes and mitochondria isolated from adult male rat brain (frontal cortex, cerebellum, and hippocampus). As seen with PCBs, DE-71 increased PKC translocation and inhibited (45)Ca(2+) uptake by both microsomes and mitochondria in a concentration-dependent manner. The effect of DE-71 on (45)Ca(2+) uptake seems to be similar in all three brain regions. Between the two organelles, DE-71 inhibited mitochondrial (45)Ca(2+) uptake to a greater extent than microsomal (45)Ca(2+) uptake. DE-79 had no effects on either neurochemical event even at 30 mug/ml. Aroclor 1254 altered both events to a greater extent compared to DE-71 on a weight basis. When the results were compared on a molar basis, Aroclor 1254 altered PKC translocation and microsomal (45)CaP(2+) uptake to a greater extent than DE-71, however, Aroclor 1254 and DE-71 equally affected mitochondrial (45)Ca(2+) uptake. These results indicate that PBDEs perturbed intracellular signaling mechanisms in rat brain as do other organohalogen compounds and the efficacy between the commercial PCB and PBDE mixtures seem to vary with different endpoints.

Mode of action of taurine as a neuroprotector

Previously, it has been shown that taurine exerts its protective function against glutamate-induced neuronal excitotoxicity through its action in reducing glutamate-induced elevation of intracellular free calcium, [Ca2+]i. Here, we report the mechanism underlying the effect of taurine in reducing [Ca2+]i. We found that taurine inhibited glutamate-induced calcium influx through L-, P/Q-, N-type voltage-gated calcium channels (VGCCs) and NMDA receptor calcium channel. Surprisingly, taurine had no effect on calcium influx through NMDA receptor calcium channel when cultured neurons were treated with NMDA in Mg2+-free medium. Since taurine was found to prevent glutamate-induced membrane depolarization, we propose that taurine protects neurons against glutamate excitotoxicity by preventing glutamate-induced membrane depolarization, probably through its effect in opening of chloride channels and, therefore, preventing the glutamate-induced increase in calcium influx and other downstream events.

Disruption of Neuronal Calcium Homeostasis after Chronic Aluminium Toxicity in Rats

The present study was designed to investigate the possible effects of chronic aluminium exposure on the various aspects of calcium homeostasis in rat brain. Chronic aluminium administration caused significant rise in the intrasynaptosomal calcium levels. The activity of major calcium-expelling enzyme, i.e. Ca2+ ATPase was found to be lowered. Also, the calcium uptake via voltage-operated calcium channels increased significantly. Similar to the increase in intrasynaptosomal calcium, calpain activity was found to be increased. The results presented here, indicate that the toxic effects of aluminium could be mediated through modifications in the intracellular calcium homeostasis, which may lead to impaired neuronal function.

Effects of PCB 84 enantiomers on [3H]-phorbol ester binding in rat cerebellar granule cells and 45Ca2+-uptake in rat cerebellum

There is evidence that polychlorinated biphenyl (PCB) congeners with ortho chlorine substituents have potential to cause neurotoxicity. Many PCB congeners implicated in these neurotoxic effects are chiral. It is currently unknown if the enantiomers of chiral PCB congeners have different neurotoxic effects. We herein report the effect of racemic 2,2',3,3',6-pentachlorobiphenyl (PCB 84) and its enantiomers on two neurochemical measures, protein kinase C (PKC) translocation as determined by [3H]-phorobol ester binding in cerebellar granule cells and Ca2+-sequestration as determined by 45Ca2+-uptake by microsomes isolated from adult rat cerebellum. Both (+)- and (-)-PCB 84 increased [3H]-phorobol ester binding in a concentration-dependent manner with (-)-PCB 84 being slightly more potent. Racemic PCB 84 was significantly more potent and efficacious than the pure enantiomers alone. (-)- and (+)-PCB 84 each inhibited microsomal 45Ca2+-uptake to a similar extent, whereas racemic PCB 84 was more potent and efficacious. These results indicate that PCB 84 enantiomers alone can have different potencies, and these may differ from that of the racemic mixture, observations that may have important implications for understanding the mechanisms of neurotoxicity of chiral PCB congeners.

Injury-induced alterations in N-methyl-D-aspartate receptor subunit composition contribute to prolonged 45calcium accumulation following lateral fluid percussion

Cells that survive traumatic brain injury are exposed to changes in their neurochemical environment. One of these changes is a prolonged (48 h) uptake of calcium which, by itself, is not lethal. The N-methyl-D-aspartate receptor (NMDAR) is responsible for the acute membrane flux of calcium following trauma; however, it is unclear if it is involved in a flux lasting 2 days. We proposed that traumatic brain injury induced a molecular change in the NMDAR by modifying the concentrations of its corresponding subunits (NR1 and NR2). Changing these subunits could result in a receptor being more sensitive to glutamate and prolong its opening, thereby exposing cells to a sustained flux of calcium. To test this hypothesis, adult rats were subjected to a lateral fluid percussion brain injury and the NR1, NR2A and NR2B subunits measured within different regions. Although little change was seen in NR1, both NR2 subunits decreased nearly 50% compared with controls, particularly within the ipsilateral cerebral cortex. This decrease was sustained for 4 days with levels returning to control values by 2 weeks. However, this decrease was not the same for both subunits, resulting in a decrease (over 30%) in the NR2A:NR2B ratio indicating that the NMDAR had temporarily become more sensitive to glutamate and would remain open longer once activated. Combining these regional and temporal findings with 45calcium autoradiographic studies revealed that the degree of change in the subunit ratio corresponded to the extent of calcium accumulation. Finally, utilizing a combination of NMDAR and NR2B-specific antagonists it was determined that as much at 85% of the long term NMDAR-mediated calcium flux occurs through receptors whose subunits favor the NR2B subunit. These data indicate that TBI induces molecular changes within the NMDAR, contributing to the cells' post-injury vulnerability to glutamatergic stimulation.

Does the response of bone mass to calcium supplements depend on calcium absorption efficiency?

OBJECTIVE

Calcium supplements can reduce bone resorption and slow bone loss after the menopause, but these effects may be limited by poor intestinal absorption. Since the increase in blood ionised calcium and decrease in serum parathyroid hormone after a calcium load are diminished in patients with poor calcium absorption, we aimed to see whether the response of bone mineral content (BMC) to calcium is related to initial calcium absorption.

DESIGN

We retrospectively examined the changes in forearm BMC in 164 patients (139 women and 25 men) receiving calcium therapy alone for low bone density in a university hospital.

METHODS

BMC was measured in a Molsgaard single energy absorptiometer and calcium absorption in a single blood sample 1 h after a dose of 5 microCi (45)Ca in 20 mg calcium carrier. Results were analysed by simple and multiple regression analysis.

RESULTS

Mean forearm BMC did not change significantly over the mean 43 (S.D., 33) months of treatment (1.023 (0.247) to 1.017 (0.246) g/cm). The annual percentage of change was positively related to both body weight (r=0.180; P=0.020) and radiocalcium absorption (r=0.185; P=0.017). Multiple linear regression confirmed that both variables contributed to the change in BMC (P=0.023 and 0.019 respectively). The mean annual percentage of change in BMC on calcium therapy was not related to age, initial BMC, serum 1,25-dihydroxyvitamin D or fasting urinary calcium/creatinine ratio.

CONCLUSIONS

These results support our earlier studies which suggest that poor calcium absorption limits the response of bone to calcium supplements.

Association of Paracellin-1 with ZO-1 Augments the Reabsorption of Divalent Cations in Renal Epithelial Cells

Paracellin-1 (PCLN-1) belongs to the claudin family of tight junction proteins and possibly plays a critical role in the reabsorption of magnesium and calcium. So far, the physiological properties of PCLN-1 have not been clarified. In the present study, we investigated whether PCLN-1 is associated with ZO-1. We also investigated whether (45)Ca(2+) transport across the paracellular barrier is affected by this association. In vitro binding analysis using glutathione S-transferase fusion protein showed that the C-terminal TRV sequence, especially Thr and Val residues, of PCLN-1 interacts with ZO-1. Next, PCLN-1 was stably expressed in Madin-Darby canine kidney cells using a FLAG tagging vector. ZO-1 was co-immunoprecipitated with the wild-type PCLN-1 and the alanine substitution (TAV) mutant. However, mutants of the deletion (Delta TRV) and the alanine substitution (ARV and TRA) inhibited the association of PCLN-1 with ZO-1. Confocal immunofluorescence demonstrated that the wild-type PCLN-1 and the TAV mutant localized in the tight junction along with ZO-1, but the Delta TRV, ARV, and TRA mutants were widely distributed in the lateral membrane including the tight junction area. Interestingly, monolayers of cells expressing the wild-type PCLN-1 and the TAV mutant showed higher activities of (45)Ca(2+) transport from apical to basal compartments, compared with those expressing the Delta TRV, ARV, and TRA mutants and the mock cells. (45)Ca(2+) transport was inhibited by increased magnesium concentration suggesting that magnesium and calcium were competitively transported by PCLN-1. It was noted that a positive electrical potential gradient enhanced (45)Ca(2+) transport from apical to basal compartments without affecting the opposite direction of transport. Thus, PCLN-1 localizes to the tight junction followed by association with ZO-1, and the PCLN-1.ZO-1 complex may play an essential role in the reabsorption of divalent cations in renal epithelial cells.

Basal calcium entry in vascular smooth muscle

Basal calcium leak into smooth muscle was identified 30 years ago yet remains poorly understood. We characterized this leak measuring 45Ca2+ uptake into cultured rat aortic smooth muscle cells. Wash solution (0 degrees C) containing lanthanum (3 mM) removed extracellular tracer and increased cellular 45Ca2+ retention more effectively than EGTA (0.2 mM). Basal Ca2+ entry was 1.45 x 10(9) Ca2+ x cell(-1) x min(-1). This translated to approximately 250 micromol(-1) x min(-1) given cell volumes of 4-15 pl as determined by 3-D image reconstruction. Gadolinium (100 microM) blocked 80% of the leak and exhibited a biphasic concentration-response relation (IC50s=1 microM and 2 mM). Organic ion channel blockers also inhibited approximately 80% of the leak; 45% by nifedipine (10 microM), 7% was exclusively blocked by SKF 96365 (1-[b-[3-(4-Methoxyphenyl)propoxy]-4-methoxyphenethyl]-1H-imidazole) (50 microM) and 23% was exclusively sensitive to 2-aminoethoxy-diphenylborate (2-APB, 75 microM). Reverse transcriptase polymerase chain reaction revealed TrpC1, 4 and 6 mRNA, and we propose that 2-APB may selectively block TrpC4-containing channels. We conclude that basal Ca2+ entry is mainly due to a basal open probability of excitable Ca2+ -channels.

Bone resorption activity of osteolytic metastatic lung and breast cancers

Production of bone resorption mediators and bone resorption activity were compared among osteolytic metastatic cancers, normal bone tissues, and soft tissue metastatic cancers to search for the possible factors leading to cancer-induced bone resorption. Twenty-five patients with untreated osteolytic metastatic breast or non-small cell lung cancers consisted of the study group. Normal bone tissues obtained from the same patient were used as internal controls; and tumor tissues from patients with soft tissue metastasis were used as external controls. Serum and urinary bone turnover markers were measured. Tissues harvested during surgery were subjected to tissue culture. The levels of prostaglandin E2 (PGE2), tumor necrosis factor-alpha (TNF-alpha), and interleukin-6 (IL-6) in the supernatant after 72 h of culture were measured. Bone resorption activity was measured by calcium release from cultured calvarias, and bone volume as well as osteoclast number in bone sections. Patients with osteolytic metastatic cancers showed significantly decreased serum osteocalcin, increased serum alkaline phosphatase, and urinary deoxypyridinoline levels. Osteolytic metastatic cancers produced significantly more PGE2 than both controls. Conditioned medium from osteolytic metastatic tumors showed significantly enhanced bone resorption activity, and indomethacin significantly reduced this activity. Levels of PGE2, and bone resorption activity increased in osteolytic tumor tissues than soft tissue metastatic tissues in the same patient indicated that the same tumor cells might respond differently to different microenvironments. Our observation showed that PGE2 was produced by osteolytic metastatic cancers and stimulated bone resorption in mice calvarias. PGE2 inhibitor may be applicable in reducing bone resorption by osteolytic metastatic cancers.

Sensitization of vanilloid receptor 1 induced by bradykinin via the activation of second messenger signaling cascades in rat primary afferent neurons

Vanilloid receptor 1 was recently reported to play an important role in hyperalgesia, but the mechanisms by which this receptor is activated by endogenous inflammatory mediators, such as bradykinin and nerve growth factor, are not yet fully understood. Here, we investigated whether bradykinin, which is a pain-producing inflammatory mediator, sensitizes vanilloid receptor 1 by inducing the activation of cyclooxygenases, phospholipase C and phospholipase A2 in rat dorsal root ganglion cells. We demonstrated this using 45Ca2+ uptake and inositol phosphates accumulation assays, bradykinin activates phospholipase C and cyclooxygenase-1 through the bradykinin B2 receptor. The bradykinin B2 receptor then sensitizes vanilloid receptor 1 activity by facilitating non-selective Ca2+ channel activity, increasing the intracellular Ca2+ concentration from the extracellular pool. These methods would be useful for screening new drugs for activity at vanilloid receptor 1. These data suggest that endogenous substances produced by several enzymes may be capable of producing a synergistic response involving the vanilloid receptor 1.

Release of calcium from intracellular stores and subsequent uptake by mitochondria are essential for the candidacidal activity of an N-terminal peptide of human lactoferrin

OBJECTIVES

Earlier studies showed that mitochondrial damage is a hallmark of the candidacidal activity of an N-terminal peptide of human lactoferrin, further referred to as hLF(1-11). Since uptake of Ca(2+) by mitochondria may be essential for their activation, the aim of this study was to define the role of Ca(2+) in killing of Candida albicans by the hLF(1-11) peptide.

METHODS

The effect of compounds interfering with Ca(2+) homeostasis on the hLF(1-11)-induced candidacidal activity, changes in mitochondrial membrane potential, and reactive oxygen species production were evaluated using a killing assay, rhodamine 123 staining, and 2',7'-dichlorofluorescein diacetate, respectively. The increase in cellular Ca(2+) content was measured using (45)Ca(2+).

RESULTS

Our results revealed that Ruthenium Red, which inhibits the mitochondrial Ca(2+)-uniporter and the voltage-sensitive Ca(2+) release from internal stores, blocked (P<0.05) the hLF(1-11)-induced candidacidal activity as well as changes in the membrane potential of mitochondria, and reactive oxygen species production. Oxalate, which precipitates Ca(2+) in intracellular organelles, decreased (P<0.05) the peptide-induced changes in the membrane potential of mitochondria, reactive oxygen species production, and candidacidal activity. Furthermore, the Ca(2+) ionophore ionomycin combined with high CaCl(2) concentrations enhanced the hLF(1-11)-induced candidacidal activity. Moreover, hLF(1-11) caused an influx of Ca(2+) from the extracellular medium into C. albicans reaching a three-fold increase at 2 h, whereas no increase was found in unexposed cells. In agreement, the Ca(2+)-chelator EGTA blocked the peptide-induced candidacidal activity.

CONCLUSIONS

Ca(2+) release from intracellular stores, probably through subsequent mitochondrial Ca(2+) uptake, is essential for the hLF(1-11)-induced candidacidal activity.

The role of sodium ions in the pathogenesis of skeletal muscle damage in broiler chickens

The effect of sodium ions (Na+) on calcium (Ca2+)-mediated muscle damage in broiler chickens was investigated using an in vitro muscle preparation. Muscle Ca2+ accumulation was determined by 45Ca2+ uptake. Muscle damage was assessed by measurement of the efflux of the intracellular enzyme creatine kinase (CK) into the incubation medium. Loading muscle cells with Na+ by means of the sodium ionophore monensin led to concentration-dependent (25 to 200 microM) increases in 45Ca2+ uptakes and corresponding and proportional CK losses. The greatest responses occurred at 100 microM ionophore or greater, reflected in a 49% increase (P < 0.05) in 45Ca2+ uptake and an associated 140%-fold increase (P < 0.001) in CK efflux. Inhibition of muscle Na+/K+-ATPase activity with ouabain (2 mM) induced a 56% increase in 45Ca2+ uptake and a 60%-fold increase (P < 0.001) in total CK loss. The combined use of ionophore and ouabain resulted in 90 and 130%-fold elevations in 45Ca2+ uptake and CK loss, respectively. In monensin-treated muscles, inhibition of external Ca2+ influx from the incubation medium by chelation with 1,2 bis(2-aminophenoxy)ethane-N,N,N',N' tetracetic acid (5 mM) markedly reduced 45Ca2+ uptake (38%: P < 0.05) but increased CK release by 85% (P < 0.001). The results demonstrate that initial elevations in muscle Na+ can facilitate increases in muscle Ca2+ and lead to alterations in muscle cell membrane integrity and CK loss. The Na+-induced increases in myocellular Ca2+ may be mediated via direct extracellular Ca2+ entry or redistribution from internal Ca2+ stores. It is proposed that in order to reduce or prevent myopathies in poultry, exposure to conditions that may lead to elevations in muscle Na+ (e.g., increased muscle activity and stress or accidental ionophore toxicosis) should be avoided. The findings of this study have implications for management strategies of bird welfare, muscle pathology, and product quality.

Acute study of interaction among cadmium, calcium, and zinc transport along the rat nephron in vivo

This study investigates the effect in rats of acute CdCl(2) (5 microM) intoxication on renal function and characterizes the transport of Ca(2+), Cd(2+), and Zn(2+) in the proximal tubule (PT), loop of Henle (LH), and terminal segments of the nephron (DT) using whole kidney clearance and nephron microinjection techniques. Acute Cd(2+) injection resulted in renal losses of Na(+), K(+), Ca(2+), Mg(2+), PO(4)(-2), and water, but the glomerular filtration rate remained stable. (45)Ca microinjections showed that Ca(2+) permeability in the DT was strongly inhibited by Cd(2+) (20 microM), Gd(3+) (100 microM), and La(3+) (1 mM), whereas nifedipine (20 microM) had no effect. (109)Cd and (65)Zn(2+) microinjections showed that each segment of nephron was permeable to these metals. In the PT, 95% of injected amounts of (109)Cd were taken up. (109)Cd fluxes were inhibited by Gd(3+) (90 microM), Co(2+) (100 microM), and Fe(2+) (100 microM) in all nephron segments. Bumetanide (50 microM) only inhibited (109)Cd fluxes in LH; Zn(2+) (50 and 500 microM) inhibited transport of (109)Cd in DT. In conclusion, these results indicate that 1) the renal effects of acute Cd(2+) intoxication are suggestive of proximal tubulopathy; 2) Cd(2+) inhibits Ca(2+) reabsorption possibly through the epithelial Ca(2+) channel in the DT, and this blockade could account for the hypercalciuria associated with Cd(2+) intoxication; 3) the PT is the major site of Cd(2+) reabsorption; 4) the paracellular pathway and DMT1 could be involved in Cd(2+) reabsorption along the LH; 5) DMT1 may be one of the major transporters of Cd(2+) in the DT; and 6) Zn(2+) is taken up along each part of the nephron and its transport in the terminal segments could occur via DMT1.