Rare earth element scandium mitigates the chromium toxicity in Lemna minor by regulating photosynthetic performance, hormonal balance and antioxidant machinery.

Chromium (Cr) toxicity is a serious problem that threatens the health of living organisms and especially agricultural production. The presence of excess Cr leads to biomass loss by causing the imbalance of biochemical metabolism and inhibiting photosynthetic activity. A new critical approach to cope with Cr toxicity is the use of the rare earth elements (REEs) as an antioxidant defence system enhancer in plants. However, the effect of scandium (Sc), which is one of the REEs, is not clear enough in Lemna minor exposed to Cr toxicity. For this purpose, the photosynthetic and biochemical effects of scandium (50 µM and 200 µM Sc) treatments were investigated in Lemna minor under Cr stress (100 µM, 200 µM and 500 µM Cr). Parameters related to photosynthesis (Fv/Fm, Fv/Fo) were suppressed under Cr stress. Stress altered antioxidant enzymes activities and hormone contents. Sc applications against stress increased the activities of superoxide dismutase (SOD), NADPH oxidase (NOX), ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), and glutathione S-transferase (GST). In addition to the antioxidant system, the contents of indole-3-acetic acid (IAA), abscisic acid (ABA) and jasmonic acid (JA) were also rearranged. However, in all treatment groups, with the provision of ascorbate (AsA) regeneration and effective hormone signaling, reactive oxygen species (ROS) retention which result in high hydrogen peroxide (H2O2) content and lipid peroxidation (TBARS) were effectively removed. Sc promoted the maintenance of cellular redox state by regulating antioxidant pathways included in the AsA-GSH cycle. Our results showed that Sc has great potential to confer tolerance to duckweed by reducing Cr induced oxidative damage, protecting the biochemical reactions of photosynthesis, and improving hormone signaling.

The preparation, biodistribution, and human's absorbed dose evaluation of Radio-Scandium-HYNIC-TOC for somatostatin-receptor-positive neuroendocrine tumors therapy by animal study.

BACKGROUND: Most of the neuroendocrine tumors (NETs) express Somatostatin receptors (SSTr), which are the main bases for the development of several radiopharmaceuticals for therapy and imaging of these types of tumors. In this study, 46 Scandium nuclide was used to label a peptide compound via hydrazinonicotinyl-Tyr3-Octreotide (HYNIC-TOC) and researched further for somatostatin-receptor NETs treatment. METHODS AND MATERIALS: The labeling procedure was conducted at 95°C for 10 min. The compound stability was tested in the environment of human serum at 37°C. The biodistribution of compound was investigated in balb/c normal mice and mice bearing AR4-2J tumor. Absorbed Doses of Human Organs were estimated by extrapolation of the biokinetics data of compound in mice to human's organs and then the absorbed doses were estimated by application of MATLAB and MIRDOSE software. RESULTS: Labeling yield was more than 90% with 555 MBq/mg specific activity. The radio-labeled compound expressed well consistency in human serum. The tumor uptake reached 3.831 ID/g% until 4 h post-injection and increased to 5.564%ID/g until 24 h post-injection. CONCLUSION: The main achievement of this study was high tumor uptake of 46 Sc-HYNIC-TOC which may be therapeutically valuable for the therapy of NETs. The estimation of the absorbed dose of human from 47 Scandium-HYNIC-TOC showed low absorbed doses in critical organs and the elimination of the radiopharmaceutical was through the gastrointestinal tract.

In Vitro Evaluation of the Squaramide-Conjugated Fibroblast Activation Protein Inhibitor-Based Agents AAZTA5.SA.FAPi and DOTA.SA.FAPi.

Recently, the first squaramide-(SA) containing FAP inhibitor-derived radiotracers were introduced. DATA5m.SA.FAPi and DOTA.SA.FAPi with their non-radioactive complexes showed high affinity and selectivity for FAP. After a successful preclinical study with [68Ga]Ga-DOTA.SA.FAPi, the first patient studies were realized for both compounds. Here, we present a new squaramide-containing compound targeting FAP, based on the AAZTA5 chelator 1,4-bis-(carboxylmethyl)-6-[bis-(carboxymethyl)-amino-6-pentanoic-acid]-perhydro-1,4-diazepine. For this molecule (AAZTA5.SA.FAPi), complexation with radionuclides such as gallium-68, scandium-44, and lutetium-177 was investigated, and the in vitro properties of the complexes were characterized and compared with those of DOTA.SA.FAPi. AAZTA5.SA.FAPi and its derivatives labelled with non-radioactive isotopes demonstrated similar excellent inhibitory potencies compared to the previously published SA.FAPi ligands, i.e., sub-nanomolar IC50 values for FAP and high selectivity indices over the serine proteases PREP and DPPs. Labeling with all three radiometals was easier and faster with AAZTA5.SA.FAPi compared to the corresponding DOTA analogue at ambient temperature. Especially, scandium-44 labeling with the AAZTA derivative resulted in higher specific activities. Both DOTA.SA.FAPi and AAZTA5.SA.FAPi showed sufficiently high stability in different media. Therefore, these FAP inhibitor agents could be promising for theranostic approaches targeting FAP.

Scandium calix[n]arenes (n = 4, 6, 8): structural, cytotoxicity and ring opening polymerization studies.

Interaction of [Sc(OR)3] (R = iPr or triflate) with p-tert-butylcalix[n]arenes, where n = 4, 6, or 8, affords a number of intriguing structural motifs, which are relatively non-toxic (cytotoxicity evaluated against cell lines HCT116 and HT-29) and a number were capable of the ring opening polymerization (ROP) of cyclohexene oxide.

Antiproliferative Properties of Scandium Exopolysaccharide Complexes on Several Cancer Cell Lines.

Antimetastatic properties on both murine and human osteosarcoma cell lines (POS-1 and KHOS) have been evidenced using exopolysaccharide (EPS) derivatives, produced by Alteromonas infernus bacterium. These derivatives had no significant effect on the cell cycle neither a pro-apoptotic effect on osteosarcoma cells. Based on this observation, these EPSs could be employed as new drug delivery systems for therapeutic uses. A theranostic approach, i.e., combination of a predictive biomarker with a therapeutic agent, has been developed notably by combining with true pair of theranostic radionuclides, such as scandium 47Sc/44Sc. However, it is crucial to ensure that, once complexation is done, the biological properties of the vector remain intact, allowing the molecular tropism of the ligand to recognize its molecular target. It is important to assess if the biological properties of EPS evidenced on osteosarcoma cell lines remain when scandium is complexed to the polymers and can be extended to other cancer cell types. Scandium-EPS complexes were thus tested in vitro on human cell lines: MNNG/HOS osteosarcoma, A375 melanoma, A549 lung adenocarcinoma, U251 glioma, MDA231 breast cancer, and Caco2 colon cancer cells. An xCELLigence Real Cell Time Analysis (RTCA) technology assay was used to monitor for 160 h, the proliferation kinetics of the different cell lines. The tested complexes exhibited an anti-proliferative effect, this effect was more effective compared to EPS alone. This increase of the antiproliferative properties was explained by a change in conformation of EPS complexes due to their polyelectrolyte nature that was induced by complexation. Alterations of both growth factor-receptor signaling, and transmembrane protein interactions could be the principal cause of the antiproliferative effect. These results are very promising and reveal that EPS can be coupled to scandium for improving its biological effects and also suggesting that no major structural modification occurs on the ligand.

Predominant cleavage of proteins N-terminal to serines and threonines using scandium(III) triflate.

Proteolytic digestion prior to LC-MS analysis is a key step for the identification of proteins. Digestion of proteins is typically performed with trypsin, but certain proteins or important protein sequence regions might be missed using this endoproteinase. Only few alternative endoproteinases are available and chemical cleavage of proteins is rarely used. Recently, it has been reported that some metal complexes can act as artificial proteases. In particular, the Lewis acid scandium(III) triflate has been shown to catalyze the cleavage of peptide bonds to serine and threonine residues. Therefore, we investigated if this compound can also be used for the cleavage of proteins. For this purpose, several single proteins, the 20S immune-proteasome (17 proteins), and the Universal Proteomics Standard UPS1 (48 proteins) were analyzed by MALDI-MS and/or LC-MS. A high cleavage specificity N-terminal to serine and threonine residues was observed, but also additional peptides with deviating cleavage specificity were found. Scandium(III) triflate can be a useful tool in protein analysis as no other reagent has been reported yet which showed cleavage specificity within proteins to serines and threonines.

Comparison between Three Promising ß-emitting Radionuclides, (67)Cu, (47)Sc and (161)Tb, with Emphasis on Doses Delivered to Minimal Residual Disease.

PURPOSE: Radionuclide therapy is increasingly seen as a promising option to target minimal residual disease. Copper-67, scandium-47 and terbium-161 have a medium-energy ß(-) emission which is similar to that of lutetium-177, but offer the advantage of having diagnostic partner isotopes suitable for pretreatment imaging. The aim of this study was to compare the efficacy of (67)Cu, (47)Sc and (161)Tb to irradiate small tumors. METHODS: The absorbed dose deriving from a homogeneous distribution of (67)Cu, (47)Sc or (161)Tb in water-density spheres was calculated with the Monte Carlo code CELLDOSE. The diameters of the spheres ranged from 5 mm to 10 µm, thus simulating micrometastases or single tumor cells. All electron emissions, including ß(-) spectra, Auger and conversion electrons were taken into account. Because these radionuclides differ in electron energy per decay, the simulations were run assuming that 1 MeV was released per µm(3), which would result in a dose of 160 Gy if totally absorbed. RESULTS: The absorbed dose was similar for the three radionuclides in the 5-mm sphere (146-149 Gy), but decreased differently in smaller spheres. In particular, (161)Tb delivered higher doses compared to the other radionuclides. For instance, in the 100-µm sphere, the absorbed dose was 24.1 Gy with (67)Cu, 14.8 Gy with (47)Sc and 44.5 Gy with (161)Tb. Auger and conversion electrons accounted for 71% of (161)Tb dose. The largest dose differences were found in cell-sized spheres. In the 10-µm sphere, the dose delivered by (161)Tb was 4.1 times higher than that from (67)Cu and 8.1 times that from (47)Sc. CONCLUSION: (161)Tb can effectively irradiate small tumors thanks to its decay spectrum that combines medium-energy ß(-) emission and low-energy conversion and Auger electrons. Therefore (161)Tb might be a better candidate than (67)Cu and (47)Sc for treating minimal residual disease in a clinical setting.

Undecaprenyl pyrophosphate involvement in susceptibility of Bacillus subtilis to rare earth elements.

The rare earth element scandium has weak antibacterial potency. We identified a mutation responsible for a scandium-resistant phenotype in Bacillus subtilis. This mutation was found within the uppS gene, which encodes undecaprenyl pyrophosphate synthase, and designated uppS86 (for the Thr-to-Ile amino acid substitution at residue 86 of undecaprenyl pyrophosphate synthase). The uppS86 mutation also gave rise to increased resistance to bacitracin, which prevents cell wall synthesis by inhibiting the dephosphorylation of undecaprenyl pyrophosphate, in addition to enhanced amylase production. Conversely, overexpression of the wild-type uppS gene resulted in increased susceptibilities to both scandium and bacitracin. Moreover, the mutant lacking undecaprenyl pyrophosphate phosphatase (BcrC) showed increased susceptibility to all rare earth elements tested. These results suggest that the accumulation of undecaprenyl pyrophosphate renders cells more susceptible to rare earth elements. The availability of undecaprenyl pyrophosphate may be an important determinant for susceptibility to rare earth elements, such as scandium.

Chemical and biological evaluation of 153 Sm and 46/47 Sc complexes of indazolebisphosphonates for targeted radiotherapy.

INTRODUCTION: Novel 1-hydroxy-1,1-bisphosphonates derived from indazole and substituted at the C-3 position were labeled with the radionuclides (46)Sc and (153)Sm. Several parameters such as molar ligand concentration, pH, reaction time and temperature were studied. The radiolabelling yield, reaction kinetics and stability were assessed and radiocomplexes were evaluated by in vitro and in vivo experiments. METHODS: The radionuclides (46)Sc and (153)Sm were obtained by neutron irradiation of natural Sc(2)O(3) and enriched (152)Sm(2)O(3) (98.4%) targets at the neutron flux of 3 × 10(14) n cm(-2)s(-1). The radiolabelling yield, reaction kinetics and stability were accomplished by ascending instant thin layer chromatography. The radiocomplexes were submitted to in vitro experiments (hydroxyapatite binding and lipophilicity) and biodistribution studies in animal models. RESULTS: The radionuclides (46)Sc and (153)Sm were produced with specific activities of 100 and 430 MBq mg(-1), respectively. High radiochemical yields were achieved and the hydrophilic radiocomplexes have shown high degree of binding to hydroxyapatite. Biodistribution studies at 1, 3 and 24h of the 4 radiocomplexes under study, have showed a similar biodistribution profile with a relatively high bone uptake, slow clearance from blood and a very slow rate of total radioactivity excretion from the whole animal body. CONCLUSION: We have developed a new class of indazolebisphosphonates complexes with radioisotopes of samarium and scandium. All complexes have shown high degree of binding to hydroxyapatite, which could be attributed to the ionized phosphonate groups. The bone uptake and the bone-to-muscle ratios were relatively low.

Rare earth elements activate the secondary metabolite-biosynthetic gene clusters in Streptomyces coelicolor A3(2).

Genome sequencing projects have revealed many biosynthesis gene clusters for the production of as-yet unknown secondary metabolites, especially in actinomycetes. Here, we report that the rare earth elements, scandium and/or lanthanum, markedly activate, ranging from 2.5- to 12-fold, the expression of nine genes belonging to nine secondary metabolite-biosynthetic gene clusters of Streptomyces coelicolor A3(2) when added to the medium at low concentrations. HPLC analysis of ethyl acetate-extractable metabolites indicated the detectability of several compounds only in the rare earth-treated cultures. This approach should facilitate discovery of new biologically active compounds and the study of secondary metabolite production.

The rare earth, scandium, causes antibiotic overproduction in Streptomyces spp.

Despite their importance in the chemical industry, the significance of rare earths in biology has been largely overlooked. Here, it is reported that the rare earth, scandium (Sc), causes antibiotic overproduction by 2-25-fold when added at a low concentration (10-100 microM) to cultures of Streptomyces coelicolor A3(2) (actinorhodin producer), Streptomyces antibioticus (actinomycin producer), and Streptomyces griseus (streptomycin producer). Not just for enhancement of antibiotic production, scandium was also effective in activating the dormant ability to produce actinorhodin in Streptomyces lividans. The effects of scandium were exerted at the level of transcription of pathway-specific positive regulatory genes, as demonstrated by marked up-regulation of actII-ORF4 in S. coelicolor cells exposed to this element. The bacterial alarmone, guanosine 5'-diphosphate 3'-diphosphate, was essential for actinorhodin overproduction provoked by scandium.

Inhibition of transiently expressed low- and high-voltage-activated calcium channels by trivalent metal cations.

Calcium channels are important regulators of neuronal excitability and contribute to transmitter release, calcium dependent gene expression, and oscillatory behavior in many cell types. Under physiological conditions, native low-voltage (T-type)- and high-voltage-activated (HVA) currents are potently inhibited by trivalent cations. However, the presence of multiple calcium channel isoforms has hampered our ability to unequivocally assess the effects of trivalent cations on channel activity. Here, we describe the actions of nine trivalent metal ions on transiently expressed alpha1G (Cav3.1) T-type calcium channels cloned from human brain. In 2 mM external barium solution, yttrium most potently inhibited alpha1G current (IC50 = 28 nM), followed by erbium > gadolinium ~ cerium > holmium > ytterbium > neodymium > lanthanum >> scandium. With the exception of scandium, blocking affinity was loosely correlated with decreasing ionic radius. A detailed characterization of yttrium block revealed a 25-fold decrease in blocking affinity when the external concentration of charge carrier was increased from 2 mM to 20 mM. In 20 mM barium, yttrium also effectively inhibited various types of cloned HVA channels indicating that this ion is a nonselective blocker. For all calcium channels examined, yttrium preferentially inhibited inward over outward current, but block was otherwise voltage independent. In addition to peak current inhibition, P/Q- and L-type channels underwent a unique speeding of the macroscopic time course of inactivation. Whereas peak current block of alpha1A channels was highly sensitive to the external charge carrier concentration, the inactivation effects mediated by yttrium were not, suggesting that the two effects are due to distinct mechanisms. Moreover, the speeding effect was greatly attenuated by manipulations that slowed the inactivation kinetics of the channels. Thus, our evidence suggests that yttrium effects are mediated by two distinct events: peak current block likely occurring by occlusion of the pore, and kinetic speeding arising from yttrium interactions with the channel that alter the state of the inactivation gate.

[Chemiluminescence suppression in roots of Pisum sativum L. by various metal ions]. / Podavlenie khemiliuminestsentsii kornei Pisum sativum L. ionami nekotorykh metallov.

The effect of rare metal ions on the activity of the peroxidase system in Pisum sativum L. roots was studied by luminol-dependent chemiluminescence. Trivalent ions of scandium, gallium, indium, and lanthanum, to different extents, inhibit the chemiluminescence of damaged P. sativum roots. A decreased generation of superoxide due to the formation of the complex between metal ions and NADP can underlie the inhibited activity of peroxidase system. The possible mechanism of inhibition of the peroxidase system activity by metal ions is discussed.

New probes of the F1-ATPase catalytic transition state reveal that two of the three catalytic sites can assume a transition state conformation simultaneously.

MgADP in combination with fluoroscandium (ScFx) is shown to form a potently inhibitory, tightly bound, noncovalent complex at the catalytic sites of F(1)-ATPase. The F(1).MgADP.ScFx complex mimics a catalytic transition state. Notably, ScFx caused large enhancement of MgADP binding affinity at both catalytic sites 1 and 2, with little effect at site 3. These results indicate that sites 1 and 2 may form a transition state conformation. A new direct optical probe of F(1)-ATPase catalytic transition state conformation is also reported, namely, substantial enhancement of fluorescence emission of residue beta-Trp-148 observed upon binding of MgADP.ScFx or MgIDP. ScFx. Using this fluorescence signal, titrations were performed with MgIDP.ScFx which demonstrated that catalytic sites 1 and 2 can both form a transition state conformation but site 3 cannot. Supporting data were obtained using MgIDP-fluoroaluminate. Current models of the MgATP hydrolysis mechanism uniformly make the assumption that only one catalytic site hydrolyzes MgATP at any one time. The fluorometal analogues demonstrate that two sites have the capability to form the transition state simultaneously.

Modification of radiation sensitivity by salts of the metals beryllium and indium and the rare earths cerium, lanthanum and scandium.

The LD50 of 46 salts of metals and rare earths (lanthanoids) was determined in mice. Half the LD50 of the compounds was then combined with lethal radiation (10.5 Gy) and the modification of survival time was scored. Only the metals beryllium and indium and the rare earths cerium, lanthanum and scandium displayed activity in our assay. They were then tested at a wider range of lower doses and reduced survival time in a dose-dependent fashion. This appears to be compatible with enhancement of radiation sensitivity. The interaction of these metals and rare earths with radiation adds a new facet to their toxicological spectrum and, by enhancing radiation effects, may influence estimates of risk. On the other hand, the radiosensitizing properties of the metals may be useful for further development of compounds to be used as adjuncts in specific situations of cancer radiotherapy.

Alpha-latrotoxin: preparation and effects on calcium fluxes.

A toxin that causes a massive presynaptic activation of transmitter release from nerve terminals is alpha-latrotoxin, isolated from Latrodectus tredecimguttatus spider venom. This toxin has been highly purified, utilizing as a biological assay a toxin-dependent increase in 45Ca(2+)-accumulation by PC12 cells. The purification protocol includes an ion-exchange step and a gel-filtration column, by fast-flow liquid chromatography. The resulting toxin is a polypeptide of about 125 kDa in molecular mass. At nmol concentrations it specifically activates calcium influx and transmitter secretion after interacting with neuronal acceptors of the presynaptic membrane. The inhibitory effect of trivalent ions (which may develop as degradation product of 45Ca2+) on toxin-dependent calcium accumulation by PC12 cells is described. The results obtained suggest that calcium fluxes directly involved in the neurosecretory event, may occur through newly formed toxin-dependent channels.

The behavior of the ouabain-insensitive sodium efflux in single barnacle muscle fibers toward the microinjection of aluminum.

Recent work with single muscle fibers from the barnacle Balanus nubilus has shown that the injection of Al into these fibers leads to inhibition of the resting Na efflux and that this involves both the ouabain-sensitive and the ouabain-insensitive components of the efflux. This work also showed that the injection of Al into ouabain-poisoned fibers often leads to a rise in the remaining Na efflux. This observation suggested the possibility that Al is able to stimulate the ouabain-insensitive Na by increasing myoplasmic free Ca2+ and that trigger Ca2+ reaches the myoplasm via voltage-dependent Ca2+ channels. The results obtained are as follows: (i) The injection of AlCl3 into fibers poisoned with ouabain produces a biphasic or monophasic effect on the remaining Na efflux. That is, stimulation is followed by inhibition, or there is only stimulation. (ii) This response is dose-dependent and is seen to take place following the injection of Al in a concentration as low as 0.01 M. (iii) Both Ga3+ and Sc3+ are able to mimic the effect of Al. (iv) Injection of EGTA following peak stimulation of the ouabain-insensitive Na efflux by injected AlCl3 leads to reversal of this response. If, however, EGTA is injected long after the onset of peak stimulation and after ouabain reaches its maximum effect, it is found to be ineffective. (v) The magnitude of the stimulatory response of the ouabain-insensitive Na efflux is a sigmoidal function of external Ca2+ and is almost completely abolished by verapamil, devapamil, and Cd2+ but is unaffected by injecting Mg2+ before or after AlCl3. (vi) Whereas preinjection of Al reduces the response to ryanodine, external preapplication of ryanodine fails to alter the response to Al. The preinjection of deferoxamine (a potent chelator of Al) fails to stop the stimulatory response to Al injection from occurring. Taken together, these findings support the hypothesis that the stimulatory response elicited by Al injection is due to a fall in myoplasmic pCa resulting from activation of voltage-dependent Ca2+ channels and that it involves the operation of the Na+-Ca2+ exchanger in the reverse mode.

Activation and inactivation of bovine caudate acetylcholinesterase by trivalent cations.

Kinetic analysis of the interaction of trivalent cations with mammalian brain acetylcholinesterase revealed at least three distinct concentration-dependent effects on enzyme activity. Acetylcholinesterase was purified from bovine caudate nucleus by affinity chromatography to a specific activity of 1.1 mmoles acetylthiocholine X hr-1 X (mg protein)-1. The cations studied included the chloride salts of lanthanum, terbium, yttrium and scandium in low and high ionic strength buffers (2 mM Pipes +/- 0.1 M NaCl). At low ionic strength, high affinity noncompetitive or allosteric activation was observed at very low cation concentrations (1-10 microM); at higher concentrations (50-200 microM) these cations were noncompetitive inhibitors; and at 200-500 microM they exerted a mixed competitive-noncompetitive inhibition. Activation by low cation concentrations was not evident in high ionic strength buffers, while enzyme inhibition by all the trivalent cations was similar at low and high ionic strength. Inhibition by all of the multivalent cations was fully reversed by a 10-fold excess of EDTA or by a 100-fold dilution of the inhibited enzyme. The water-soluble carboxyl group affinity reagent, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide, was shown to specifically block the activating effect of the multivalent cations supporting the suggestion that the beta- or "activator" peripheral anionic sites (P1) involve a carboxyl group outside the enzyme active site.

Hormone-sensitive magnesium transport in murine S49 lymphoma cells: characterization and specificity for magnesium.

1. The hormone-sensitive transport of Mg(2+) into murine S49 lymphoma cells and its relationship to other divalent cation transport systems have been investigated.2. Mg(2+) influx, measured with (28)Mg(2+), is saturable with an apparent extracellular ion concentration at half-maximal influx (K(in)) for Mg(2+) of 330 muM and a maximal influx rate of 360 p-mole/min.10(7) cells (2.9 n-mole/min.mg cell protein or a flux rate of about 0.12 p-mole/sec.cm(2)). Efflux of Mg(2+) is biphasic with half-times of 55 and 240 min at 37 degrees C and is temperature-sensitive.3. beta-Adrenergic agonists inhibit influx but not efflux of Mg(2+) in S49 cells. Efflux of Mg(2+) is also unaffected by extracellular [Mg(2+)] or [Ca(2+)]. These results imply that the mechanism of the transport system does not involve Mg-Mg exchange.4. Mn(2+) is a non-competitive inhibitor of Mg(2+) influx with an inhibition constant, K(i), of about 200 muM. The weak inhibition exhibited by Ca(2+) (K(i) > 5 mM) is also non-competitive. La(3+) inhibits Mg(2+) transport half-maximally at about 100 muM; Ni(2+), Zn(2+), Co(2+) and Sc(3+) are all less effective than La(3+). The Ca(2+)-channel blockers cis-diltiazem, verapamil, and nifedipine and the monovalent cations Na(+) and K(+) also have no effect on Mg(2+) influx. However, increasing the extracellular pH stimulates Mg(2+) influx.5. Total cellular Mg(2+) is about 85 n-mole/10(7) cells; however, at apparent isotopic equilibrium with (28)Mg(2+) less than 3% of total cellular Mg(2+) has been exchanged. This indicates that cellular Mg(2+) is highly compartmented and that recently transported Mg(2+) exchanges very slowly with bulk intracellular Mg(2+).6. Ca(2+) influx has a K(in) of 80 muM and is much slower than Mg(2+) influx. V(max) varied in different experiments from 3 to 15 p-mole/min.10(7) cells (25-125 p-mole/min.mg cell protein). Efflux of Ca(2+) is biphasic with half-times of 22 and 200 min and is temperature-sensitive. Hormonal stimulation has no effect on either influx or efflux of Ca(2+). Mg(2+) is a competitive inhibitor of Ca(2+) influx (K(i) = 3 mM).7. Two kinetic components of Mn(2+) influx are present with apparent K(in)s of 4 muM and 100 muM. Maximal influx rates are 5 and 60 p-mole/min.10(7) cells (40 and 480 p-mole/min.mg cell protein), respectively. Influx of Mn(2+) is not altered by beta-adrenergic agonist.8. Uptake of Na(+) or K(+) is unaltered by beta-adrenergic stimulation. These data in the S49 lymphoma cell indicate that (a) Mg(2+) is translocated by a transport system independent of those that transport other divalent cations, (b) hormonal inhibition of divalent ion transport is specific for Mg(2+) and (c) cellular Mg(2+) is highly compartmented.