Acute effect of oral phosphate loading on serum fibroblast growth factor 23 levels in healthy men

Serum fibroblast growth factor 23 (FGF23) is a novel phosphaturic factor and important for the regulation of inorganic phosphate (Pi) homeostasis. In this study, we examined an acute effect of oral Pi loading on serum FGF23 levels to clarify the role in rapid adjustment of serum Pi level. We performed a randomized, double-blind, crossover study in eight healthy male volunteers. The subjects were alternately served one of three test meals containing different Pi amounts (400 mg (P400), 800 mg (P800), and 1200 mg (P1200)) as lunch at noon. The postprandial changes in serum levels of Pi, Ca, 1,25-dihydroxyvitamin D, intact-parathyroid hormone (iPTH), intact-FGF23 (iFGF23), and urinary excretion of Pi and Ca until 8 h after Pi loading were estimated. Serum Pi levels and urinary Pi excretion significantly increased within 1 h after P400 and P800 intake. Serum iPTH levels at 1-2 and 4-6 h after P1200 intake was significantly higher than those of P400 intake. Serum iFGF23 levels slightly decreased up to 8 h after P400 intake and up to 6 h after P800 intake, but not changed in P1200 intake. Significant increase of iFGF23 was observed at 8 h after P1200 intake compared with both P400 and P800 intake. Additionally, negative association was detected between iFGF23 and serum Pi, whereas positive association was observed between iPTH and serum Pi during the short period. We conclude that oral Pi loading cannot rapidly increase serum FGF23 level. FGF23 may be not associated with rapid adaptation of Pi homeostasis.

Effect of late evening snack with rice ball on energy metabolism in liver cirrhosis

OBJECTIVE

This study investigates the effects of a late evening snack (LES), of 200 kcal of rice ball, on energy metabolism in cirrhotic patients. Impaired nutritional metabolism has been associated with cirrhosis, and frequent intake of small meals may prevent early-onset starvation, and maintain nourishment in these patients.

SUBJECTS

Twenty-one cirrhotic patients and 26 control subjects (Control) were recruited for this study. Patients were subsequently treated by LES (LC-LES) and by a non-LES regimen (LC-NLES).

METHOD

Resting energy expenditure and respiratory quotient (RQ) were assessed by indirect calorimetry at 0830, 1130 and 1430. Blood glucose and non-esterified fatty acids (NEFA) were measured just before the energy metabolism measurements. The regular diet included three major meals and LES, at 0900, 1200, 1800 and 2100, respectively. The Control and LC-NLES groups received only the major meals, whereas the LC-LES group received three meals plus 200 kcal LES for 7 days. There was no difference in the total energy intake among Control, LC-NLES and LC-LES groups.

RESULTS

Respiratory quotient in LC-NLES was significantly lower than that of Control at 0830. Respiratory quotient value in LC-LES significantly elevated from that in LC-NLES. The RQ values did not differ among Control, LC-NLES and LC-LES at 2 h after the meal (1130 and 1430). Non-esterified fatty acids in LC-LES were lower than that in LC-NLES after overnight fasting.

CONCLUSIONS

The ingestion of a 200 kcal rice ball LES can improve the nutritional metabolism in cirrhotic patients.

[Parathyroid hormone-mediated regulation of renal phosphate co-transporter]

The key player in proximal tubular Pi reabsorption, the type IIa Na(+)/Pi co-transporter, is internalized upon PTH treatment and degraded in the lysosomes. PTH action is initiated by apically and basolaterally localized PTH receptors, whereby apical effects are most probably via cAMP-independent (via PKC) and basolateral effects via cAMP-dependent (via PKA) regulatory mechanisms. The molecular determinants at the level of the transporter protein or at the level of interacting (regulatory) proteins are not yet known.

Human L-type amino acid transporter 1 (LAT1): characterization of function and expression in tumor cell lines

System L is a major nutrient transport system responsible for the transport of large neutral amino acids including several essential amino acids. We previously identified a transporter (L-type amino acid transporter 1: LAT1) subserving system L in C6 rat glioma cells and demonstrated that LAT1 requires 4F2 heavy chain (4F2hc) for its functional expression. Since its oncofetal expression was suggested in the rat liver, it has been proposed that LAT1 plays a critical role in cell growth and proliferation. In the present study, we have examined the function of human LAT1 (hLAT1) and its expression in human tissues and tumor cell lines. When expressed in Xenopus oocytes with human 4F2hc (h4F2hc), hLAT1 transports large neutral amino acids with high affinity (K(m)= approximately 15- approximately 50 microM) and L-glutamine and L-asparagine with low affinity (K(m)= approximately 1.5- approximately 2 mM). hLAT1 also transports D-amino acids such as D-leucine and D-phenylalanine. In addition, we show that hLAT1 accepts an amino acid-related anti-cancer agent melphalan. When loaded intracellularly, L-leucine and L-glutamine but not L-alanine are effluxed by extracellular substrates, confirming that hLAT1 mediates an amino acid exchange. hLAT1 mRNA is highly expressed in the human fetal liver, bone marrow, placenta, testis and brain. We have found that, while all the tumor cell lines examined express hLAT1 messages, the expression of h4F2hc is varied particularly in leukemia cell lines. In Western blot analysis, hLAT1 and h4F2hc have been confirmed to be linked to each other via a disulfide bond in T24 human bladder carcinoma cells. Finally, in in vitro translation, we show that hLAT1 is not a glycosylated protein even though an N-glycosylation site has been predicted in its extracellular loop, consistent with the property of the classical 4F2 light chain. The properties of the hLAT1/h4F2hc complex would support the roles of this transporter in providing cells with essential amino acids for cell growth and cellular responses, and in distributing amino acid-related compounds.

Molecular events involved in up-regulating human Na+-independent neutral amino acid transporter LAT1 during T-cell activation

We investigated the regulation of system-L amino acid transporter (LAT1) during T-cell activation. In quiescent T-cells, L-leucine transport is mediated mainly by the system-L amino acid transport system and is increased significantly during T-cell activation by PMA and ionomycin. In quiescent T-cells, the LAT1 protein was heterocomplexed with 4F2 heavy chain (4F2hc) in the plasma membrane. During T-cell activation, the amounts of 4F2hc and LAT1 heterocomplex were significantly elevated compared with those in quiescent T-cells. In addition, by Northern-blot analysis, these increments were found to be due to elevated levels of LAT1 and 4F2hc mRNA. Transient expression of constructs comprising various LAT1 gene promoter fragments, which contained all three of the GC boxes, was sufficient for promoting luciferase expression in Jurkat T-cells, but the promoter of the LAT1 gene did not respond to PMA and ionomycin. Similar observations were observed in the human 4F2hc gene promoter. In nuclear run-on assay, the LAT1 and 4F2hc genes were actively transcribed even in quiescent T-cells, but the low levels of both transcripts were shown to be the result of a block to transcription elongation within the exon 1 intron 1 regions. These findings indicated that a removal of the block to mRNA elongation stimulates the induction of system-L amino acid transporter gene transcripts (LAT1 and 4F2hc) in activated T-cells.

A neutrophil elastase inhibitor (ONO-5046) reduces neurologic damage after spinal cord injury in rats

In view of a cytoprotective effect of elastase inhibitor on chemokine-mediated tissue injury, we examined the neuroprotective effect of ONO-5046, a specific inhibitor of neutrophil elastase, in rats with spinal cord injury. Standardized spinal cord compression markedly increased cytokine-induced neutrophil chemo-attractant (CINC)-1 mRNA and protein. Their increases correlated with neurologic severity of injured rats. Immunohistochemically, CINC-1 protein was detected sequentially in vascular endothelial cells at 4 h, in perivascular neutrophils at 8 h, and in neutrophils infiltrating into cord substance at 12 h. Pretreatment with ONO-5046 (50 mg/kg) markedly ameliorated motor disturbance in injured rats, and reduced CINC-1 protein and mRNA expression. ONO-5046 also significantly reduced the increase of neutrophil accumulation or infiltration estimated by myeloperoxidase activity, and the extent of vascular permeability by Evans blue extravasation in the injured cord segment in comparison to control animals receiving vehicle. These results suggest that CINC-1 contributed to inflammation in rat spinal cord injury and ONO-5046 attenuated neurologic damage partly by blocking CINC-1 production of the chemoattractant, preventing neutrophil activation and vascular endothelial cell injury.

The polymorphism in the caudal-related homeodomain protein Cdx-2 binding element in the human vitamin D receptor gene

The major physiological activity of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] is the regulation of calcium absorption in the small intestine, and the level of vitamin D receptor (VDR) is an important factor in this regulation. In a previous study, we indicated-that the caudal-related homeodomain Cdx-2 played an important role in the intestine-specific transcription of the human VDR gene. In this study, the polymorphism was identified in the core sequence 5'-ATAAAAACTTAT-3' in the Cdx-2 binding site in the VDR gene promoter. In 261 Japanese women with genotyped VDR polymorphisms, 48 were genotype Cdx-A (adenine at -3731 nucleotides [nt] relative to the transcription start site of human VDR gene 5-ATAAAAACTTAT), 82 were genotype Cdx-G (guanine at -3731 nt, 5'-GTAAAAACTTAT-3'), and 131 were genotype Cdx-A/G (heterozygote). In postmenopausal Japanese women, the bone mineral density (BMD) in the lumbar spine (L2-L4) with the Cdx-G homozygote was 12% lower than that with the Cdx-A homozygote (p < 0.05). In electrophoretic gel mobility shift assay (EMSA), the oligonucleotide with Cdx-G allele markedly decreased the binding to Cdx-2 compared with that in the Cdx-A allele. The transcriptional activity of the VDR promoter with Cdx-G allele was decreased to 70% of the Cdx-A allele. In addition, in the herpes simplex virus thymidine kinase promoter, the Cdx-2 binding element with the G allele showed significantly lower transcriptional activity than that of the A allele. Thus, the polymorphism in the Cdx-2 binding site of the VDR gene (Cdx-polymorphism) would affect the expression of VDR in the small intestine. In addition, this polymorphism may modulate BMD in postmenopausal Japanese women.

[Occupational risk of acquiring tuberculosis among hospital nursing personnel]

At hospitals, patients with tuberculosis are attended by several professionals and among them nursing workers. These workers are subjected to the risk of the tuberculosis infection. This study had the objective of investigating the number of nursing workers in a hospital that acquired tuberculosis in a pre-determined period and their general characteristics; to calculate the morbidity coefficient of this disease and discuss the occupational risk among these workers. In one year, health workers presented 3.86 times greater risk, and, in another year, 1.47 times greater risk. In the present study tuberculosis was considered an occupational hazard for hospital nursing workers.

Identification and functional analysis of three isoforms for the Na+-dependent phosphate co-transporter (NaPi-2) in rat kidney

We have isolated three unique NaPi-2-related protein cDNAs (NaPi-2alpha, NaPi-2beta and NaPi-2gamma) from a rat kidney library. NaPi-2alpha cDNA encodes 337 amino acids which have high homology to the N-terminal half of NaPi-2 containing three transmembrane domains. NaPi-2beta encodes 327 amino acids which are identical to the N-terminal region of NaPi-2 containing four transmembrane domains, whereas the 146 amino acids in the C-terminal region are completely different. In contrast, NaPi-2gamma encodes 268 amino acids which are identical to the C-terminal half of NaPi-2. An analysis of phage and cosmid clones indicated that the three related proteins were produced by alternative splicing in the NaPi-2 gene. In a rabbit reticulocyte lysate system, NaPi-2alpha, beta and gamma were found to be 36, 36 and 29 kDa polypeptides, respectively. NaPi-2alpha and NaPi-2gamma were glycosylated and revealed to be 45 and 35 kDa proteins, respectively. A functional analysis demonstrated that NaPi-2gamma and alpha markedly inhibited NaPi-2 activity in Xenopus oocytes. The results suggest that these short isoforms may function as a dominant-negative inhibitor of the full-length transporter.

Hypophosphatemic rickets accompanying McCune-Albright syndrome: evidence that a humoral factor causes hypophosphatemia

McCune-Albright syndrome (MAS) is sometimes complicated by hypophosphatemia. However, it remains unclear whether a humoral factor is associated with the cause of hypophosphatemia. We isolated cells with mutations of the Gsalpha gene from fibrous bone dysplasia tissues of two MAS patients (MAS cells). Severe combined immunodeficiency (SCID) mice were subjected to experiments using from one of these cells patients. Effects of conditioned media (CM) isolated from MAS cells (MAS-CM) on phosphate transport were investigated by using rat renal slices, the renal cell line OK-B, rat intestinal rings and the human intestinal cell line Caco-2. In addition, the effects of MAS-CM on human sodium-dependent phosphate transporter (NPT2) gene promoter activity expression were investigated in the renal cell line OK-B2400 and were compared with the effects of CM isolated from a patient with oncogenic hypophosphatemic osteomalacia (OHO). MAS cells caused significant hypophosphatemia (P < 0.05) and elevated serum alkaline phosphatase activity (P < 0.05) in SCID mice. The MAS-CM significantly inhibited phosphate uptake in everted intestinal rings (P < 0.01), whereas it had no effect on glucose uptake. The MAS-CM had no effect on either phosphate uptake in the kidney or NPT2 gene promoter activity. In contrast, the CM of the OHO patient significantly inhibited phosphate uptake and NPT2 gene promoter activity. These results indicate that the humoral factor derived from fibrous dysplasia cells of the MAS patient is different to that from OHO patients, because the humoral factor from the MAS patient inhibited phosphate transport not in the kidney but in the intestine.

Association between two types of vitamin d receptor gene polymorphism and bone status in premenopausal Japanese women

Polymorphisms in the vitamin D receptor (VDR) gene using ultrasound (US) bone mass and bone metabolic markers were investigated as potential genetic markers for osteoporosis in 126 premenopausal Japanese women aged 27.2 +/- 10.1 (mean +/- SD) years. The relationship between their VDR gene polymorphisms and bone states was determined. VDR genotypes were based on the absence (B) or presence (b) of the Bsm I restriction site (B polymorphism), and ATG (the M allele) and ACG (the m allele) sequences at the translation initiation site (M polymorphism). Genotype frequencies were 73.8%, bb; 24.6%, Bb; 1.6%, BB; 15.1%, MM; 51.6%, Mm and 33.3%, mm. The stiffness index of calcaneal bone minerals measured by an US bone densitometer was significantly higher in the mm types (P <0.05 versus MM) than in the Mm types (P <0.01 versus MM) and MM types. There was no significant difference between in B polymorphisms. Furthermore, bone mass was correlated with serum bone type alkaline phosphatase (ALP) activity and urinary deoxypyridinoline concentration in M polymorphisms. Because the distribution of B polymorphisms in each M polymorphism genotype did not differ, M polymorphisms were affected independently from B polymorphisms to bone mass or bone metabolic markers. No significant difference was observed in nutritional intake and food consumption among genotypes. In the MM and Mm types, the bone mass was closely related to the frequency of milk intake during the periods of elementary and junior high school. In contrast, bone mass was not associated with nutritional intake or the frequency of past milk intake in B polymorphisms. Therefore, the M polymorphism of the VDR gene is a stronger genetic indicator of osteoporosis than the B polymorphism in premenopausal Japanese woman.

Inhibition of repair of radiation-induced DNA double-strand breaks by nickel and arsenite

The effect of arsenite or nickel on the repair of DNA double-strand breaks (DSBs) was studied in gamma-irradiated Chinese hamster ovary cells using pulsed-field gel electrophoresis. After treatment with nickel chloride or arsenite for 2 h, cells were irradiated with gamma rays at a dose of 40 Gy, and the numbers of DNA DSBs were measured immediately after irradiation as well as at 30 min postirradiation. Both arsenite and nickel(II) inhibited repair of DNA DSBs in a concentration-dependent manner; 0.08 mM arsenite significantly inhibited the rejoining of DSBs, while 76 mM nickel was necessary to observe a clear inhibition. The mean lethal concentrations for the arsenite and nickel(II) treatments were approximately 0.12 and 13 mM, respectively. This indicates that the inhibition of repair by arsenite occurred at a concentration at which appreciable cell survival occurred, but that nickel(II) inhibited repair only at cytotoxic concentrations at which the cells lost their proliferative ability. These novel observations provide insight into the mechanisms underlying the effects of combined exposure to arsenite and ionizing radiation in our environment.

A newly identified lipoprotein lipase (LPL) gene mutation (F270L) in a Japanese patient with familial LPL deficiency

We have systematically investigated the molecular defects resulting in a primary lipoprotein lipase (LPL) deficiency in a Japanese male infant (proband SH) with fasting hyperchylomicronemia. Neither LPL activity nor immunoreactive LPL mass was detected in pre- or postheparin plasma from proband SH. DNA sequence analysis of the LPL gene of proband SH revealed homozygosity for a novel missense mutation of F270L (Phe(270)-->Leu/TTT(1065)-->TTG) in exon 6. The function of the mutant F270L LPL was determined by both biochemical and immunocytochemical studies. In vitro expression experiments on the mutant F270L LPL cDNA in COS-1 cells demonstrated that the mutant LPL protein was synthesized as a catalytically inactive form and its total amount was almost equal to that of the normal LPL. Moreover, the synthesized mutant LPL was non-releasable by heparin because the intracellular transport of the mutant LPL to the cell surface - by which normal LPL becomes heparin-releasable - was impaired due to the abnormal structure of the mutant LPL protein. These findings explain the failure to detect LPL activities and masses in pre- and postheparin plasma of the proband. The mutant F270L allele generated an XcmI restriction enzyme site in exon 6 of the LPL gene. The carrier status of F270L in the proband's family members was examined by digestion with XcmI. The proband was ascertained to be homozygous for the F270L mutation and his parents and sister were all heterozygous. The LPL activities and masses of the parents and the sister (carriers) were half or less than half of the control values. Regarding the phenotype of the carriers, the mother with a sign of hyperinsulinemia manifested hypertriglyceridemia (type IV hyperlipoproteinemia), whereas the healthy father and the sister were normolipidemic. Hyperinsulinemia may be a strong determinant of hypertriglyceridemia in subjects with heterozygous LPL deficiency.

Effects of alendronate on bone metastases and hypercalcemia after surgery for hepatocellular carcinoma

Alendronate, a bisphosphonate compound, lowers serum calcium in patients with cancer-associated hypercalcemia through its inhibitory effect on bone resorption and as a result symptoms associated with hypercalcemia improve. This study was carried out to investigate the effects of alendronate in patients with hypercalcemia due to bone metastasis of hepatocellular carcinoma (HCC). Two patients were evaluated. Their corrected serum calcium and alpha-fetoprotein (AFP) levels and their computed tomography (CT), bone scintigraphy and magnetic resonance imaging (MRI) findings were evaluated before and during alendronate treatment. After treatment, not only the corrected serum calcium levels but also AFP levels and bone pain decreased; in addition, the regression of the metastatic focus was noted in the MRI analysis. These tumor inhibitory effects of alendronate have not been reported in HCC before; and alendronate might serve to prevent bone metastases in patients with HCC. In conclusion, two patients who developed hypercalcemia associated with bone metastasis after surgery for HCC were treated with alendronate and they experienced alleviation of the pain due to bone metastasis, improvement of their quality of life and a marked decrease in AFP levels with tumor regression.

Transport properties of a system y+L neutral and basic amino acid transporter. Insights into the mechanisms of substrate recognition

The properties of system y(+)L-mediated transport were investigated on rat system y(+)L transporter, ry(+)LAT1, coexpressed with the heavy chain of cell surface antigen 4F2 in Xenopus oocytes. ry(+)LAT1-mediated transport of basic amino acids was Na(+)-independent, whereas that of neutral amino acids, although not completely, was dependent on Na(+), as is typical of system y(+)L-mediated transport. In the absence of Na(+), lowering of pH increased leucine transport, without affecting lysine transport. Therefore, it is proposed that H(+), besides Na(+) and Li(+), is capable of supporting neutral amino acid transport. Na(+) and H(+) augmented leucine transport by decreasing the apparent K(m) values, without affecting the V(max) values. We demonstrate that although ry(+)LAT1-mediated transport of [(14)C]l-leucine was accompanied by the cotransport of (22)Na(+), that of [(14)C]l-lysine was not. The Na(+) to leucine coupling ratio was determined to be 1:1 in the presence of high concentrations of Na(+). ry(+)LAT1-mediated leucine transport, but not lysine transport, induced intracellular acidification in Chinese hamster ovary cells coexpressing ry(+)LAT1 and 4F2 heavy chain in the absence of Na(+), but not in the presence of physiological concentrations of Na(+), indicating that cotransport of H(+) with leucine occurred in the absence of Na(+). Therefore, for the substrate recognition by ry(+)LAT1, the positive charge on basic amino acid side chains or that conferred by inorganic monovalent cations such as Na(+) and H(+), which are cotransported with neutral amino acids, is presumed to be required. We further demonstrate that ry(+)LAT1, due to its peculiar cation dependence, mediates a heteroexchange, wherein the influx of substrate amino acids is accompanied by the efflux of basic amino acids.

Morphologic changes in forearm flaps of the oral cavity

PURPOSE

This study was undertaken to investigate the morphologic changes in the forearm flap in the oral environment.

PATIENTS AND METHODS

Histologic evaluation of biopsy specimens from 20 forearm flaps was done 1 to 75 months after intraoral reconstruction after treatment of cancer. Hematoxylin and eosin and Azan were used to stain the deparaffinized sections.

RESULTS

The clinical features of the grafted flap seemed to depend on the time since the operation. The cornified layer of the epidermis of the flaps showed thinning histologically.

CONCLUSION

After 11 months of exposure to an intraoral environment, "mucosalization" of the forearm flap is evident.

p-aminohippuric acid transport at renal apical membrane mediated by human inorganic phosphate transporter NPT1

Organic anions are secreted into urine via organic anion transporters across the renal basolateral and apical membranes. However, no apical membrane transporter for organic anions such as p-aminohippuric acid (PAH) has yet been identified. In the present study, we showed that human NPT1, which is present in renal apical membrane, mediates the transport of PAH. The K(m) value for PAH uptake was 2.66 mM and the uptake was chloride ion sensitive. These results are compatible with those reported for the classical organic anion transport system at the renal apical membrane. PAH transport was inhibited by various anionic compounds. Human NPT1 also accepted uric acid, benzylpenicillin, faropenem, and estradiol-17beta-glucuronide as substrates. Considering its chloride ion sensitivity, Npt1 is expected to function for secretion of PAH from renal proximal tubular cells. This is the first molecular demonstration of an organic anion transport function for PAH at the renal apical membrane.

Close correlation between estrogen treatment and renal phosphate reabsorption capacity

To determine the influence of estrogen on the activity of renal proximal tubular reabsorption of inorganic phosphate (Pi) in women, we examined the changes of the renal threshold phosphate concentration (also denoted as TmP/GFR), as well as the changes in the concentrations of mineral components in the circulation in two groups of women--one receiving hormone replacement therapy (HRT) and one receiving gonadotropin-releasing hormone agonists (GnRH-a) therapy. We also examined the changes in the concentrations of serum PTH in the GnRH-a group. The patients in the HRT group were continuously treated with 0.625 mg conjugated equine estrogens plus 2.5 mg medroxyprogesterone acetate per day. The patients in the GnRH-a group were treated with a monthly injection of 3.75 mg leuprolide acetate depot for 6 months. The values of TmP/GFR decreased in all of the patients who received HRT. The mean percentage change in TmP/GFR was -14.5% (range, -24.3% to -9.6%). In contrast, in all of the patients treated with GnRH-a, the values of TmP/GFR increased after 6 months of treatment (the mean percentage change was 28.5%; range, 18.2-78.3%) and returned to the preadministration level at 12 weeks after stopping therapy. In these patients, both the values of TmP/GFR and the concentrations of serum Pi correlated significantly with circulating estradiol levels (r = -0.767, P < 0.01 and r = -0.797, P < 0.01, respectively), but the concentrations of serum corrected calcium did not correlate. Moreover, in the same patients, the levels of serum intact PTH decreased significantly (P < 0.05) after 6 months of treatment, but at 12 weeks after stopping therapy the trends of these levels varied among individual patients. These results suggest that estrogen could act directly to suppress sodium-dependent Pi reabsorption in the renal proximal tubules.

Faropenem transport across the renal epithelial luminal membrane via inorganic phosphate transporter Npt1

We previously showed that the mouse inorganic phosphate transporter Npt1 operates in the hepatic sinusoidal membrane transport of anionic drugs such as benzylpenicillin and mevalonic acid. In the present study, the mechanism of renal secretion of penem antibiotics was examined by using a Xenopus oocyte expression system. Faropenem (an oral penem antibiotic) was transported via Npt1 with a Michaelis-Menten constant of 0.77 +/- 0.34 mM in a sodium-independent but chloride ion-sensitive manner. When the concentration of chloride ions was increased, the transport activity of faropenem by Npt1 was decreased. Since the concentration gradient of chloride ions is in the lumen-to-intracellular direction, faropenem is expected to be transported from inside proximal tubular cells to the lumen. So, we tested the release of faropenem from Xenopus oocytes. The rate of efflux of faropenem from Npt1-expressing oocytes was about 9.5 times faster than that from control water-injected Xenopus oocytes. Faropenem transport by Npt1 was significantly inhibited by beta-lactam antibiotics such as benzylpenicillin, ampicillin, cephalexin, and cefazolin to 24.9, 40. 5, 54.4, and 26.2% of that for the control, respectively. Zwitterionic beta-lactam antibiotics showed lesser inhibitory effects on faropenem uptake than anionic derivatives, indicating that Npt1 preferentially transports anionic compounds. Other anionic compounds, such as indomethacin and furosemide, and the anion transport inhibitor 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid significantly inhibited faropenem uptake mediated by Npt1. In conclusion, our results suggest that Npt1 participates in the renal secretion of penem antibiotics.

Regulation of intestinal Na+-dependent phosphate co-transporters by a low-phosphate diet and 1,25-dihydroxyvitamin D3

In a study of the rat intestinal P(i) transport system, an activator protein for rat Na/P(i) co-transport system (PiUS) was isolated and characterized. We also investigated the effects of restriction of vitamin D and P(i) (two of the most important physiological and pathophysiological regulators of P(i) absorption in the small intestine) on intestinal P(i) transport activity and the expression of Na/P(i) co-transporters that are expressed in rat small intestine. Rat PiUS encodes a 424-residue protein with a calculated molecular mass of 51463 Da. The microinjection of rat PiUS into Xenopus oocytes markedly stimulated Na(+)-dependent P(i) co-transport activity. In rats fed with a low-P(i) diet, Na(+)-dependent P(i) co-transport activity was increased approx. 2-fold compared with that of rats fed a normal P(i) diet. Kinetic studies demonstrated that this increased activity was due to an elevation of V(max) but not K(m). The PiUS mRNA levels showed an approximate doubling in the rats fed with the low-P(i) diet compared with those fed with the normal P(i) diet. In addition, after the administration of 1, 25-dihydroxyvitamin D(3) [1,25-(OH)(2)D(3)] to vitamin D-deficient animals, the P(i) uptake was significantly increased in the Na(+)-dependent component in the brush border membrane vesicle (BBMV) at 24 and 48 h. In addition, we found a further high-affinity Na/P(i) co-transport system in the BBMV isolated from the vitamin D-replete animals. The levels of type III Na/P(i) co-transporter PiT-2 mRNA were increased 24 and 48 h after 1,25-(OH)(2)D(3) administration to vitamin D-deficient animals, whereas PiUS and the type IIb Na/P(i) co-transporter mRNA levels were unchanged. In conclusion, we first cloned a rat activator protein, PiUS, and then studied its role along with that of other type III Na/P(i) co-transporters. PiUS and PiT-2 might be important components in the regulation of the intestinal P(i) transport system by P(i) restriction and 1,25-(OH)(2)D(3).

Identification of an amino acid transporter associated with the cystinuria-related type II membrane glycoprotein

We identified an amino acid transporter that is associated with the cystinuria-related type II membrane glycoprotein, rBAT (related to b(0,+) amino acid transporter). The transporter designated BAT1 (b(0, +)-type amino acid transporter 1) from rat kidney was found to be structurally related to recently identified amino acid transporters for system L, system y(+)L, and system x(-)C, which are linked, via a disulfide bond, to the other type II membrane glycoprotein, 4F2hc (4F2 heavy chain). In the nonreducing condition, a 125-kDa band, which seems to correspond to the heterodimeric complex of BAT1 and rBAT, was detected in rat kidney with anti-BAT1 antibody. The band was shifted to 41 kDa in the reducing condition, confirming that BAT1 and rBAT are linked via a disulfide bond. The BAT1 and rBAT proteins were shown to be colocalized in the apical membrane of the renal proximal tubules where massive cystine transport had been proposed. When expressed in COS-7 cells with rBAT, but not with 4F2hc, BAT1 exhibited a Na(+)-independent transport of cystine as well as basic and neutral amino acids with the properties of system b(0,+). The results from the present investigation were used to establish a family of amino acid transporters associated with type II membrane glycoproteins.

Daily pattern of energy metabolism in cirrhosis

The daily pattern of energy expenditure and the oxidation rates of carbohydrates, fats, and protein were evaluated by indirect calorimetry in 18 control subjects (Group 1) and 34 cirrhotic patients who were divided into Groups 2a and 2b showing indocyanin green retention rates at 15 min of <30% and 30% or more, respectively. The ratio of resting energy expenditure to basal energy expenditure (%REE) was higher in the cirrhotic patients than in the controls at 8:30 AM and 2:30 PM. The oxidation rates of carbohydrates and fats under fasting conditions in Group 2b patients were respectively lower, and higher than in Group 1 and 2a patients. After the subjects ate, glucose became the substrate preferentially metabolized, and the proportion of fat metabolized was reduced from 82.9+/-5.1% to 43.9+/-21.9% and from 70.7+/-14.1% to 46.8+/-13.9% in the patients with advanced and less advanced cirrhosis, respectively, and from 59.4+/-27.2% to 48.4+/-18.5% in the controls. The fasting concentrations of non-esterified fatty acids in Group 2b were also significantly higher than those in the Group 1 and Group 2a patients. After eating, these concentrations fell and reached similar levels in the patients and controls. These data indicated that the patients with cirrhosis developed the catabolic state of starvation in the morning because of a lack of glycogen stores. Therefore, frequent meal supplementation to prevent early-onset starvation and energy deficiency may be advisable in such patients to maintain a well-nourished condition.

[Regulation of gene expression and vitamin]

Action of 1,25-dihydroxyvitamin D, the most active metabolite of vitamin D, is exerted by the nuclear vitamin D receptor (VDR) mediated gene expression. Toward the expression of vitamin D function, several steps including 1,25-dihydroxyvitamin D production, tissue specific expression of VDR and transcription of target gene by VDR are involved. One of the important progress in vitamin D metabolism is the cloning of 25-hydroxyvitamin D-24-hydroxylase gene and 1 alpha-hydroxylase gene. Structural organization of the human VDR chromosomal gene and its promoter was also important to understand the amount of VDR expressed in tissues. A part of mechanism of tissue specific expression of VDR have recently been reported. Furthermore, VDR recruit several coactivators to achieve vitamin D-induced transactivation. Selective coactivator interaction with VDR may specify the array of biological actions of vitamin D.

Identification of Regulatory Sequences and Binding Proteins in the Type II Sodium/Phosphate Cotransporter NPT2 Gene Responsive to Dietary Phosphate

Dietary phosphate (P(i)) is a most important regulator for renal P(i) reabsorption. The type II sodium-dependent phosphate (Na/P(i)) cotransporters (NPT2) are located at the apical membranes of renal proximal tubular cells and major functional transporters associated with renal P(i) reabsorption. The consumption of a low-P(i) diet induces the synthesis of NPT2, whereas a high P(i) diet decreases it. The molecular mechanisms of regulation by dietary P(i) are not yet known. In this report, in weaning mice fed a low-P(i) diet for 4 days, the NPT2 mRNA level was increased 1.8-fold compared with mice fed a normal P(i) diet. This increase was due to an elevation of the transcriptional activity. In the NPT2 gene promoter, the DNA footprint analysis showed that six regions were masked by the binding protein, but at the position -1010 to -985 upstream of the transcription start site, the binding clearly responded to the levels of dietary P(i). The phosphate response element (PRE) of the NPT2 gene was found to consist of the motif related to the E box, 5'-CACGTG-3'. A yeast one-hybrid system was used to clone a transcription factor that binds to the PRE sequences in the proximal promoter of the NPT2 gene. Two cDNA clones that encoded protein of the mouse transcription factor muE3 (TFE3) were isolated. This is a DNA-binding protein that activates transcription through the muE3 site of the immunoglobulin heavy chain enhancer. TFE3 antibody completely inhibited the binding to the PRE. The coexpression of TFE3 in COS-7 cells transfected with the NPT2 gene promoter markedly stimulated the transcriptional activity. The feeding of a low P(i) diet significantly increased the amount of TFE3 mRNA in the kidney. These findings suggest that TFE3 may participate in the transcriptional regulation of the NPT2 gene by dietary P(i).

Physicochemical characteristics and toxicity of nickel oxide particles calcined at different temperatures

The physicochemical characteristics and cytotoxicity of two types of commercial nickel oxide particles (black and green nickel oxide) and five types of nickel oxide particles prepared by calcination of the black nickel oxide at 600-1000 degrees C were studied. Thermal analysis with mass spectroscopy showed that the black nickel oxide particles contained approximately 1.4% impurity, which seemed to be basic nickel carbonate. The calcination treatment at 600 degrees C increased the nickel content and decreased the oxygen content, but these remained constant in the particles treated at higher temperatures (700-1000 degrees C) and in the green nickel oxide particles. The water solubility of black nickel oxide particles was markedly greater than that of the other particles, especially in the first 24 h after mixing with water. The solubility of the calcined particles decreased with increasing calcination temperature. The cytotoxicity of these particles was evaluated by the viability of rat alveolar macrophages and by the inhibition of cell proliferation in Chinese hamster ovary cells. The black nickel oxide was the most cytotoxic of the particles examined, and this may be attributable, at least in part, to a rapid dissolution of nickel from the contained impurity. The toxicity of the calcined particles decreased with increasing calcination temperature. These results indicate that water solubility, which depends on calcination temperature, modulates the acute cytotoxicity of nickel oxide particles.

Antiviral activity of enterocin CRL35 against herpesviruses

Enterocin CRL35 is an antibacterial polypeptide of 3.5 x 10(3) Da produced by Enterococcus faecium CRL35. A series of experiments are described that show the enterocin also had antiviral activity against thymidine-kinase positive (tk+) and deficient (tk-) strains of herpes simplex (HSV) type 1 and 2 in Vero and BHK-21 cells. This activity was observed at 100 microg/ml, 15-fold lower than the cytotoxic concentration. In both cell lines there was a 2 log inhibition of infectivity. The compound inhibited viral multiplication in a dose-dependent manner and had no virucidal effect. Enterocin CRL35 also inhibited the virion-associated host shutoff in infected Vero cells showing that intracellular viral multiplication was affected.

Identification and functional characterization of a Na+-independent neutral amino acid transporter with broad substrate selectivity

We have isolated a cDNA from rat small intestine that encodes a novel Na+-independent neutral amino acid transporter with distinctive characteristics in substrate selectivity and transport property. The encoded protein, designated L-type amino acid transporter-2 (LAT-2), shows amino acid sequence similarity to the system L Na+-independent neutral amino acid transporter LAT-1 (Kanai, Y., Segawa, H., Miyamoto, K., Uchino, H., Takeda, E., and Endou, H. (1998) J. Biol. Chem. 273, 23629-23632) (50% identity) and the system y+L transporters y+LAT-1 (47%) and KIAA0245/y+LAT-2 (45%) (Torrents, D., Estevez, R., Pineda, M., Fernandez, E., Lloberas, J., Shi, Y.-B., Zorzano, A., and Palacin, M. (1998) J. Biol. Chem. 273, 32437-32445). LAT-2 is a nonglycosylated membrane protein. It requires 4F2 heavy chain, a type II membrane glycoprotein, for its functional expression in Xenopus oocytes. LAT-2-mediated transport is not dependent on Na+ or Cl- and is inhibited by a system L-specific inhibitor, 2-aminobicyclo-(2,2,1)-heptane-2-carboxylic acid (BCH), indicating that LAT-2 is a second isoform of the system L transporter. Compared with LAT-1, which prefers large neutral amino acids with branched or aromatic side chains, LAT-2 exhibits remarkably broad substrate selectivity. It transports all of the L-isomers of neutral alpha-amino acids. LAT-2 exhibits higher affinity (Km = 30-50 microM) to Tyr, Phe, Trp, Thr, Asn, Ile, Cys, Ser, Leu, Val, and Gln and relatively lower affinity (Km = 180-300 microM) to His, Ala, Met, and Gly. In addition, LAT-2 mediates facilitated diffusion of substrate amino acids, as distinct from LAT-1, which mediates amino acid exchange. LAT-2-mediated transport is increased by lowering the pH level, with peak activity at pH 6.25, because of the decrease in the Km value without changing the Vmax value. Because of these functional properties and a high level of expression of LAT-2 in the small intestine, kidney, placenta, and brain, it is suggested that the heterodimeric complex of LAT-2 and 4F2 heavy chain is involved in the trans-cellular transport of neutral amino acids in epithelia and blood-tissue barriers.

[The structural polymorphism in D8S580-STR region]

The STR structure of the D8S580 locus was analyzed by the base sequencing technique. Alleles were collected separately by urea denaturing polyacrylamide gel electrophoresis of the PCR amplification product, followed by cutting of the target DNA band from the gel, and reamplification. As a result, this locus was shown to have a complex STR structure consisting of four types of repeat units, i.e. GGAA (II), GAAA (III), GAAAA (IV), and GCAA (V). Of 53 unrelated Japanese individuals, 51 were heterozygous, and the most frequent allele was type IV 8-II 7 III 6 III 3 (16%). Forty-four alleles with distinct structures appeared once the samples tested. As 57 different alleles were detected in this study, this region is considered to be one of the locus that have a high degree of repetitive structural polymorphism and therefore useful in forensic science.

Nicotinamide inhibits sodium-dependent phosphate cotransport activity in rat small intestine

BACKGROUND

We recently reported that the administration of niceritorol (a nicotinic acid derivative which improves lipid metabolism and peripheral circulation, and is used for the treatment of hyperlipidaemia and impaired peripheral circulation) to patients with hyperphosphataemia undergoing dialysis decreased the serum phosphate (Pi) concentration. We found that this was due to an acceleration of faecal Pi excretion by niceritrol.

METHODS

Intestinal brush border membrane vesicles (BBMVs) were prepared from rat jejunum, and the Na+-dependent and Na+-independent Pi transport activities in these vesicles were measured. In addition, the functional Pi transporter from rat small intestine was injected in Xenopus oocytes, and the effect of nicotinamide on the levels of its expression were measured by northern blotting.

RESULTS

The Na+-dependent component was significantly decreased in the BBMVs isolated from rats treated with nicotinamide, while the Na+-independent component was not changed. Kinetic studies demonstrated that the decreased activity was due to reduction of the Vmax value and not an elevation of the Km values. When poly(A)+RNA from rats treated with nicotinamide was microinjected into Xenopus oocytes, the Pi transport activity was significantly decreased compared with that in the control animals. In addition, there were no significant changes in Na/Pi cotransporters and activators, but the vitamin D receptor mRNA level was reduced to 80% of the control level.

CONCLUSIONS

These observations suggest that nicotinamide may regulate the expression of a major functional Na/Pi cotransporter in the rat small intestine.

Sodium-dependent phosphate co-transporters

The renal proximal tubular reabsorption of inorganic phosphate (Pi) mediated by sodium-dependent phosphate (Na+/Pi) co-transporters plays a critical role in the maintenance of Pi homeostasis. Two nonhomologous Na+/Pi co-transporters (type I and type II) have been identified in the renal cortex of various species. The role of the type I co-transporter in Pi regulation remains to be clarified. Type II co-transporters play a major role in the regulation of renal Pi reabsorption by dietary Pi and parathyroid hormone, which regulate the rapid endocytosis/exocytosis of the transporters. Type III Na+/Pi co-transporters, which are expressed in a wide variety of tissues and are regulated by changes in the Pi concentration, have recently been described. The presence of a novel Pi-regulating hormone called 'phosphatonin' has been postulated in studies of the mechanisms of X-linked hypophosphatemic rickets and oncogenic osteomalacia. The regulation of phosphatonin and Na+/Pi co-transporters may provide novel pharmacological approaches to the treatment of these diseases.

Regulation of PiT-1, a sodium-dependent phosphate co-transporter in rat parathyroid glands

A cDNA encoding an Na+-Pi co-transporter, termed rat PiT-1, has now been isolated from rat parathyroid. Expression of rat PiT-1 in Xenopus oocytes revealed that it possesses Na+-dependent Pi co-transport activity. The amount of PiT-1 mRNA in the parathyroid of vitamin D-deficient rats was reduced compared with that in normal animals, and increased markedly after administration of 1,25-dihydroxyvitamin D3. Furthermore, the abundance of PiT-1 mRNA in the parathyroid was much greater in rats fed a low-Pi diet than in those fed a high-Pi diet. Thus, rat PiT-1 may contribute to the effects of Pi and vitamin D on parathyroid function.

The caudal-related homeodomain protein Cdx-2 regulates vitamin D receptor gene expression in the small intestine

The actions of 1,25-dihydroxyvitamin D3 (1,25(OH)2 D3) are mediated through the nuclear vitamin D receptor (VDR). The regulation of VDR abundance plays an important role in determining the magnitude of the target cell response to 1,25(OH)2D3. The major physiological activity of 1,25(OH)2D3 is the regulation of calcium absorption in the small intestine, and the level of VDR is an important factor in this regulation. However, the characterization of VDR gene expression in the small intestine remains unknown. In the present study, we investigated the regulation of the human VDR (hVDR) gene expression in the small intestine. The 4.0 kb of the 5'-flanking region of the hVDR gene promoter was cloned and characterized by the measurement of luciferase activity and an electrophoretic mobility-shift assay (EMSA). With the EMSA, we found that Cdx-2 (a homeodomain protein-related caudal) binds to the sequence 5'-ATAAAAACTTAT-3' at -3731 to -3720 bp (hVD-SIF1) relative to the transcription start site of the hVDR promoter. This sequence is very similar to the human sucrase-isomaltase footprint 1 (SIF1) element. With a competition analysis and specific antibodies for Cdx-2, we demonstrated that Cdx-2 is able to activate VDR gene transcription by binding to this element. The mutation of the hVD-SIF1 sequence in the hVDR gene promoter markedly suppressed the transactivation of the reporter gene in Caco-2 cells. In addition, the DNA fragment (-3996 to -3286) containing the hVD-SIF1 binding site increased transcription when placed upstream of the herpes simplex virus thymidine kinase promoter. These findings suggest that Cdx-2 plays an important role in the intestine-specific transcription of the hVDR gene.

Cellular and molecular mechanisms of dietary regulation on rat intestinal H+/Peptide transporter PepT1

BACKGROUND & AIMS

Dietary regulation is one of the most important factors of intestinal peptide transport. However, the cellular and molecular mechanisms of dietary regulation of the intestinal peptide transport system remain unknown. This study investigated the molecular mechanism of transcriptional activation of intestinal peptide transporter (PepT1) gene by the dietary protein. The promoter region of the rat PepT1 gene was isolated and characterized.

METHODS

PepT1 messenger RNA levels were determined by Northern blot analysis. In transient transfection experiments, effects of amino acid and dipeptide on luciferase activity were investigated.

RESULTS

The proximal promoter region of the rat PepT1 gene has a TATA-like box and a GC box sequence. The luciferase activities of the clone -351 RPT-LUC responded to particular amino acids (phenylalanine, arginine, and lysine) and dipeptides (Gly-Sar, Gly-Phe, Lys-Phe, and Asp-Lys). An AP-1 binding site and an amino acid-responsible element were present at -295 and -277 nucleotides relative to the transcription start site in this region.

CONCLUSIONS

These results suggest that the up-regulation of dipeptide transport activity by dietary protein is caused by transcriptional activation of the PepT1 gene by selective amino acids and dipeptides in the diet.

Mutational analyses in four Japanese families with X-linked liver phosphorylase kinase deficiency type 1

We analysed the gene of the human alpha-subunit of liver phosphorylase kinase (PHKA2) in four Japanese families with X-linked liver phosphorylase kinase deficiency type 1 by RT-PCR followed by PCR-single-strand conformation polymorphism and direct DNA sequencing. In this study, two novel mutations (Y116D and 2675A-->G) and one mutation previously reported (P1205L) were identified, revealing molecular heterogeneity in Japanese patients. Considering the dissimilarity in phenotype among our patients even with an identical mutation in the PHKA2 gene, it seems that each genetic deficiency in this gene may not be the only factor to determine the clinical heterogeneity in this disease.

Identification of three isoforms for the Na+-dependent phosphate cotransporter (NaPi-2) in rat kidney

We have isolated three unique NaPi-2-related protein cDNAs (NaPi-2alpha, NaPi-2beta, and NaPi-2gamma) from a rat kidney library. NaPi-2alpha cDNA encodes 337 amino acids which have high homology to the N-terminal half of NaPi-2 containing 3 transmembrane domains. NaPi-2beta encodes 327 amino acids which are identical to the N-terminal region of NaPi-2 containing 4 transmembrane domains, whereas the 146 amino acids in the C-terminal region are completely different. In contrast, NaPi-2gamma encodes 268 amino acids which are identical to the C-terminal half of NaPi-2. An analysis of phage and cosmid clones indicated that the three related proteins were produced by alternative splicing in the NaPi-2 gene. In a rabbit reticulocyte lysate system, NaPi-2 alpha, beta, and gamma were found to be 36, 36, and 29 kDa amino acid polypeptides, respectively. NaPi-2alpha and NaPi-2gamma were glycosylated and revealed to be 45- and 35-kDa proteins, respectively. In isolated brush-border membrane vesicles, an N-terminal antibody was reacted with 45- and 40-kDa, and a C-terminal antibody was reacted with 37-kDa protein. The sizes of these proteins corresponded to those in glycosylated forms. A functional analysis demonstrated that NaPi-2gamma and -2alpha markedly inhibited NaPi-2 activity in Xenopus oocytes. The results suggest that these short isoforms may function as a dominant negative inhibitor of the full-length transporter.

Molecular cloning of a second human stanniocalcin homologue (STC2)

Stanniocalcin (STC) is a Ca- and phosphate-regulating hormone produced by the corpuscles of Stannius in bony fishes. The mammalian homologue of STC has recently been reported (STC1), which stimulates the phosphate uptake of kidney. Here we report the cloning of a second mammalian stanniocalcin (STC2) from the human osteosarcoma cDNA library. STC2 has 302 amino acid residues with 34% identity with STC1 and eel STC. STC2 has a conserved N-glycosylation site and is rich in cysteines as is the case with other stanniocalcins. STC2 has the same exon-intron boundaries as STC1. The culture medium of STC2-transfected CHO cells inhibited the promoter activity of Na-phosphate cotransporter (NaPi-3) and also inhibited the phosphate uptake of a kidney cell line (OK cells). Therefore, the function of STC2 seems to be opposite to that of STC1 on Na-phosphate cotransporter. Northern blot analysis revealed multiple transcripts in number of human tissues with high levels being present in skeletal muscle and heart. STC2 was also expressed in mice widely and its expression was lower in hypophosphatemic mice (Hyp mice) in many organs. We have cloned a widely expressed new human stanniocalcin homologue which suppressed the expression of renal Na-phosphate cotransporter.

Expression cloning and characterization of a transporter for large neutral amino acids activated by the heavy chain of 4F2 antigen (CD98)

A cDNA was isolated from rat C6 glioma cells by expression cloning which encodes a novel Na+-independent neutral amino acid transporter designated LAT1. For functional expression in Xenopus oocytes, LAT1 required the heavy chain of 4F2 cell surface antigen (CD98), a type II membrane glycoprotein. When co-expressed with 4F2 heavy chain, LAT1 transported neutral amino acids with branched or aromatic side chains and did not accept basic amino acids or acidic amino acids. The transport via LAT1 was Na+-independent and sensitive to a system L-specific inhibitor 2-aminobicyclo-(2,2,1)-heptane-2-carboxylic acid. These functional properties correspond to those of the classically characterized amino acid transport system L, a major nutrient transporter. In in vitro translation, LAT1 was shown to be a nonglycosylated membrane protein consistent with the property of 4F2 light chain, suggesting LAT1 is at least one of the proteins formerly referred to as 4F2 light chain. LAT1 exhibits relatively low but significant amino acid sequence similarity to mammalian cationic amino acid transporters and amino acid permeases of bacteria and yeasts, indicating LAT1 is a new member of the APC superfamily. Because of highly regulated nature and high level of expression in tumor cell lines, LAT1 is thought to be up-regulated to support the high protein synthesis for cell growth and cell activation. The cloning of LAT1 is expected to facilitate the research on the protein-protein interaction in the transporter field and to provide a clue to the search for still unidentified transporters.

Hepatic sinusoidal membrane transport of anionic drugs mediated by anion transporter Npt1

The purpose of our study was to establish the localization of the anion transporter Npt1 in liver and the relevance of Npt1 to carrier-mediated hepatic transport of beta-lactam antibiotics. Immunocytochemical examination of mouse liver with antiserum for Npt1 showed basolateral (sinusoidal) membrane localization. Function of Npt1 was characterized in Xenopus laevis oocytes. Injection of in vitro-transcribed cRNA into oocytes resulted in an increased uptake of [14C]benzylpenicillin (PCG). The Npt1-mediated uptake was saturable with a Michaelis constant (Km) of 0.46 +/- 0.18 mM and a maximum rate (Vmax) of 46.6 +/- 8.5 pmol/60 min/oocyte, and the uptake of [14C]PCG was independent of Na+ and pH, but dependent on chloride ion. Npt1-mediated [14C]PCG uptake was inhibited by several beta-lactam antibiotics and probenecid. Oocytes injected with Npt1-cRNA demonstrated significantly enhanced transport activity for other anionic compounds such as [14C]faropenem, [14C]foscarnet and [3H]mevalonic acid, as well as [14C]PCG, compared with water-injected oocytes. In conclusion, Npt1 is suggested to participate in hepatic sinusoidal membrane transport of organic anions such as beta-lactam antibiotics as well as inorganic anions for the efflux from hepatocyte-to-blood direction.

Rapid and convenient method of autoradiography for DNA cloning using digital imaging analysis

Digital image analysis has been used for various biochemical and molecular biological analyses instead of autoradiography with X-ray film. However, in such cases the data manipulated by an imaging analyzer was generally printed out on normal printing paper. With normal paper, it is difficult to align the signal or its position relative to the original sample. Here in, we demonstrate it to be convenient and accurate to align signal obtained by imaging analyzer with OHP film.

Effects of dietary Pi on the renal Na+-dependent Pi transporter NaPi-2 in thyroparathyroidectomized rats

Dietary Pi and parathyroid hormone (PTH) are two most important physiological and pathophysiological regulators of Pi re-absorption in the renal proximal tubule. Effects of dietary Pi on Na+/Pi co-transporter NaPi-2 were investigated in thyroparathyroidectomized (TPTX) rats. NaPi-2 protein and mRNA in the kidney cortex of TPTX rats were increased approximately 3.8- and 2.4-fold in amount respectively compared with those in the sham-operated animals. Administration of PTH to the TPTX rats resulted in a decrease in the amount of NaPi-2 protein, but not in the abundance of NaPi-2 mRNA. Deprivation of dietary Pi in the TPTX rats did not affect the amount of NaPi-2 mRNA and protein. In the Pi-deprived TPTX rats, feeding of a high-Pi diet resulted in marked decreases in Pi transport activity and the amount of NaPi-2 protein in the superficial nephrons. Immunohistochemical analysis demonstrated that administration of PTH to TPTX rats resulted in a decrease in NaPi-2 immunoreactivity from both superficial and juxtamedullary nephrons within 4 h. Switching TPTX animals from a low-Pi diet to the high-Pi diet decreased NaPi-2 immunoreactivity from superficial nephrons, but not from juxtamedullary nephrons, within 4 h. These results suggest that dietary Pi could regulate the amount of NaPi-2 protein in the superficial nephrons in a PTH-independent manner.