Postnatal development of the harderian gland in the rabbit: light and electron microscopic observations

We have investigated the development of the Harderian glands of Japanese white rabbits from birth to 4 months of age. Although two types of secretory cells comprise the glandular epithelium of the pink and white lobes in fully developed glands, the time of neonatal appearance is different between the two. Cells consisting of the pink lobe first appear on the third day of life, while cells of the white appear around seventh day of life. The ultrastructure of the Harderian glands from 1-week-old rabbits resembles that of adult animals. The gland can be divided into three parts on the basis of their epithelial cell composition at the electron microscopic level. The respective parts are composed of: (1) one type of cells with large vacuoles (pink lobe), (2) one type of cells with small vacuoles (white lobe), and (3) two types of cells with large and small vacuoles (pink-white mixed portion). The relative number of plasma cells per 1 mm2 is low in both pink and white lobes during early postnatal life. However, in adult animals, the white lobe has a larger number of plasma cells than the pink lobe. These results suggest the possibility that the white lobe participates in the immune system more than does the pink.

Enhancement of apoptosis in developing chick neural retina cells by basic fibroblast growth factor

To evaluate the role of various growth factors in naturally occurring cell death during development of the neural retina, we examined the effects of such factors on the nuclear morphology and the size of DNA in cultured chick embryonic neural retina cells. Basic fibroblast growth factor (bFGF) increased internucleosomal cleavage of DNA and nuclear fragmentation in a time- and dose-dependent manner. The effect was inhibited by anti-bFGF antibody, suramin, and cycloheximide. Epidermal growth factor, platelet-derived growth factor, nerve growth factor, tumor necrosis factor-alpha, and dexamethasone had no effect. These results provide evidence that bFGF may eventually act as a lethal factor inducing apoptotic cell death during the development of the neural retina in chick embryo.

Novel homozygous and compound heterozygous mutations of sterol 27-hydroxylase gene (CYP27) cause cerebrotendinous xanthomatosis in three Japanese patients from two unrelated families

The autosomal recessively inherited cholesterol metabolic disease, cerebrotendinous xanthomatosis (CTX), is caused by mutations in the sterol 27-hydroxylase gene. Three Japanese CTX patients from two unrelated families were studied genetically. By DNA sequence analysis a novel mutation of A for G substitution at amino acid position 372 (CGG 372Arg to CAG 372Gln) was identified in one of the CTX families. The mutation was also found in two patients from the other family, with a compound heterozygous pattern of A for G substitution at amino acid position 441 (CGG 441Arg to CAG 441Gln). The latter mutation was the same as previously reported by our group (J. Lipid Res. 1994. 35: 1031-1039). As the two mutations changed the restriction enzyme sites, rapid screening methods were developed for the detection of the carriers. Transfection of the two mutant cDNAs into COS cells resulted in markedly reduced sterol 27-hydroxylase activity. These results indicate that the two mutations are responsible for the deficiency of the sterol 27-hydroxylase activity in these patients. The features of mutations identified till now in Japanese CTX patients are also reviewed.

Ornithine decarboxylase overexpression in mouse 10T1/2 fibroblasts: cellular transformation and invasion

BACKGROUND

Ornithine decarboxylase (ODC) plays a pivotal role in the synthesis of polyamines, a group of chemical compounds that are essential for cell growth. Recent reports have shown that ODC overexpression may be involved in malignant transformation of immortalized NIH 3T3 cells. We have demonstrated that ODC-overproducing mouse breast cancer cells are more invasive in vitro than control cells. However, little information is available concerning the relationship between ODC overexpression, tumor invasion, and metastasis and the signal transduction pathways involved in ODC-induced transformation and invasion.

PURPOSE

Our purpose was twofold: 1) to determine whether ODC overexpression is directly involved in tumor cell invasion and 2) to determine whether ODC overexpression induces mitogen-activated protein (MAP) kinase activities that are associated with cell growth and transformation.

METHODS

We transfected C3H clone 8 mouse 10T1/2 fibroblasts with an expression vector that carries a complementary DNA encoding rat ODC. Neomycin-resistant cells that overproduced ODC (4-6.5 times the control levels) were isolated. The transformed phenotype of these cells was determined by assessing colony formation and anchorage-independent growth in soft agar. The invasiveness of the cells was studied by means of an invasion assay that used Matrigel-coated filters in Boyden chambers. The MAP kinase activity of the cells was assayed by an in-gel kinase assay, using myelin basic protein as the substrate.

RESULTS

Overexpression of ODC induced not only cell transformation and anchorage-independent growth in soft agar but also invasiveness through a Matrigel-coated filter. The ODC-overproducing transfectants showed enhanced MAP kinase activity that paralleled the magnitude of cell invasiveness.

CONCLUSIONS

ODC plays a pivotal role not only in cell transformation but also in cancer cell invasion. ODC overexpression enhanced MAP kinase activity.

IMPLICATIONS

Our results demonstrate a connection between the polyamine/ODC and the MAP kinase signal transduction pathways and suggest that MAP kinase may play a pivotal role in ODC-induced cell transformation and invasion.

Novel regulation of delta-aminolevulinate synthase in the rat harderian gland

The mode of expression of delta-aminolevulinate synthase (ALAS), as well as that of mRNAs for other heme pathway enzymes, was examined in the rat Harderian gland. Northern blot and in situ hybridization analyses demonstrated that the non-specific ALAS (ALAS-N) mRNA is highly expressed in this tissue, whereas the erythroid-specific ALAS (ALAS-E) mRNA is not. Immunoblot analysis of ALAS also confirmed this finding at the protein level. ALAS-N mRNA was maximally induced in the Harderian gland and was not increased further by treatment of animals with 2-allyl-2-isopropylacetamide (AIA). The levels of mRNAs for other heme pathway enzymes, i.e., delta-aminolevulinate dehydratase, porphobilinogen deaminase, uroporphyrinogen decarboxylase, and coproporphyrinogen oxidase, also were increased markedly in the Harderian gland and not influenced by AIA treatment. The level of ferrochelatase (FeC) mRNA in the gland was, however, lower than that in the liver. The gland contained an extremely high level of protoporphyrin, while heme was undetectable. Microsomal heme oxygenase-1 (HO-1) mRNA levels were significantly higher in the Harderian gland than in the liver. When isolated glands were incubated with hemin in vitro in organ cultures, the level of HO-1 mRNA was increased, whereas the ALAS-N mRNA level was not. These findings indicate that markedly elevated levels of protoporphyrin and extremely low levels of heme in the Harderian gland are the results of both decreased expression of FeC and markedly increased expression of ALAS-N and HO-1. The constitutive expression of the ALAS-N gene in the Harderian gland suggests a novel transcriptional control mechanism of this gene.

Effect of the photoperiod in modulating the androgenic control of 1-alkyl-2,3-diacylglycerol composition in the harderian gland of the golden hamster, Mesocricetus auratus

The golden hamster Harderian gland produces a lipid secretion consisting mainly of 1-alkyl-2,3-diacylglycerol. We investigated the composition of alkyl and acyl groups in male and female hamster Harderian alkyldiacylglycerol, in animals kept in long and short photoperiods. Female hamsters in long days have alkyl groups with long saturated straight chains (C18:0 and C20:0) and methyl-branched chains (even and odd chain length iso-branched and odd chain length anteiso-branched chains). Acyl groups in females in long days are mostly long straight chains (C16:0) and methyl-branched chains. In females, short photoperiods led to reductions in the proportions of methyl-branched chains and changes in the proportions of straight chain alkyl and acyl groups; these changes were prevented by pinealectomy. Male hamsters with intact gonads, maintained in long days, had no methyl-branched chain alkyl or acyl groups; saturated straight chains were generally shorter than those of females and the odd chain length saturated C15:0 acyl group was common. Short photoperiods did not significantly alter the composition of male alkyldiacylglycerol. Castrated male hamsters in long days showed a distinctively female phenotype, with long straight chains and methyl-branched alkyl and acyl groups. Castrated males in short days showed a mixture of male and female characteristics: shorter straight chain alkyl and acyl groups, a total absence of methyl-branched alkyl groups, and the presence of methyl-branched acyl groups. These results and those of other studies suggest that testosterone controls the enzymes isovaleryl acyl-CoA dehydrogenase and 2-methyl branched-chain acyl-CoA dehydrogenase; in the absence of these enzymes, the primers for the synthesis of methyl-branched chain fatty acids are produced. Our results indicate that this control is modulated by short photoperiods (perhaps due to reduced prolactin levels). It is also suggested that characteristics of male-type alkyldiacylglycerol are better adapted to conditions of autumn and winter than are those of female-type alkyldiacylglycerol.

Anti-alpha3 integrin antibody induces the activated form of matrix metalloprotease-2 (MMP-2) with concomitant stimulation of invasion through matrigel by human rhabdomyosarcoma cells

Proteolytic enzymes, such as matrix metalloproteases (MMPs), play a pivotal role in cancer invasion and metastasis. Invasive human rhabdomyosarcoma cells (RD) secreted proMMP-2 (72-kDa progelatinase). We found that anti-alpha3 and -alpha2 integrin antibodies induced the activated form of MMP-2 and enhanced proMMP-2 secretion by RD cells. The effect of anti-alpha2 integrin antibody was less prominent than that seen with anti-alpha3 integrin antibody. Moreover, we have found that anti-alpha3 and -alpha2 integrin antibodies enhanced RD-cell invasion through matrigel (reconstituted basement membrane) by 2.6- and 2.0-fold respectively this process was abrogated by neutralizing antibody to MMP-2. These data suggest that signaling events induced by anti-alpha3 integrin antibody may be involved in RD-cell invasion as a result of modulation of matrix-metalloprotease expression.

Effects of monensin on tropoelastin metabolism in vascular smooth muscle cells: monensin causes intracellular degradation of accumulated tropoelastin

Treatment with 80 nM monensin for 48 h resulted in impairment of tropoelastin secretion during the initial 6 h and subsequent reduction of tropoelastin synthesis from 18 to 48 h to one-tenth. The steady state level of tropoelastin mRNA started to decrease at 6 h and reached one-fifth of the control level by 48 h. A pulse-chase experiment after 24 h monensin treatment demonstrated that half of the accumulated tropoelastin in the cells was rapidly degraded within 120 min. These results indicate that the marked reduction in tropoelastin synthesis from 6 to 48 h treatment may be caused by both a reduction in the tropoelastin mRNA level and accelerated intracellular degradation of tropoelastin. Thus, monensin modulates tropoelastin expression through pretranslational and posttranslational mechanisms.

Genetic analysis of a Japanese cerebrotendinous xanthomatosis family: identification of a novel mutation in the adrenodoxin binding region of the CYP 27 gene

Cerebrotendinous xanthomatosis (CTX), an autosomal recessive lipid-storage hereditary disorder, is caused by mutations in the sterol 27-hydroxylase gene (CYP 27). A 24-year-old female Japanese CTX patient and her parents were studied for a CYP 27 mutation. Multiple xanthomas were the main complaint of the patient and plasma cholestanol level was markedly elevated. Sterol analysis of a xanthoma biopsy confirmed cholesterol and cholestanol deposition, and the cholestanol accounted for 8.1% of the total sterols. Sterol 27-hydroxylase activity in fibroblasts derived from the patient was undetectable, while the activities in fibroblasts from her mother and father were 54% and 41% of the normal level, respectively. Direct sequence analysis showed a missense mutation of A for G substitution in the CYP 27 gene at codon 362 (CGT 362Arg to CAT 362His) with a homozygous pattern in the patient, and a heterozygous pattern in the parents. The mutation, which eliminates a normal HgaI endonuclease site at position 1195 of the cDNA and is located at the adrenodoxin binding region of the gene, is most probably responsible for the decreased sterol 27-hydroxylase activity in this Japanese CTX family. The combined data strongly support that the primary enzymatic defect in CTX is the disruption of sterol 27-hydroxylase and that the disease is inherited in an autosomal recessive trait.

Analysis of connective tissue macromolecular components in Ishibashi rat skin: role of collagen and elastin in cutaneous aging

The Ishibashi (IS) rat, established from cross-breeding between Wistar and wild rats, has a unique skin appearance, with wrinklings and furrows indicative of skin aging appearing at the age of 12 weeks. To understand the underlying mechanism of the formation of wrinkles, macromolecular components of connective tissue, collagen and elastin, in the young (5-6-week-old) and the aged (23-30-week-old) IS rat skins were biochemically analyzed. Hydroxyproline and isodesmosine contents in the aged IS rats were reduced 22% (P < 0.05) and 37% (P < 0.05) compared to the young rats, whereas no significant differences in the contents of both macromolecules in control Sprague-Dawley (SD) rats were seen. The relative content of type III collagen was unaltered between the young and aged skins of both IS and SD rats. A relative decrease in the intact elastin molecule (65 kDa) and a relative increase in the elastin fragments with lower molecular weights were observed in the aged IS rat skin by immunoblotting method. These results indicate that the reduction in collagen and elastin contents and increased degradation of elastin molecules in the aged IS rat skin could be related to the formation of wrinkles. Thus, the IS rat may provide a useful model for the study of skin aging.

PET analysis of a case of cerebrotendinous xanthomatosis presenting hemiparkinsonism

We describe a 34-year-old Japanese woman presenting gait difficulty and Achilles tendon swelling. The patient was diagnosed as having cerebrotendinous xanthomatosis (CTX) based on the high serum cholestanol level and diminished enzymatic activity of 27-hydroxylase of fibroblasts from her skin. Her clinical presentation was atypical regarding the presence of hemiparkinsonism and absence of apparent cataract, dementia, and cerebellar ataxia. Although MRI studies could not detect any abnormality in the basal ganglia or midbrain, PET analysis using [18F]-6-fluoro-L-dopa revealed reduced uptake of dopamine into the putamen, suggesting the impairment of presynaptic dopaminergic neurons.

Two distinct long-chain-acyl-CoA synthetases in guinea pig Harderian gland

Two distinct long-chain-acyl-CoA synthetases which have different kinetic properties were identified in the guinea pig Harderian gland. One was localized in the microsomes and the other in the mitochondria. The relative V(max) values of the microsomal enzyme were 8.1, 1.7 and 1 and the apparent Km values were 66.7, 12.0 and 30.0 microM for palmitic, linoleic and arachidonic acids, respectively. The relative V(max) values of the mitochondrial enzyme were 2.7, 3.5 and 1 and the apparent Km values were 33.3, 29.9 and 30.0 microM for palmitic, linoleic and arachidonic acids, respectively. The relative V(max) values for the liver microsomal enzyme were 2.0, 2.5 and 1, while those of the liver mitochondrial enzyme were 4.1, 3.9 and 1 with palmitic, linoleic and arachidonic acids, respectively. There were no difference between the microsomal and the mitochondrial enzymes in the liver, regarding apparent Km values; these were 38.4, 29.9 and 22.0 microM for palmitic, linoleic and arachidonic acids, respectively. Thus, the substrate specificity and catalytic rate of the mitochondrial enzyme in Harderian gland for palmitic, linoleic and arachidonic acids were similar to the liver enzyme, but not to the microsomal enzyme in Harderian gland. On the other hand, the antiserum raised against the rat liver enzyme immune-titrated and immuno-blotted the enzymes from Harderian gland microsomes and liver, but not so the enzyme from Harderian gland mitochondria. Thus, the microsomal enzyme in Harderian gland had a common immunogenic epitope(s) with the liver enzyme, but the mitochondrial enzyme did not. The Harderian gland mitochondrial enzyme was a distinct protein from liver enzymes. The catalytic and immunogenic characteristics suggest that the enzyme proteins in the Harderian gland are unique, that is, different from that in the liver. The large V(max) value of the Harderian gland microsomal enzyme for palmitic acid suggests that it contributes to the synthesis of a large amount of the secretory lipid and the high Km value to maintenance of cellular lipid in this organ. The evidence that long-chain-acyl-CoA synthetase in the mitochondria is distinct from that in the microsomes was first found in guinea pig Harderian gland.

Sexual diversity of the lipid metabolism in the Harderian gland of the golden hamster

Fatty acid and alkyl compositions of 1-alkyl-2,3-diacylglycerols (ADG) in the Harderian gland of the golden hamster were determined. Fatty acids of male ADG consisted of straight chain saturated acids ranging from C12 to C22. Both even- and odd-numbered acids were observed, indicating that acetyl- and propionyl-CoAs were equally used as primers in the fatty acid synthesis. In female ADG a large amount of iso- and anteiso-branched fatty acids were detected. Odd-numbered acids (C15, 17, 19, and 21) contained iso- together with anteiso-branchings, and even-numbered acids (C16 and 18) contained iso-branchings. These findings suggested that isobutyryl-, isovaleryl-, and 2-methylbutyryl-CoAs were used as primers in addition to acetyl- and propionyl-CoAs in fatty acid synthesis in the female gland. Such unusual primers are catabolic intermediates of valine, leucine, and isoleucine, respectively. Male ADG contained straight chain saturated alkyl residues ranging from C14 to 21. In the case of female ADG, though the main component was C18:O, most alkyl components had branchings at the iso- and anteiso-positions. NMR data suggested the presence of propionic acid at the C3 position of glycerol in the male ADG and of isovaleric and 2-methylbutyric acids at the same position in the female ADG. These results suggest that the sexual differences of the lipids in the Harderian gland of the golden hamster are determined at the step of fatty acid synthesis depending on the available precursors in the male and female glands. We speculate that sex hormones affect the metabolism of branched chain amino acids and bring about the dramatic diversities of the lipid compositions in the male and female glands.

Localization of porphyrin in mouse Harderian glands

Lipid secreting Harderian glands in the ocular region of rodents contain a large amount of metal-free porphyrins. The localization of these porphyrins and the areas of formation of the lipidporphyrin complexes in the glandular lumina have not been clearly defined. We therefore examined the intracellular localization of porphyrin fluorescence both in tissue sections and in cultured cells of Harderian glands of 5 weeks old female ICR mice, using confocal UV-laser scanning microscopes. The fluorescence appeared in glandular cells containing lipid droplets, but not in non-glandular cells (e.g. myoepithelial or interstitial) without these droplets. Fluorescence in the cells was recognized in the cytoplasm, but there was no evidence indicating that porphyrins were restrictively stored in mitochondria. Nuclei and lipid droplets lacked fluorescence. It is thus reasonable to conclude that porphyrins accumulate in the cytoplasm, and that porphyrins and lipids are secreted separately from glandular cells. The lipid-porphyrin complex is therefore probably formed in the glandular lumina and not within the glandular cells.

Androgenic control of 1-alkyl-2,3-diacylglycerol in the harderian gland of the golden hamster, Mesocricetus auratus

Harderian glands of golden hamsters produce a copious lipid secretion, most of which is in the form of 1-alkyl-2,3-diacylglycerol (ADG). Sexual differences are seen in the composition of golden hamster ADG and in the morphology of secretory lipid droplet. ADGs from females contained abundant iso- and anteiso-branched chain alkyl groups and fatty acids [Seyama, Y., Otsuka, H., Ohashi, K., Vivien-Roels, B., and Pevet, P. (1995) J. Biochem. 117, 661-670]. Female hamsters were either untreated or given subcutaneous testosterone pellets. Treatment of females with testosterone led to the disappearance of such branched chain alkyl groups and fatty acids. Intact males had ADGs with entirely saturated straight chain alkyl groups and fatty acids. Castration led to the appearance of iso- and anteiso-branched chain alkyl groups and fatty acids. These observations suggested that the production of branched chain fatty acids in the Harderian gland of golden hamster is inhibited by testosterone at the step of isovaleryl-CoA dehydrogenase and 2-methyl branched-chain acyl-CoA dehydrogenase

Isolation of three novel cholinergic neuron-specific gangliosides from bovine brain and their in vitro syntheses

In the present study, three extremely minor but novel Chol-1 antigens, termed X1, X2, and X3 have been isolated from bovine brain gangliosides. Based on the results of sialidase degradation, TLC-immunostaining with anti-Chol-1 antibody and fast atom bombardment mass spectrometry, their chemical structures were identified as: III6NeuAc-GgOse4Cer (X1: GM1 alpha) III6NeuAc,II3NeuAc-GgOse4Cer (X2: GD1a alpha) III6NeuAc,II3NeuAc-NeuGc-GgOse4Cer (X3: GT1b alpha) The yields of GM1 alpha, GD1a alpha, and GT1b alpha, were approximately 150, 20, and 10 micrograms, respectively, from 10 g of the bovine brain ganglioside mixture. In conjunction with our previous observations, all gangliosides with anti-Chol-1 reactivity were found to contain a common sialyl alpha 2-6 N-acetylgalactosamine residue, indicating that this unique sialyl linkage is the specific antigenic determinant. We subsequently examined the biosynthesis of the three novel Chol-1 gangliosides using rat liver Golgi fraction as an enzyme source. The results showed that GM1 alpha, GD1a alpha, and GT1b alpha were synthesized from asialo-GM1, GM1a, and GD1b, respectively, by the action of a GalNAc alpha 2-6sialyltransferase.

Endothelin-1 and vasopressin activate Ca(2+)-permeable non-selective cation channels in aortic smooth muscle cells: mechanism of receptor-mediated Ca2+ influx

The effects of vasopressin and endothelin-1 on cultured aortic smooth muscle cell lines (A7r5) were investigated by measurements of intracellular calcium [Ca2+]i and the patch-clamp techniques. Vasopressin and endothelin-1 (100 nM) evoked an initial peak followed by a smaller sustained rise of [Ca2+]i in the presence of extracellular calcium [Ca2+]o. In the absence of [Ca2+]o, only the initial peak of [Ca2+]i was observed. Therefore, the initial peak of [Ca2+]i was mainly due to calcium release from the storage sites, whereas the later sustained rise of [Ca2+]i was due to the calcium entry from outside. The sustained rise of [Ca2+]i was unaffected by nifedipine (10 microM) significantly, but was completely abolished by La3+ (1 mM). Under current clamp conditions with K(+)-internal solution, vasopressin and endothelin-1 (100 nM) produced hyperpolarization, then followed by depolarization. Under voltage clamp conditions at a holding potential of -40 mV, both vasopressin and endothelin-1 first activated the outward current, then followed by a long-lasting inward current with a high noise level. The first outward current was abolished by charybdotoxin (100 nM), Cs+ in the patch pipette and high EGTA (10 mM) in the pipette, suggesting that it was a Ca(2+)-sensitive K+ current (IK.Ca). The inward current was still elicited with the patch pipette containing Cs(+)-internal solution, and reversed at about 0 mV. The reversal potential was not significantly altered by the replacement of [Cl-]i or [Cl-]o, proposing that the inward current is a cation selective channel (IN.S.). The inward current was also observed even when extracellular cations are Ca2+. La3+ (1 mM), Cd2+ (1 mM) completely abolished the vasopressin-induced (IN.S.), however, nifedipine (10 microM) failed to inhibit it significantly. Single channel activities were recorded in the cell-attached configurations when vasopressin or endothelin-1 was applied to the bathing solution. The unitary conductance of the channels was approximately 20 pS with 140 mM Na+, Cs+, or K+ in the pipette, but was 15 pS with 110 mM Ca2+ in the pipette. Permeabilities sequence calculated from the reversal potentials was Na+ not equal to Cs+ not equal to K+ > Ca+. These results provide evidence that calcium entry and membrane depolarization elicited by vasopressin or endothelin-1 are mediated by a receptor-mediated Ca(2+)-permeable non-selective cation channel in aortic smooth muscle cells.

Tumor necrosis factor alpha and lymphotoxin stimulate human myeloblastic leukemia cell (ML-1) invasion through a reconstituted basement membrane (Matrigel) with concomitant induction of 92 kDa gelatinase secretion

We have examined the effects of tumor necrosis factor alpha (TNF) and lymphotoxin (LT) on gelatinase (72 kDa and 92 kDa) and tissue inhibitor of metalloprotease 1 (TIMP1) secretion by human myeloblastic leukemia cells (ML-1) in vitro. TNF (0.1-30 ng/ml) significantly stimulated 92 kDa gelatinase secretion in a dose-dependent manner, but did not significantly stimulate 72 kDa gelatinase secretion. LT also significantly stimulated 92 kDa gelatinase secretion, but the stimulation was less effective compared to TNF. TNF, but not LT, concentrations at 30 ng/ml slightly stimulated TIMP1 secretion. Because 92 kDa gelatinase is thought to play a pivotal role in tumor invasion, we examined the effect of TNF or LT on ML-1 cell invasion through a reconstituted basement membrane (Matrigel). Exposure of ML-1 cells to TNF (3, 10, and 30 ng/ml) or LT (3, 10, and 30 ng/ml) stimulated ML-1 cell invasion through Matrigel in a dose-dependent manner in vitro. The data suggest that TNF- and LT-stimulated 92 kDa gelatinase secretion could play an important role in TNF- or LT-stimulated ML-1 cell invasion.

Analytical studies of spontaneous and vasopressin-induced calcium oscillations in cultured vascular smooth muscle cells

Spontaneous and vasopressin-induced Ca2+ oscillations in cultured vascular smooth muscle (A7r5) cells were further examined and characterized. Intracellular Ca2+ concentrations ([Ca2+]i) were measured by use of a high-performance laser cytometer. When the oscillatory patterns in [Ca2+]i were analyzed with a power spectrum method, about 80% of cells exhibited spontaneous Ca2+ oscillations with the frequency of 0.02-0.5 Hz. Nifedipine abolished these repetitive spikes, whereas pinacidil partially attenuated their amplitude and frequency. When vasopressin (100 nM) was applied to A7r5 cells, there was an initial rise in [Ca2+]i, followed by a delayed sustained increase in [Ca2+]i. The one-pool, nonoscillatory model was employed to fit this biphasic change, and the difference between the observed response and the simulated response was then analyzed with a power spectral method. About 50% of cells were noted to display oscillatory patterns in [Ca2+]i after sustained increase in [Ca2+]i. The present study indicates that spontaneous Ca2+ oscillations in A7r5 cells are modulated by the activity of ATP-sensitive K+ channels and are not related to pertussis toxin-sensitive GTP-binding protein(s). On the basis of the one-pool, nonoscillatory model, it is suggested that the buffering capacity of internal stores appears to be stronger in the cells with spontaneous Ca2+ oscillations than in those in a quiescent state, and the vasopressin-mediated inhibition of accumulation by internal stores was attenuated when the cells exhibited spontaneous Ca2+ oscillations. The implementation of this minimum kinetic model integrated with a power spectrum method would be an alternative to understand the oscillating behavior in [Ca2+]i.

Dolichyl phosphate, a potent inducer of apoptosis in rat glioma C6 cells

Exposure of rat glioma C6 cells to dolichyl phosphate resulted in cell shrinkage followed by nuclear fragmentation and internucleosomal cleavage of genomic DNA, yielding ladder patterns of oligonucleosomal fragments, all characteristics of apoptosis. This phenomenon occurred in a dose and time dependent manner. Dolichol and prenol failed to induce apoptosis. The inhibitors of N-glycosylation, tunicamycin and swainsonine had no apparent effect on dolichyl phosphate-induced apoptosis. Apoptotic changes were also observed in HL-60 cells, SIRC cells and HeLa cells. Thus, dolichyl phosphate functions as a potential apoptosis inducer as well as an essential carrier lipid in the biosynthesis of N-linked glycoprotein.

Modulation of elastin expression by heparin is dependent on the growth condition of vascular smooth muscle cells: up-regulation of elastin expression by heparin in the proliferating cells is mediated by the inhibition of protein kinase C activity

The effect of heparin on elastin expression in the proliferating and quiescent phases of growth of smooth muscle cells was studied. Heparin stimulated elastin synthesis and its mRNA level 2-3 fold in the proliferating cells while it inhibited the cell proliferation. The inhibition of cell proliferation and the stimulation of elastin expression by heparin in the proliferating cells were mimicked by a potent protein kinase C antagonist, H-7, but not by H-89, W-7, and HA1004, suggesting that the effect of heparin is mediated by the inhibition of protein kinase C. In contrast, heparin inhibited elastin synthesis and its mRNA level slightly but exhibited no effect on cell proliferation in the growth-arrested cells. This result indicates that heparin reciprocally affects elastin expression depending on the growth state of smooth muscle cells. Heparin thus exerts a complex influence on elastin expression in smooth muscle cells.

Stimulation of cell proliferation and autoregulation of elastin expression by elastin peptide VPGVG in cultured chick vascular smooth muscle cells

Synthetic elastin peptides, VPGVG or its polymer (VPGVG)n, enhanced the proliferation of smooth muscle cells 1.5-fold during 48 h treatment at the concentrations over 10(-6) M or 1.0 microgram/ml, respectively. Monomeric and polymeric VPGVG sequences reduced elastin synthesis and its mRNA level to one-third and one-half of control respectively under the conditions in which the proliferation of cells were enhanced, but did not change collagen synthesis as measured by bacterial collagenase digestion. The elastin-specific autoregulation by elastin fragments may reflect the feedback regulation of elastin expression which may play an essential role in elastin metabolism under the normal and diseased conditions.

Cell cycle-dependent regulation of elastin gene in cultured chick vascular smooth-muscle cells

A study was made of the relationship between elastin expression and the proliferative state of chick vascular smooth-muscle cells. Confluent cells of primary culture brought to a quiescent state by the deprivation of serum for 72 h exhibited a 5-, 3.5- and 2-fold increase in elastin synthesis, elastin mRNA level and transcriptional activity of elastin gene respectively over those in the proliferative state. On re-addition of serum in serum-deprived culture, cells started to proliferate, and elastin synthesis, its mRNA level and transcription of the gene decreased to the level of a proliferative state within 24 h, indicating that elastin expression in smooth-muscle cells was controlled by their growth states at least in part at a transcriptional level. A comparable increase in elastin mRNA level was observed when the cell growth was arrested by suspension culture for 72 h. When the cells were synchronized at the G1/S phase with thymidine/hydroxyurea treatment, elastin expression at the G1/S phase was greater than that at the G2/M phase during cell cycling. Elastin mRNA level at the G0 phase brought about by serum-deprivation or suspension culture predominated over that at the G1/S phase during cell cycling. These results indicate that gene expression of elastin and cell cycle are tightly coupled, which is independent of the presence of serum or adhesive state, and that elastin expression could be a biochemical marker for the growth states of smooth-muscle cells.

Changes in the level of 7 alpha-hydroxy-3-oxo-4-cholestenoic acid in cerebrospinal fluid after subarachnoid hemorrhage

A high concentration of a type of cholic acid, 7 alpha-hydroxy-3-oxo-4-cholestenoic acid, is observed in the content of chronic subdural hematoma. To investigate the possible causes, the level of this compound was measured in the cerebrospinal fluid of patients who underwent surgery for aneurysmal subarachnoid hemorrhage or non-hemorrhagic diseases. The maximum level was significantly higher in the aneurysmal subarachnoid hemorrhage patients, indicating that surgical intervention did not cause the postoperative increase in the level of this compound in the cerebrospinal fluid. Monitoring of plasma levels showed no postoperative increase. In vitro culture of a mixture of arterial blood and cerebrospinal fluid failed to show the de novo production of this compound. These results strongly suggest extrahepatic intracranial production of this cholic acid occurs in subarachnoid hemorrhage. The high concentration of this compound in both chronic subdural hematoma and subarachnoid hemorrhage suggests a possible role for 7 alpha-hydroxy-3-oxo-4-cholestenoic acid in intracranial hemorrhagic disorders.

Enhanced tropoelastin-degrading activity during cell passages in cultured smooth muscle cells

Tropoelastin expression in vascular smooth muscle cells during serial cell passages from the primary to the tertiary culture was studied. The level of tropoelastin was found to be greatly reduced as the number of cell passages increased. The translational activity and level of elastin mRNA were essentially unchanged throughout the cell passages. The reduction in tropoelastin expression was not due to the repetitive trypsin treatment nor to the prolyl hydroxylation level of the newly-synthesized elastin. A comparable decline in tropoelastin expression was also found with increasing cell division in the primary cultures plated at different cell densities. A pulse-chase experiment revealed that the newly-synthesized elastin in the tertiary culture degraded more rapidly than that in the primary culture. The culture medium harvested from the tertiary culture exhibited a higher tropoelastin-degrading activity than that from the primary culture in the test-tube. The degrading activity of the tertiary culture was inhibited by the addition of 1 mM ethylenediaminetetraacetic acid or 1 mM phenylmethylsulfonyl fluoride, but not by 1 mM N-ethylmaleimide. These results suggest that the reduction in tropoelastin expression during the cell passages from the primary to the tertiary culture is due to the enhanced tropoelastin-degrading activity of the tertiary culture. The transition to tropoelastin-degrading phenotype during cell passages may explain the biological mechanisms of smooth muscle cell migration from the media to the intima observed in the pathological conditions.

Ornithine decarboxylase is directly involved in mouse mammary carcinoma cell invasion in vitro

To elucidate the role of ornithine decarboxylase (ODC) in cancer cell invasion, we have compared the invasiveness of mouse mammary carcinoma, FM3A and its variant cell line, EXOD, which overproduces ODC. We have found that EXOD cells showed about 5.6-fold more invasiveness through a reconstituted basement membrane (Matrigel) compared to FM3A cells. To elucidate the underlying mechanism of increased invasiveness of EXOD cells, we analyzed gelatinase activity in conditioned media derived from FM3A and EXOD cells. EXOD cells secreted approximately 3-fold 72kDa gelatinase compared to FM3A cells. Cell attachment ability to Matrigel was also studied. Although FM3a and EXOD cells showed increased attachment to Matrigel in a dose-dependent manner, EXOD cells showed higher cell attachment ability compared to FM3A cells. Anti-72kDa gelatinase neutralizing antibody suppressed EXOD cell invasion through Matrigel. Further, antisense oligonucleotides of ODC suppressed EXOD cell invasion through Matrigel. Although the causal relationship among ODC expression, gelatinase secretion and cell attachment ability remains to be elucidated, the results suggest that both overproduction of ODC and 72kDa gelatinase secretion are directly involved in increased invasiveness of EXOD cells.

Sexual dimorphism of lipids in Harderian glands of golden hamsters

The Harderian gland of golden hamsters excretes alkyldiacylglycerol (ADG), the fatty acid and alkyl compositions of which differ between males and females. ADG in males contains mostly straight chain fatty acids, even- and odd-numbered, the major one being 15:0, while ADG in females contains iso- and anteiso-branched chain acids (34.0%). Iso-branching was found in both even- and odd-numbered acids, but anteiso-branching was found mostly in odd-numbered acids. The presence of propionic acid at the 3 position of the glycerol moiety in male ADG, and of isovaleric and 2-methylbutyric acids at the same position in female ADG was demonstrated by NMR spectrometry. Alkyl portions also exhibited sexual dimorphism in these lipids. ADG from males consisted of straight aliphatic chains, but branched chain components occupied almost half (45%) in ADG from females, and the branching resided at the iso- and anteiso-positions. The ADGs in glands from the two sexes were separated by Iatrobeads column chromatography into three and two subfractions, respectively. The fatty acid and alkyl compositions of these subfractions coincided with the above-mentioned results and with the behavior of the ADGs on thin-layer plates. These findings suggest that a sex hormone affects the metabolism of valine, leucine and isoleucine, and sexual dimorphism of ADGs occurs in the Harderian gland.

Induction of Ca2+ oscillations by vasopressin in the presence of tetraethylammonium chloride in cultured vascular smooth muscle cells

The change of cytosolic Ca2+ concentration ([Ca2+]i) caused by vasopressin was examined in indo-1-loaded A7r5 smooth muscle cells by use of the high-performance laser cytometer and ratiometric fluorescence method. Vasopressin (100 nM) caused an initial rapid rise and a delayed increase in [Ca2+]i (n = 6). However, in the presence of tetraethylammonium chloride (10 mM), vasopressin consistently triggered sustained Ca2+ oscillations which were preceded by a large peak of [Ca2+]i. The latency for the development of this huge increase in [Ca2+]i prior to the occurrence of sustained Ca2+ oscillations was always the same. The frequency and amplitude of this type of Ca2+ oscillation varied depending upon the extracellular Ca2+ concentration. Ca(2+)-free solution did not completely suppress the sustained Ca2+ oscillations, but caffeine (20 mM) effectively abolished them. The present findings indicate that in A7r5 smooth muscle cells, the sustained Ca2+ oscillations triggered by vasopressin in the presence of tetraethylammonium chloride were mainly due to Ca2+ release from IP3-sensitive Ca2+ stores and Ca2+ influx from extracellular space, and did not require the pacemaker activity derived from the surface membrane. Moreover, the vasopressin-induced change in [Ca2+]i appeared to be linked to pertussis toxin-insensitive GTP-binding protein(s).

Comparison of ELISA and HPLC for the determination of desmosine or isodesmosine in aortic tissue elastin

We developed a rapid and simple method for estimating tissue elastin content by measuring desmosine (D) in tissue hydrolysates by competitive ELISA. We compared the ELISA previously reported HPLC methods. When D or isodesmosine (ID) in hydrolysate of the same elastin preparation were measured by the two different methods, a good linear relationship was obtained (r = 0.854 for human aorta or r = 0.938 for rabbit aorta, respectively). The ELISA method can detect as little as 6 pmol/ml and it may be useful in monitoring elastin metabolism in patients with various connective tissue diseases.

Important contribution of the methylene part of LTB4 toward binding affinity to the LTB4 receptors and rise in intracellular-free calcium concentration

In order to examine a role of the C(16)-C(20) methylene part of leukotriene B4 (LTB4) toward the activation of leukocytes, we synthesized the LTB4-analogues in which the length of the C(16)-C(20) part of LTB4 is varied systematically while the two hydroxyl groups at C(5) and C(12) positions and the 6(Z), 8(E), 10(E) conjugated triene unit remained untouched. We examined their binding affinity to the LTB4 receptors present in the rat polymorphonuclear leukocytes (PMNLs) and their ability to raise intracellular-free calcium concentration ([Ca2+]i) in the rat PMNLs loaded with fura-2. As the length of the chain of LTB4 was increased or decreased one by one, the binding affinity to the LTB4 receptors diminished, and the analogues of more than three carbon atoms shorter chain were of about three log order less activity than LTB4. The biological potency as assessed in [Ca2+]i rises pararelled that of the binding affinity to the PMNL membrane. These results indicate that the C(16)-C(20) part of LTB4 plays important role for the activity. In a similar way we prepared the LTB4-analogues of a different chain length between C(2)-C(4) of LTB4 and tested their biological activity. We found that the C(2)-C(4) part of LTB4 also affects the activity.

Distribution of cholinergic neuron-specific gangliosides (GT1a alpha and GQ1b alpha) in the rat central nervous system

A newly developed mouse monoclonal antibody, GGR-41, was used to localize a novel species of gangliosides, GT1a alpha and GQ1b alpha, in the rat central nervous system. Intense immunoreactivity was found in the neuropil of the spinal cord dorsal horn, spinal trigeminal nucleus, solitary tract nucleus, superior colliculus, interpeduncular nucleus, hypothalamus and septal area. The results suggest that GT1a alpha and GQ1b alpha are expressed in the nerve terminals of a certain population of cholinergic fibers.

Biosynthetic pathway for a new series of gangliosides, GT1a alpha and GQ1b alpha

A new class of gangliosides, GT1a alpha and GQ1b alpha, were initially identified as cholinergic neuron-specific antigens in bovine brain. These gangliosides have in common alpha 2-6 NeuAc linked to the GalNAc residue in the gangliotetraose core structure. In this study, we have determined the biosynthetic pathways of GT1a alpha and GQ1b alpha using rat liver Golgi fraction. The results showed that GT1a alpha and GQ1b alpha were synthesized from GD1a and GT1b, respectively, by the action of a GalNAc alpha 2-6 sialyltransferase. It was also demonstrated that these two gangliosides were found to exist as extremely minor components in rat liver.

Two species of antiganglioside antibodies in a patient with a pharyngeal-cervical-brachial variant of Guillain-Barré syndrome

A patient with a pharyngeal-cervical-brachial variant of Guillain-Barré syndrome had anti-GT1a and anti-GD1a antibodies (IgG) in the serum. The activities of anti-GT1a antibodies were stronger than anti-GD1a antibodies and their activities declined later in the clinical course. These two different antibodies bound independently to each ganglioside in an absorption study with polystyrene beads coated with GT1a or GD1a.

[Effect of traditional Chinese medicine (dai-saiko-to) on experimental calcinosis]

To clarify the anti-calcinosis actions of traditional Chinese medicine (Dai: Dai-saiko-to) and estradiol benzoate (E2), 7-week or retired (about 6-months-old) female rats were treated with Vit. D2 (1.75 x 10(5) I.U./kg b.w./day) for 4 days, and then were fed a basal diet containing Dai (at ten times the medical dose in humans) or were injected i.p. with E2 (at the medical dose in humans) for 6 weeks. The following results were obtained: 1) Dai did not improve Ca and P metabolism in experimental calcinosis of 7-week female rats; 2) in retired female rats, Dai decreased both P in the heart and the ratio of Ca to P in bone, similar to the treatment with E2. Dai, as well as E2, seemed to nomalize Ca and P metabolism disturbed by Vit. D2 treatment.

Identification of new mutations in sterol 27-hydroxylase gene in Japanese patients with cerebrotendinous xanthomatosis (CTX)

Cerebrotendinous xanthomatosis (CTX) is a hereditary sterol storage disease associated with accumulation of cholesterol and cholestanol in various tissues, especially tendons and neural tissues. The biochemical defect that causes CTX is a deficiency of the mitochondrial sterol 27-hydroxylase which oxidizes the side chain of cholesterol in connection with formation of bile acids. Japan has a relatively high prevalence of CTX and more cases of the disease are found here than in any other country. In the present study two new different point mutations are described in the heme-ligand binding domain of the sterol 27-hydroxylase gene in three Japanese CTX patients and one CTX heterozygote. Two of the homozygotes as well as the heterozygote subject have a single base substitution of A for G at codon 441 [CGG (Arg) to CAG (Gln)]. Another homozygote has a transition of C to T at codon 441 [CGG (Arg) to TGG (Trp)]. These two different mutations result in two restriction fragment length polymorphisms (RFLPs) for the enzymes StuI or HpaII. We also assayed sterol 27-hydroxylase activity using skin fibroblasts derived from three CTX patients, one CTX heterozygote, and normal subjects. While two of the homozygous subjects have undetectable levels of the enzyme activity, one homozygous subject and one heterozygous subject have decreased levels of the enzyme activity, about 1.4% and 10% of normal, respectively. The results suggest that the newly identified point mutations in the sterol 27-hydroxylase gene could account for the sterol 27-hydroxylase deficiency in the Japanese CTX patients.

Biochemical analyses of macromolecular matrix components in patients with pseudoxanthoma elasticum

Two cases of pseudoxanthoma elasticum (PXE) were reported. Biochemical studies of collagen, glycosaminoglycan, and elastin content were performed using skin specimens from affected lesions. Hydroxyproline content was reduced approximately 46% and 24% in cases 1 and 2, respectively. The reduction in collagen content resulted from the reduction in the lower dermis, not from that in the upper dermis. Glycosaminoglycan content in PXE was also decreased, with a slight increase in the ratio of hyaluronic acid to dermatan sulfate. Isodesmosine content in PXE was increased 3.2- and 2.2-fold in cases 1 and 2, respectively. These results suggest that the major and primary biochemical changes in PXE are an increase in elastin content.

1-Alkyl-2,3-diacylglycerol synthesis in primary culture cells of guinea pig harderian gland

Using a primary culture system of guinea pig Harderian gland cells, we investigated the metabolism of a unique lipid: 1-alkyl-2,3-diacylglycerol containing methyl-branched fatty acids. The cells were obtained by collagenase digestion, and cells with lipid-droplets were collected by two-step centrifugation. We cultured these cells, and examined their lipid and fatty acid compositions. The de novo synthesis of lipids in these cells was studied as to the incorporation of [1(2)-14C]acetate and [U-14C]glucose. The major lipid proved to be 1-alkyl-2,3-diacylglycerol, as in tissue, and it contained a large amount of methylbranched fatty acids specific to this gland. The incorporation of [14C]acetate and [14C]glucose into 1-alkyl-2,3-diacylglycerol in the cultured cells amounted to 79.7 and 88.2% of the total incorporation into the lipid fraction, respectively. The incorporation of [14C]acetate into fatty acids in the cultured cells was detected for the chain lengths of C14 to C25. The activities of glycerol-3-phosphate dehydrogenase in the cultured cells and Harderian gland were lower than that in adipose tissue. These results confirm that cultured cells reflect the lipid metabolism originating in the Harderian gland and show that this culture system can serve as one part of the armamentarium for further study of this unique lipid metabolism.

Gallstone formation in cholestanol-fed mice

We examined the effect of cholestanol (5 alpha-dihydrocholesterol) on cholesterol and bile acid metabolism in BALB/c mice. After feeding 1% cholestanol in the diet for 14 months, gallstones composed of 55% cholesterol and 45% cholestanol developed in 20% of the mice and were associated with mucosal inflammation and serosal vessel thickening of the gallbladder. Cholestanol concentrations increased 42-fold in the serum (0.17 versus 0.004 mg/ml) and 18-fold in the liver (0.55 versus 0.03 mg/g) as compared with control mice, whereas cholesterol declined 20 and 26% in serum and liver, respectively. Hepatic microsomal HMG-CoA reductase activity, reflecting cholesterol synthesis, rose 51% (from 7.2 to 10.9 pmol/mg/min). In contrast, hepatic microsomal cholesterol 7 alpha-hydroxylase activity, the rate-determining enzyme for bile acid synthesis, was severely depressed as compared with control mice (0.9 versus 2.2 pmol/mg/min). Discontinuing cholestanol from the diet for 1 month reduced the elevated serum and liver cholestanol concentrations and restored hepatic HMG-CoA reductase and cholesterol 7 alpha-hydroxylase activities to normal. These results demonstrate that cholestanol is absorbed, replaces cholesterol in serum and liver, causes increased cholesterol synthesis, but inhibits bile acid synthesis. The combination of increased cholesterol synthesis with decreased bile acid formation promotes gallstone formation in cholestanol-fed mice.

Initiation of DNA synthesis in a high molecular weight fraction of Xenopus egg extract

Xenopus egg extract was fractionated by gel-filtration column chromatography and DNA synthetic activity was examined using double-stranded DNA as a template. The major activity eluted had an apparent molecular mass of about 300 kDa. Product analyses showed that de novo DNA synthesis occurs with formation of replication bubbles, thereby suggesting that this fraction catalyzes the initiation of DNA replication. Activities of DNA polymerase alpha-primase and DNA helicase overlapped with the DNA synthetic activity, but the elution profiles of the enzymes differed from that of the DNA synthetic activity. Therefore, this 300-kDa fraction may contain a component which differs from the above enzymes yet is essential for initiation of DNA replication.

Three types of Gi alpha protein of the guinea-pig lung: cDNA cloning and analysis of their tissue distribution

cDNA clones encoding three types of Gi alpha, the alpha subunit of GTP-binding protein (Gi1 alpha, Gi2 alpha, and Gi3 alpha), were isolated from a cDNA library of the guinea-pig lung. Nucleotide sequence analysis revealed a high degree of homology with other mammalian Gi alpha cDNAs. By RNA blot analysis, the expression pattern of Gi1 alpha was more tissue-specific than those of other types of Gi alphas in the guinea-pig tissues examined. While Gi2 alpha and Gi3 alpha mRNAs were ubiquitously expressed in all tissues examined, Gi1 alpha mRNA was mainly expressed in the brain, lung and kidney. These results suggest that each Gi alpha protein may have a different role.

[Effects of traditional Chinese medicines (dai-saiko-to, sho-saiko-to and hachimi-zio-gan) on spontaneously diabetic rat (WBN/Kob) with experimentally induced lipid and mineral disorders]

To clarify the therapeutic effects of several traditional Chinese medicines to improve disorders of carbohydrate, lipid and mineral metabolism, spontaneously diabetic rats (WBN/Kob) were treated with Vit. D2, 1 x 10(5) I.U./kg b.w./day, for 4 days, and then fed a hyperlipidemic diet containing traditional Chinese medicines for 6 weeks. The following results were obtained: 1) In the diabetic rats, the 3 traditional Chinese medicines further decreased the blood glucose level at 120 min after glucose loading in the glucose tolerance test. 2) The drugs increased the inorganic phosphate in the liver and normalized mineral metabolic disorder. 3) Hachimi-zio-gan decreased the cholesterol content in the kidney, and Sho-saiko-to decreased the cholesterol content in the elastin fraction (elastin-cholesterol) of the kidney. Such experimental results suggest that traditional Chinese medicines may be effective against the pathological conditions of diabetes mellitus that involve disorders of lipid and mineral metabolism.

Effect of Harderian gland-derived growth factor on the growth of cornea stromal cells

To investigate the physiological role of Harderian gland-derived growth factor (HGDGF), the effects of HGDGF and various other growth factors on the growth of cultured guinea pig cornea stromal cells were examined. HGDGF increased the incorporation of [3H]thymidine to 150% of the control (5% fetal calf serum). The combination of HGDGF with fibroblast growth factors (FGFs) or platelet-derived growth factor enhanced the cell growth over that of either growth factor alone, increasing the incorporation of [3H]thymidine to 180 and 190% of the control, respectively. The combination of HGDGF with transforming growth factor (TGF-beta) decreased the growth to 60% of the control, and epidermal growth factor had no effect on the activity of HGDGF. The growth-stimulating activity of HGDGF was inhibited by suramin in a different manner from that of FGFs. These findings suggest that HGDGF binds a specific cell-surface receptor and plays a role in the repair of injured parts of the cornea and in the maintenance of the cornea stromal cells.

Platelet-activating factor (PAF) receptor in rat brain: PAF mobilizes intracellular Ca2+ in hippocampal neurons

Platelet-activating factor (PAF), an alkylether phospholipid, is produced in the brain when it is subjected to various stimuli. Using a Xenopus oocyte expression system, we obtained evidence for functional PAF receptor mRNA expression in rat brain. The presence of the PAF receptor was confirmed and shown to be quite ubiquitous in the CNS by RNA blot and radioligand binding studies. To investigate the neuronal functions of PAF, intracellular Ca2+ increase elicited by nanomolar PAF application was analyzed in cultured rat hippocampal cells. Fractions of NMDA-responsive cells and non-NMDA-responsive cells were shown to respond to PAF, suggesting a potential role for PAF in the Ca2+ signaling pathway in the hippocampus.

Identification of 7 alpha-hydroxy-3-oxo-4-cholestenoic acid in chronic subdural hematoma

We detected a novel kind of bile acid in the content of chronic subdural hematoma. This substance was specifically found in chronic subdural hematoma, and not in subdural hygroma, which is pathologically similar except for the lack of capsular membrane. The compound was identified as 7 alpha-hydroxy-3-oxo-4-cholestenoic acid by high performance liquid chromatography, gas chromatography-mass spectrometry, and nuclear magnetic resonance spectrometry. The structure was confirmed by the comparison with the chemically synthesized compound. The average contents in chronic subdural hematoma were 658.09 +/- 137.53 ng/ml, while those in normal human plasma were 126.27 +/- 17.73 ng/ml. It was not detected in normal cerebrospinal fluid. The higher level in chronic subdural hematoma than human plasma strongly suggests the local, extrahepatic production of this type of C27 bile acids.

Properties of the guinea-pig lung platelet-activating factor receptor encoded by the cloned cDNA

Platelet-activating factor (PAF) is a naturally occurring phospholipid possessing proinflammatory and shock-inducing activities. Although PAF exerts these functions via specific receptors, the molecular structures of the receptor has not been clarified. We have isolated a cDNA coding for PAF receptor through expression cloning. The PAF receptor expressed in Xenopus laevis oocytes and COS-7 cells showed pharmacological properties consistent with those in previous reports. Sequence analysis revealed that PAF receptor belongs to the superfamily of G-protein-coupled receptors.

Characterization of prostaglandin and thromboxane receptors expressed on a megakaryoblastic leukemia cell line, MEG-01s

MEG-01s, an established human megakaryoblastic leukemia cell line, exhibited specific high-affinity binding sites for [3H]iloprost, a stable prostaglandin (PG) I2 analogue, for [3H]SQ-29548, a stable thromboxane (TX) A2 antagonist and, for [3H]PGE2/PGE1, but not for [3H]PGD2. In the MEG-01s cells, iloprost/PGI2, or PGE1 stimulated cAMP production with ED50 values practically identical to the IC50 values for the [3H] iloprost binding. STA2 and U46619, TXA2/PGH2 agonists, PGE2/PGE1, iloprost/PGI2, and thrombin elevated the intracellular concentrations of Ca2+ ([Ca2+]i), as determined by Fura-2 fluorescence signals. Elevation of [Ca2+]i by PGE2/PGE1 and iloprost, but not that by TX-agonists or thrombin, was totally dependent on the presence of extracellular Ca2+. This effect by PGE2/PGE1 was partially inhibited by prior treatment of the cells with islet-activating protein (IAP), while that by TX-agonists or by PGI2/iloprost was not affected. We tentatively conclude from these results that: (1) MEG-01s cells express (a) PGI2/PGE1 receptor(s) coupled to adenylate cyclase and Ca2+ influx, a TXA2/PGH2 receptor coupled to the phosphatidylinositol-turnover-Ca2+ system, and the PGE2/PGE1 receptor coupled to Ca2+ influx; (2) the receptors for TXA2/PGH2 and iloprost and those for PGE2/PGE1 and thrombin are coupled to IAP-insensitive and IAP-sensitive GTP-binding proteins, respectively, and function in a different manner to elevate [Ca2+]i. Thus, the MEG-01s cell line is a pertinent model for studying eicosanoid receptor-mediated signal transduction in platelet/megakaryocyte systems.

The differences in 12-hydroxyeicosatetraenoic acid and thromboxane B2 release from guinea pig platelets

Anti-12(S)-hydroxyeicosatetraenoic acid (12-HETE)-antibody and anti-thromboxane B2 (TXB2)-antibody were generated and applied to the radioimmunoassay. The detection limit for 12-HETE was 16 pg. The cross-reactivities of anti-12-HETE-antibody were 4.6% for 15-HETE, 0.18% for 5-HETE and below 0.15% for leukotrienes and prostaglandins (PGs). 12-HETE and TXB2 released from guinea pig platelets were measured by radioimmunoassay. Platelet activating factor (PAF) at 10(-9) M induced the aggregation of platelets, the releases of immunoreactive-12-HETE (1.8 +/- 1.2 ng/10(8) platelets, mean +/- S.D.) and immunoreactive-TXB2 (18.5 +/- 17.3 ng/10(8) platelets). Collagen at 1 microgram/ml also evoked platelet aggregation, the releases of immunoreactive-12-HETE (2.7 +/- 1.1 ng/10(8) platelets) and immunoreactive-TXB2 (11.8 +/- 4.6 ng/10(8) platelets). By the stimulation with these compounds, TXB2 was produced in a greater amount than 12-HETE from guinea pig platelets. Although 10(-7) M and 10(-6) M U46619, a TXA2 mimetic, caused platelet aggregation, arachidonic acid metabolites were not released. These data suggest the presence of different mechanisms of platelet activation depending on each stimulus.