Two-dimensional configuration of the myoneural junctions of human masticatory muscle detected with matrix electrode

Motor unit action potentials (MUAPs) propagate bidirectionally from the myoneural junction along the muscle fibre. The propagation of excitation within single motor units can be detected during sustained isometric contraction using a surface electrode array. Electromyographic (EMG) signals from an adjacent pair of contacts along the muscle fibres show a very similar wave form with a time shift. In the present study, EMG signals of the masseter and the temporal muscles were obtained from two male adults during clenching in the intercuspal position using the multichannel surface electrode with 17 x 11 contacts. The two-dimensional location of the myoneural junction for each column from the source of the propagation was estimated. Each of the myoneural junctions was located in the lower portion of the masseter muscle and in the upper portion of the temporal muscle. However, the junction was distributed within 10 mm along the muscle fibres at different contraction levels in each muscle. This noninvasive technique of multiple surface electrodes enabled us to add to knowledge of the anatomical structure of the masticatory muscles examined.

Anterior chamber angle biometry: quadrant variation, age change and sex difference

PURPOSE

To estimate the anterior change angle width (ACAW) in healthy volunteers quantitatively using an anterior eye segment analysis system and to clarify the involvement of aging and sex in ACAW.

METHODS

The ACAW of the upper, lower, medial, and lateral quadrants of 42 eyes from 42 healthy volunteers was measured by the NIDEK EAS-1000 anterior eye segment analysis system, a non-invasive in vivo measuring method based on Scheimpflug image analysis. Data from all subjects were employed to investigate aging and quadrant differences; and age-matched male and female subjects were chosen from all subjects to study sex difference and aging.

RESULTS

Young subjects showed no significant inter-quadrant differences of ACAW. However, ACAW showed a significant negative correlation with age in all quadrants, but the lateral quadrant showed much more narrowing than the others. The age-matched study revealed that ACAW narrowing was much greater in females than in males, and a polynomial regression analysis showed that this sex difference appeared in subjects older than middle age.

CONCLUSIONS

The anterior eye segment analysis system revealed that ACAW decreased with age, especially in the lateral quadrant. The significantly more marked narrowness of ACAW in females older than middle age may be related to the high incidence of angle closure glaucoma in elderly females.

Inhibitor and temperature effect on catalase in the liver of adult diploid and haploid Rana rugosa

The authors succeeded in raising a single mature haploid Rana rugosa female to the age of 2 years from an egg artificially fertilized with ultraviolet-irradiated sperm. In order to discover why this particular haploid individual should survive so long, hydrogen peroxide detoxifying catalase in the liver of this individual and age-matched diploids was examined and compared for total activity, temperature stability, and chemical inhibition. Total activity was found to be significantly higher in the haploid frog than in the diploids, suggesting that this particular haploid had a unique system for hydrogen peroxide detoxification which protected the liver against cell death, preventing hepatic failure, and leading to a prolonged survival. Liver catalase from the haploid proved to be more labile to aminotriazole and urea, losing 60-70% of its original activity after 30 min treatment, whereas diploid catalase lost only 40% under the same conditions. Haploid and diploid catalase responded similarly to heat, however. It seems likely that inhibitor-binding sites differ considerably between the catalase of normal diploids and the catalase of this particular haploid, while overall structure is generally similar.

Crystallization and preliminary X-ray analysis of the periplasmic receptor (PotF) of the putrescine transport system in Escherichia coli

The primary receptor (PotF) of the putrescine transport system in E. coli has been crystallized by the hanging-drop vapor-diffusion technique. The crystals belong to the space group P21212 with unit-cell dimensions a = 269.4, b = 82.33 and c = 93.74 A. The crystals diffract beyond 2.2 A with a rotating-anode X-ray source. A complete data set from the native crystals has been collected and processed at 2.3 A resolution. Two heavy-atom derivatives have been prepared from the same Pt compound at 293 and 277 K. The difference Patterson maps revealed completely different major heavy-atom sites between these two derivatives.

Prostaglandins increase matrix metalloproteinase release from human ciliary smooth muscle cells

PURPOSE

To identify matrix metalloproteinases (MMPs) released by ciliary smooth muscle cells in vitro and to determine whether MMP release is altered by exposure to prostaglandins (PGs).

METHODS

Human ciliary smooth muscle cells were grown to confluence in monolayer cultures and treated with PGF2 alpha, 11-deoxy-PGE1, or PhXA85 (the nonesterified analogue of PhXA41) for 12 to 72 hours. The activity of MMP in the medium was assayed using gelatin and casein zymography. Identification of the specific MMP associated with each band was made by Western blot analysis. Band intensity, which reflects activity, was measured with a scanning laser densitometer.

RESULTS

Three major bands appeared in the gelatin zymographs at positions corresponding to molecular weights of 62 kDa, 68 kDa, and 97 kDa. A single band at 50 kDa predominated in the casein zymograms. Substitution of EDTA for calcium and zinc in the development solution eliminated the appearance of these bands, indicating that they reflect MMP activity. Immunoblotting, using MMP-specific antibodies, confirmed that the three bands in the gelatin zymographs were MMP-1, MMP-2, and MMP-9, respectively; the single band in the casein zymographs was MMP-3. Treatment with 200 nM PGF2 alpha, 11-deoxy-PGE1, or PhXA85 for 72 hours increased the combined density scores for MMP-1 and MMP-2 by 37%, 64%, and 27%; the density scores for MMP-9 by 268%, 253%, and 125%; and the density scores for MMP-3 by 35%, 71%, and 22%, respectively.

CONCLUSIONS

These results indicate that ciliary smooth muscle cells can secrete MMP-1, MMP-2, MMP-3, and MMP-9. In addition, exposure to PGF2 alpha, 11-deoxy-PGE1, or PhXA85 increases production of all four MMPs. These observations support the hypothesis that increased MMP production by ciliary muscle cells has a role in increasing uveoscleral outflow facility after topical PG administration.

Malignant transformation by overproduction of translation initiation factor eIF4G

N4G3, a cell line that overexpresses translation initiation factor eIF4G, one of the components of eIF4F, was made by stable transfection of the human eIF4G cDNA into NIH3T3 cells. The cells expressed 80-100 times greater levels of eIF4G mRNA than did NIH3T3 cells. N4G3 cells formed transformed foci on a monolayer of cells, showed anchorage-independent growth, and formed tumors in nude mice. These results indicate that overexpression of eIF4G caused malignant transformation of NIH3T3 cells. It is also known that overexpression of eIF4E, another component of eIF4F, causes transformation of NIH3T3 cells. However, there was no difference in the amount of eIF4E protein between N4G3 and NIH3T3 cells, indicating that cell transformation does not involve a change in eIF4E levels. The results may be due to an effect of eIF4G on translational control of protein synthesis directed by mRNAs having long 5'-untranslated region.

Benzyl-polyamines: novel, potent N-methyl-D-aspartate receptor antagonists

The effects of benzyl-polyamines were studied at recombinant N-methyl-D-aspartate (NMDA) receptors expressed in Xenopus laevis oocytes. A number of mono-, di- and tri-benzyl polyamines, having benzyl substitutions on the terminal or central amino groups, inhibited responses of NR1/NR2 receptors in oocytes voltage-clamped at -70 mV. Among the most potent compounds was N1,N4, N8-tri-benzyl-spermidine (TB-3-4), which had an IC50 value of 0.2 microM. TB-3-4 was approximately 40-fold more potent at NR1/NR2A and NR1/NR2B receptors than at NR1/NR2C or NR1/NR2D receptors. Block by TB-3-4 was strongly voltage dependent. Using voltage ramps analyzed by the Woodhull model of voltage-dependent channel block, TB-3-4 was found to have a Kd(0) value of 5 microM and a zdelta value of 1.41 at NR1/NR2B channels, whereas the affinity of binding [Kd(0) = 250 microM] but not the degree of voltage-dependence (zdelta = 1.43) was much lower at NR1/NR2D channels. At a concentration of 10 microM, TB-3-4 had no effect on alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors expressed from the GluR1 subunit, indicating that TB-3-4 is a selective NMDA antagonist. TB-3-4 did not permeate wild-type NMDA channels but could easily permeate channels containing an N616G mutation in the NR1 subunit. This mutation is presumed to increase the size of the narrowest constriction of the NMDA channel, thus allowing passage of TB-3-4. Benzyl-polyamines such as TB-3-4 represent a structurally novel class of NMDA receptor channel blockers.

Comparison of catalase in diploid and haploid Rana rugosa using heat and chemical inactivation techniques

The present study examines differences in the hydrogen peroxide (H2O2) detoxifying enzyme, catalase, found in the tails and livers of diploid and haploid Rana rugosa. Investigative techniques include measurement of catalase activity and tests for temperature stability and chemical inhibition. Catalase from the tails of pre-climactic (stage XXIII) haploids was found to be over three times as H2O2 destructive as catalase from similar tails of diploids. Catalase from the livers of newly metamorphosed (stage XXV) froglets, on the other hand, displayed only one third the activity seen in diploid livers. The catalase in haploid tail and liver proved to be more heat resistant, retaining 40-60% of its original activity after 5 min of treatment at 55 degrees C, whereas diploid catalase was totally inactivated under the same conditions. Haploid and diploid catalase also responded differently to inhibition using urea and aminotriazole. These differences suggest that haploid catalase has diverged from normal diploid catalase through molecular modification, resulting in abnormal systems for H2O2 metabolism, which in turn are thought to be responsible for organ dysfunction and early death seen in haploid individuals.

Block and modulation of N-methyl-D-aspartate receptors by polyamines and protons: role of amino acid residues in the transmembrane and pore-forming regions of NR1 and NR2 subunits

N-Methyl-D-aspartate (NMDA) receptors are modulated by extracellular spermine and protons and are blocked in a voltage-dependent manner by spermine and polyamine derivatives such as N1-dansyl-spermine (N1-DnsSpm). The effects of mutations in the first and third transmembrane domains (M1 and M3) and the pore-forming loop (M2) of NMDA receptor subunits were studied. Surprisingly, some mutations in M2 and M3 of the NR1 subunit, including mutations at W608 and N616 in M2, reduced spermine stimulation and proton inhibition. These mutations may have long-range allosteric effects or may change spermine- and pH-dependent gating processes rather than directly affecting the binding sites for these modulators because spermine stimulation and proton inhibition are not voltage dependent and are thought to involve binding sites outside the pore-forming regions of the receptor. A number of mutations in M1-M3, including mutations at tryptophan and tyrosine residues near the extracellular sides of M1 and M3, reduced block by spermine and N1-DnsSpm. The effects of these mutants on channel block were characterized in detail by using N1-DnsSpm, which produces block but not stimulation of NMDA receptors. Block by N1-DnsSpm was studied by using voltage ramps analyzed with the Woodhull model of channel block. Mutations at W563 (in M1) and E621 (immediately after M2) in the NR1A subunit and at Y646 (in M3) and N616 (in the M2 loop) in the NR2B subunit reduced the affinity for N1-DnsSpm without affecting the voltage dependence of block. These residues may form part of a binding site for N1-DnsSpm. Mutation of a tryptophan residue at position W607 in the M2 region of NR2B greatly reduced block by N1-DnsSpm, and N1-DnsSpm could easily permeate channels containing this mutation. The results suggest that at least parts of the M1 and M3 segments contribute to the pore or vestibule of the NMDA channel and that a tryptophan in M2 (W607 in NR2B) may contribute to the narrow constriction of the pore.

Prostaglandins alter extracellular matrix adjacent to human ciliary muscle cells in vitro

PURPOSE

This study investigates the possibility that prostaglandins (PGs) induce changes in extracellular matrix (ECM) adjacent to ciliary muscle cells.

METHODS

Human ciliary smooth muscle cells were grown to confluence in monolayer cultures and were treated with PGF2alpha, 11-deoxy-PGE1, or PhXA85 (the nonesterified analogue of PhXA41) for 12 to 72 hours. The amount of collagens type I, III, and IV in the cultures was determined, using sandwich enzyme immunoassays. The distributions of these collagens were assessed in the PG-treated cultures by immunocytochemistry.

RESULTS

Twenty-four-hour treatment with 20 nM PGF2alpha, 11-deoxy-PGE1, or PhXA85 reduced the amount of collagen type I in extracts of the cell layer by 65+/-10%, 56+/-7%, and 46+/-7%, respectively, when compared with levels of those substances in vehicle-treated cultures. In similar fashion, collagen type III in cell layer extracts was reduced by 41+/-5%, 33+/-9%, and 3+/-5%, respectively. When the concentration of PGs was increased to 200 nM, the amount of type III collagen in the cell layer extracts was reduced by 93+/-7%, 99+/-1%, and 99+/-1%, respectively. Changes in type IV collagen in cell layer extracts after treatment with 20 nM PGs were not statistically significant. When the concentration of PGF2alpha, 11-deoxy-PGE1, or PhXA85 was increased to 200 nM, the amount of collagen type IV in the cell layer extract increased by 101+/-16%, 14+/-5%, and 89+/-11%, respectively. There were minimal changes in the staining pattern for collagen type I after 24-hour treatment with 20 nM PGs. When the PG concentration was increased to 200 nM, there were reductions in the density of collagen type I fibrils and clumping of collagen type III immunoreactive elements. The delicate lacework of collagen type IV immunoreactivity was replaced by bundles or clumps of heavy immunoreactive strands, separated by areas without immunoreactivity. These changes were present in cultures exposed to 20 nM PGs and were marked when PG concentration was increased to 200 nM.

CONCLUSION

These results indicate that PGs can induce substantial changes in the ECM around ciliary smooth muscle cells in vitro. These data support the possibility that changes in ciliary muscle ECM may contribute to increased uveoscleral outflow facility after topical PG administration.

Identification of regulatory region of antizyme necessary for the negative regulation of polyamine transport

Antizyme is a negative regulator of ornithine decarboxylase (ODC) and of polyamine transport. Regions of antizyme necessary for the negative regulation of polyamine transport were determined by transfecting ODC-overproducing EXOD-1 cells with mutant antizyme genes containing different size deletions in the NH2- and COOH-terminal of antizyme (AZ69-227). When peptide 119-144 or peptide 211-216, which are responsible for the binding of ODC, were deleted from antizyme, the mutant antizyme could not reverse the inhibition of growth of EXOD-1 cells produced by spermine. In parallel with the decrease in antizyme effect on cell growth, spermine transport activity and the accumulation of spermine in EXOD-1 cells were not significantly altered by the mutant antizyme, whereas wild-type antizyme decreased spermine transport and accumulation. When the peptide 69-118, which is responsible for the degradation of ODC, was deleted from antizyme, the mutant antizyme showed a smaller effect compared with the normal antizyme in terms of the inhibition of spermine transport and the recovery from the spermine inhibition of cell growth. The results indicate that regions 119-144 and 211-216 in antizyme are necessary for the negative regulation of polyamine transport and that these regions overlap with ODC binding sites.

N1-dansyl-spermine and N1-(n-octanesulfonyl)-spermine, novel glutamate receptor antagonists: block and permeation of N-methyl-D-aspartate receptors

The effects of several N-sulfonyl-polyamines, including N1-dansyl-spermine (N1-DnsSpm) and N1-(n-octanesulfonyl)-spermine (N1-OsSpm), were studied at recombinant N-methyl-D-aspartate (NMDA) receptors expressed in Xenopus laevis oocytes. N1-DnsSpm and N1-OsSpm inhibited NMDA receptors and were approximately 1000-fold more potent than spermine in oocytes voltage-clamped at -70 mV. Block by N1-DnsSpm and N1-OsSpm was strongly voltage dependent, being more pronounced at hyperpolarized membrane potentials. With the Woodhull model of voltage-dependent channel block, the values of Kd(0) were 779 microM, 882 microM, and 7.4 mM and those of z delta were 2.58, 2.57, and 1.07 for N1-DnsSpm, N1-OsSpm, and spermine, respectively. This suggests that an increase in the voltage dependence of block together with an increase in affinity contributes to the increased potencies of N1-DnsSpm and N1-OsSpm compared with spermine. Sensitivity to N1-DnsSpm was reduced by mutation NR1(N616Q) and was increased by mutations NR1(N616G) and NR2A(N615G). The NR1(N616G) and NR2A(N615G) mutations decreased the Kd(0) value of N1-DnsSpm without affecting z delta, whereas the NR1(N616Q) mutation reduced z delta. These mutations may alter the accessibility of part of the polyamine binding site within the channel pore or directly alter the properties of that site. Block by N1-DnsSpm (0.3 microM) was almost complete at -100 mV, and there was no relief of block at extreme negative membrane potentials (-100 to -200 mV) at wild-type NR1/NR2A channels. In contrast, block by N1-DnsSpm was partially relieved at extreme negative potentials at receptors containing NR1(N616G) or NR2A(N615G), suggesting that N1-DnsSpm can permeate these mutant channels but not wild-type NR1/NR2A channels. This is hypothesized to be due to an increase in the pore size of channels containing NR1(N616G) or NR2A(N615G), which allows passage of the bulky head group of N1-DnsSpm. In contrast to N1-DnsSpm, N1-OsSpm could easily permeate wild-type NR1/NR2A channels, presumably because the head group of N1-OsSpm can pass through the narrowest part of the channel pore. N-Sulfonyl-polyamines such as N1-DnsSpm and N1-OsSpm represent a new class of polyamine antagonists with which to study glutamate receptor ion channels.

Excretion and uptake of putrescine by the PotE protein in Escherichia coli

The structure and function of the polyamine transport protein PotE was studied. Uptake of putrescine by PotE was dependent on the membrane potential. In contrast, the putrescine-ornithine antiporter activity of PotE studied with inside-out membrane vesicles was not dependent on the membrane potential (Kashiwagi, K., Miyamoto, S., Suzuki, F., Kobayashi, H., and Igarashi, K. (1992) Proc. Natl. Acad. Sci. U. S. A. 89, 4529-4533). The Km values for putrescine uptake and for putrescine-ornithine antiporter activity were 1.8 and 73 microM, respectively. Uptake of putrescine was inhibited by high concentrations of ornithine. This effect of ornithine appears to be due to putrescine-ornithine antiporter activity because it occurs only after accumulation of putrescine within cells and because ornithine causes excretion of putrescine. Thus, PotE can function not only as a putrescine-ornithine antiporter to excrete putrescine but also as a putrescine uptake protein. Both the NH2 and COOH termini of PotE were located in the cytoplasm, as determined by the activation of alkaline phosphatase and beta-galactosidase by various PotE-fusion proteins. The activities of putrescine uptake and excretion were studied using mutated PotE proteins. It was found that glutamic acid 207 was essential for both the uptake and excretion of putrescine by the PotE protein and that glutamic acids 77 and 433 were also involved in both activities. These three glutamic acids are located on the cytoplasmic side of PotE, and the function of these three residues could not be replaced by other amino acids. Putrescine transport activities did not change significantly with mutations at the other 13 glutamic acid or aspartic acid residues in PotE.

Molecular mechanism of polyamine stimulation of the synthesis of oligopeptide-binding protein

Polyamine stimulation of the synthesis of oligopeptide-binding protein (OppA) was shown to occur mainly at the level of translation by measuring OppA synthesis and its mRNA level. Several artificial oppA genes were constructed by site-directed mutagenesis. These synthesize different kinds of OppA mRNAs: mRNAs differing in the size of 5'-untranslated region; mRNAs having the Shine-Dalgarno (SD) sequence in a different position; mRNAs having different secondary structure in the region of the SD sequence; and fusion mRNAs consisting of the 5'-untranslated region of OppA mRNA and the open reading frame of beta-galactosidase. By measuring the synthesis of OppA or beta-galactosidase from these mRNAs, we found that the 171-nucleotide 5'-untranslated region and 145 nucleotides of the ORF of OppA mRNA are involved in the polyamine stimulation of OppA synthesis. When the secondary structure of the above region of OppA mRNA was analyzed by optimal computer folding, it was shown that the degree of polyamine stimulation of OppA protein synthesis was dependent on the structure of the SD sequence in addition to its position. Loose base pairing of the SD sequence with other regions of the mRNA caused strong polyamine stimulation, while intense base pairing of the SD sequence with other regions of the mRNA resulted in insignificant or weak polyamine stimulation.

Calponin distribution in human ciliary muscle and other anterior segment tissues

PURPOSE

Calponins are a family of actin-binding proteins known to regulate aortic and tracheal smooth muscle contraction. This investigation was undertaken to assess the presence, subtype, and distribution of calponin proteins in human ciliary muscle, iris, and other anterior segment tissues as well as expression in ciliary muscle cells in vitro.

METHODS

The distribution of calponin immunoreactivity was assessed in paraffin sections of human anterior segment tissue. Human ciliary muscle proteins were analyzed by polyacrylamide gel electrophoresis and Western blotting. The regulation of calponin expression was compared with alpha-sm-actin expression in preconfluent and postconfluent ciliary muscle cell cultures by immunocytochemistry. To determine total cell counts, the cultures were counter-stained with ethidium homodimer. As control specimens, expression of calponin and alpha-sm-actin also was assessed in human Tenon fibroblast cultures.

RESULTS

Strong calponin immunoreactivity was present in ciliary muscle, iris dilator and sphincter muscles, and blood vessel smooth muscle. Fine immunostained strands also were observed in the scleral spur. This distribution was similar to alpha-sm-actin. Western blotting showed a single band of calponin with a molecular weight of 32 kDa. In the cultured ciliary muscle cells, calponin stained straight cable-like fibers running parallel along the long axis of the cells. Although the proportion of calponin immunoreactive cells was reduced substantially in preconfluent cultures, virtually all cells were stained in confluent primary through fourth-passage cultures. Cultured human Tenon fibroblasts did not show either calponin or alpha-sm-actin immunoreactivity.

CONCLUSIONS

Calponin is expressed in human ciliary muscle, iris smooth muscles, blood vessel smooth muscle, as well as within the scleral spur. In addition, calponin is expressed by ciliary smooth muscle cells in vitro. The role of calponin in contraction of these tissues should be investigated.

Prostaglandin action on ciliary smooth muscle extracellular matrix metabolism: implications for uveoscleral outflow

The cellular mechanisms mediating intraocular pressure reduction following topical prostaglandin (PG) treatments are poorly understood. To determine if PG treatments might induce altered metabolism of extracellular matrix surrounding ciliary muscle cells, confluent human ciliary smooth muscle cell cultures were exposed to PGF 2 alpha' 17-phenyltrinor-PGF2 alpha' or 11-deoxy-PGE1 for one to four days and the distributions of collagen types I, III and IV as well as laminin were determined immunocytochemically. In addition, collagen type IV and promatrix metalloproteinase III (proMMP-3) content within treated cultures was determined using sandwich ELISAs. Compared with vehicle-treated cultures, there were substantial reductions in the density and branching of the collagen type IV-immunoreactive lattice accompanied by thickening of remaining strands in all PG-treated cultures. Similar changes were seen in the distribution of laminin within all PG-treated cultures. Reductions in collagen type III immunoreactivity were seen in cultures treated with either PGF2 alpha or 17-phenyltrinor-PGF2 alpha. No changes were observed in collagen type I immunoreactivity. Quantitative analyses revealed increased amounts of collagen type IV in both the culture medium and in extracts of the cell layer in all PG-treated cultures. In addition, there were substantial increases in the concentrations of proMMP-3 in all PG-treated cultures. These results indicate that PGs induce increased turnover and remodeling of ECM adjacent to ciliary muscle cells. Such changes may contribute to increased uveoscleral outflow in vivo following topical PG treatment.

A method to extract three-dimensional objects from three-dimensional NMR image data

A method to extract shapes of bubble polyhedra from three-dimensional nuclear magnetic resonance image data of foam has been developed. The method consists of four steps: first, to compute series of maximum intensity projection images from the three-dimensional NMR image data of foam to visualize the network structure of the bubble edges; second, to measure the three-dimensional coordinates of vertices of the bubble polyhedra interactively on a CRT using the series of MIP images to obtain polyhedral edges; third, to construct polyhedral faces from the assembly of the edge data; and fourth, to construct bubble polyhedra from the assembly of the face data. The algorithm for construction of polygons and polyhedra is based on the selection of polygons or polyhedra from an enormous number of possible combinations of edges or faces under some simple selection rules. Since the computation time for the selection increased exponentially with the number of the edge data, a 'partial volume sweeping' method in which a cubic region which could accommodate any bubble polyhedron was swept over the three-dimensional image area, was developed to reduce the computation time. By using this method, it was demonstrated that the shapes of many bubble polyhedra could be extracted automatically from the assembly of the edge data within a practical computation time.

The 1.8-A X-ray structure of the Escherichia coli PotD protein complexed with spermidine and the mechanism of polyamine binding

The PotD protein from Escherichia coli is one of the components of the polyamine transport system present in the periplasm. This component specifically binds either spermidine or putrescine. The crystal structure of the E. coli PotD protein complexed with spermidine was solved at 1.8 A resolution and revealed the detailed substrate-binding mechanism. The structure provided the detailed conformation of the bound spermidine. Furthermore, a water molecule was clearly identified in the binding site lying between the amino-terminal domain and carboxyl-terminal domain. Through this water molecule, the bound spermidine molecule forms two hydrogen bonds with Thr 35 and Ser 211. Another periplasmic component of polyamine transport, the PotF protein, exhibits 35% sequence identity with the PotD protein, and it binds only putrescine, not spermidine. To understand these different substrate specificities, model building of the PotF protein was performed on the basis of the PotD crystal structure. The hypothetical structure suggests that the side chain of Lys 349 in PotF inhibits spermidine binding because of the repulsive forces between its positive charge and spermidine. On the other hand, putrescine could be accommodated into the binding site without any steric hindrance because its molecular size is much smaller than that of spermidine, and the positively charged amino group is relatively distant from Lys 349.

Activation of N-methyl-D-aspartate receptors by glycine: role of an aspartate residue in the M3-M4 loop of the NR1 subunit

Glutamate and glycine are coagonists that act at distinct sites to activate N-methyl-D-aspartate (NMDA) receptors. In the NR1 subunit of the NMDA receptor, mutation of D732 to glutamate (D732E), asparagine (D732N), alanine (D732A), or glycine (D732G) reduced the potency of glycine by > 4000-fold, but these mutations had no effect on sensitivity to glutamate. Mutations at NR1(D732) also changed sensitivity to the glycine-site agonists D-serine and D-alanine, reducing the potencies and, in some cases, the efficacies of these compounds. Thus, D-serine was a full agonist at the glycine site of receptors containing NR1(D732N) and NR1(D732A), a partial agonist at receptors containing NR1(D732G), and a competitive antagonist at receptors containing NR1(D732). Mutations at NR1(D732) had no effect or produced an increase in sensitivity to the glycine-site antagonists 6,7-dichloroquinoxaline-2,3-dione and 5,7-dichlorokynurenic acid. These mutations did not affect the reversal potential, voltage-dependent block by extracellular Mg2+, block by ifenprodil, or stimulation by spermine at NR1/NR2B receptors. NR2 subunits containing mutations at NR2A(D731) and NR2B(D732), which correspond to NR1(D732), did not produce functional receptors when coexpressed with NR1. Residue D732 in NR1 may be close to a glycine binding site on the NMDA receptor and may directly affect the properties of this site or be critical for coupling of glycine binding to channel activation.

Prostaglandins increase proMMP-1 and proMMP-3 secretion by human ciliary smooth muscle cells

PURPOSE

The mechanism by which prostaglandin(PG)F2 alpha increases uveoscleral outflow and lowers intraocular pressure in primates is not known. In cultured human ciliary muscle cells, PGF2 alpha induces the expression of the protooncogene c-fos which is known to induce the transcription of genes such as matrix metalloproteinase-1 (MMP-1) and MMP-3 in other cell systems. As these enzymes are initially secreted as proenzymes, the present study was undertaken to determine if PG treatment induces ciliary muscle cells to secrete either proMMP-1 or proMMP-3.

METHODS

Human ciliary smooth muscle cells were grown to confluence in monolayer cell cultures and then treated with PGF2 alpha, 17-phenyltrinor-PGF2 alpha, or 11-deoxy-PGE1. Medium harvested at various times after treatment was assayed for proMMP-1 and proMMP-3 content using sandwich ELISAs.

RESULTS

Three days after adding 10 nM PGF2 alpha, proMMP-1 and proMMP-3, concentrations in the culture medium were increased by 254 +/- 33% (mean +/- SE) and 128 +/- 13%, respectively. Compared with vehicle controls, 24 h treatment with 200 nM PGF2 alpha, 17-phenyltrinor-PGF2 alpha, or PGE1, increased proMMP-1 by 116 +/- 29%, 169 +/- 26%, and 273 +/- 16%, respectively. In parallel experiments, proMMP-3 was increased by 99 +/- 18%, 82 +/- 24%, and 214 +/- 16%, respectively.

CONCLUSIONS

These results suggest that induction of MMPs in situ following topical PG treatment may degrade ciliary muscle extracellular matrix and possibly contribute to increased uveoscleral outflow, as well.

Maternal and zygotic expression of mRNA for S-adenosylmethionine decarboxylase and its relevance to the unique polyamine composition in Xenopus oocytes and embryos

From Xenopus tailbud cDNA library, we isolated the cDNA for S-adenosylmethionine decarboxylase (SAMDC), an enzyme which provides putrescine and spermidine with the aminopropyl group to form spermidine and spermine, respectively. The cDNA coded for 335 amino acids whose sequence had high homology (ca. 83%) to other vertebrate SAMDCs, preserving the sequences reportedly essential for enzyme activity, proenzyme processing, and putrescine stimulation of the enzyme activity. Northern blot analysis showed one major mRNA signal of ca. 3.5 kb, with a minor signal of ca 2.0 kb which may probably be due to cross-hybridization. In oocytes the SAMDC mRNA occurred from stage I, and its amount peaked at stage II, then gradually decreased from stage III to VI. The decreased level of the mRNA was maintained during oocyte maturation, further decreased from the cleavage to early neurula stage, and then increased greatly due to the zygotic expression during late neurula stages (stage 21-25), reaching a plateau level at the late tailbud stage (stage 28). Enzyme assays showed that the changing level of the SAMDC mRNA was reflected in the level of the functional enzyme, suggesting strongly that the zygotic expression of the mRNA leads to a large increase in the amount of SAMDC, albeit in the pre-neurula embryo the amount of the enzyme is very small. We found that the relative composition of polyamines is the eukaryote-type (high-level spermine) at the beginning of oogenesis, but it changes to the prokaryote-type, or more appropriately Escherichia coli-type (high-level putrescine but background level spermine) during oocyte maturation, and remains E. coli-type throughout embryogenesis. We assume that the E. coli-type polyamine composition is a necessary factor for the normal embryogenic development in Xenopus and its maintenance, especially that in pre-neurula stages, can be explained by the low level of both SAMDC mRNA and SAMDC.

Spermidine regulation of protein synthesis at the level of initiation complex formation of Met-tRNAi, mRNA and ribosomes

Spermidine regulation of protein synthesis (stimulation at low concentrations and inhibition at high concentrations) was studied using a mRNA with a GC-rich 5'-untranslated region. It was found that the initiation complex formation of mRNA, Met-tRNAi, and 40 S ribosomal subunits was regulated by spermidine. The inhibition of initiation complex formation at high spermidine concentrations was greater with 80 S ribosomes than with 40S ribosomal subunits. This was partially explained by the spermidine inhibition of initiation factor-dependent RNA helicase activity.

An aspartate residue in the extracellular loop of the N-methyl-D-aspartate receptor controls sensitivity to spermine and protons

To study the role of acidic residues in modulation of NMDA receptors by spermine, we used site-directed mutagenesis of receptor subunits and voltage-clamp recording in Xenopus oocytes. Sixteen glutamate and aspartate residues, located in the first two thirds of the putative extracellular loop of the NR1A subunit, were individually mutated. This region of NR1A shows homology with bacterial amino acid binding proteins, a bacterial polyamine binding protein, and a bacterial spermidine acetyltransferase. Mutation of D669 to asparagine (D669N), alanine (D669A), or glutamate (D669E) abolished the "glycine-independent" form of spermine stimulation in heteromeric NR1A/NR2B receptors. These mutations also markedly reduced inhibition by ifenprodil and by protons at NR1A/NR2B receptors. Mutations at the equivalent position (D690) in NR1B, which contains the insert encoded by exon 5, reduced the pH sensitivity of NR1B/NR2B receptors. Thus, the effects of mutations at D669 are not prevented by the presence of exon 5, and the influence of exon 5 is not prevented by mutations at D669 (D690 in NR1B). Mutations at NR1A (D669) had little or no effect on the potencies of glutamate and glycine and did not alter voltage-dependent block by Mg2+ or the "glycine-dependent" form of spermine stimulation. Surprisingly, the D669N and D669A mutations, but not the D669E mutation, reduced voltage-dependent block by spermine at NR1A/NR2 receptors. Mutations in NR2B at a position (D668) equivalent to D669 did not alter spermine stimulation or sensitivity to pH and ifenprodil. However, mutations D668N and D668A but not D668E in NR2B reduced voltage-dependent block by spermine. Screening of the negative charges at NR1A(D669) and NR2B(D668) may be involved in voltage-dependent block by spermine. D669 in NR1A could form part of a binding site for polyamines and ifenprodil and/or part of the proton sensor of the NMDA receptor. Alternatively, this residue may be critical for coupling of modulators such as spermine, protons, and ifenprodil to channel gating.