A general additive distance with time-reversibility and rate variation among nucleotide sites

As additivity is a very useful property for a distance measure, a general additive distance is proposed under the stationary time-reversible (SR) model of nucleotide substitution or, more generally, under the stationary, time-reversible, and rate variable (SRV) model, which allows rate variation among nucleotide sites. A method for estimating the mean distance and the sampling variance is developed. In addition, a method is developed for estimating the variance-covariance matrix of distances, which is useful for the statistical test of phylogenies and molecular clocks. Computer simulation shows (i) if the sequences are longer than, say, 1000 bp, the SR method is preferable to simpler methods; (ii) the SR method is robust against deviations from time-reversibility; (iii) when the rate varies among sites, the SRV method is much better than the SR method because the distance is seriously underestimated by the SR method; and (iv) our method for estimating the sampling variance is accurate for sequences longer than 500 bp. Finally, a test is constructed for testing whether DNA evolution follows a general Markovian model.

[Radiation therapy of esophageal carcinoma: a report on 180 cases]

One hundred eighty patients with pathologically proved esophageal carcinoma accepted for surgery, for various resons, were given radical radiation therapy. The length of the lesions ranged from 2 to 9 cm. They were treated either by the isocenter technique alone or A-P plus isocenter irradiation to a total dose of 50-70 Gy/5-7 wk. The 1-, 3- and 5-year survival rate was 64.4%, 34.4% and 23.3%, respectively. The 3- and 5-year survival rates showed that lesions in the upper third responded to radiotherapy better than did those in the middle and lower thirds (P < 0.05). The 5-year survival of patients with upper third lesions treated with radiation alone (44.5%) was slightly better than that of surgery. The result of lesions in the middle third was slightly inferior, and that of lower third was even more inferior to that of surgery. The result of radiation alone for operable esophageal carcinoma was comparable to that of surgery.

Spectrophotometric method for the determination of ascorbic acid with iron (III)-1,10-phenanthroline after preconcentration on an organic solvent-soluble membrane filter

A solvent-soluble membrane filter is proposed for the simple and rapid preconcentration and spectrophotometric determination of ascorbic acid based on the reduction of 1, 10-phenanthroline (phen)-iron (III), which is collected on a nitrocellulose membrane filter as an ion-associate of the cationic complex of tri,phen-iron (II) [ferroin, Fe(phen)(2+)(3)] with an anionic surfactant (of dodecyl sulfate). The ion-associate collected is dissolved in a small volume of 2-methoxyethanol together with the filter. The colour intensity is measured at 510 nm against the reagent blank and is proportional to the content of ascorbic acid in the range 2.5-50 microg ascorbic acid in 5 ml of solvent with excellent reproducibility (RSD 3.2% for 200 microg 1(-1) ascorbic acid), the enrichment factor achieves 100-fold and detection limits better than 2.0 microg 1(-1) can be obtained. Diverse components of organic and inorganic compounds normally present in fruits, vegetable, beverages and urine do not interfere. The recoveries of the ascorbic acid added to the samples are quantitative.

Rapid monitoring of site-specific glycosylation microheterogeneity of recombinant human interferon-gamma

An analytical system is presented for rapid assessment of site-specific microheterogeneity of the two potential N-linked glycosylation sites of recombinant human interferon-gamma (IFN-gamma) derived from Chinese hamster ovary cell culture. The target protein is first purified from culture supernatant by immunoaffinity chromatography, and the acidic eluent is neutralized via an in-line mixing tee. On-line proteolysis is rapidly performed by an immobilized trypsin cartridge, and reversed-phase chromatography isolates the two pools of glycopeptides representing the potential glycosylation sites. Following off-line analysis by matrix-assisted laser-desorption ionization/time-of-flight (MALDI/TOF) mass spectrometry, observed mass shifts of glycopeptides relative to the known masses of their amino acid portions are correlated to site-specific oligosaccharide structures. Desialylation of glycopeptides by sialidase treatment on the MALDI sample plate allows for quantitative estimations of asialoglycan structures by MALDI/TOF. This methodology permits glycoprotein microheterogeneity to be evaluated in a time frame of approximately 2 h, utilizing as little as 0.5 microgram (25 pmol) of product. Results of monitoring a batch culture are presented as well as analysis of a culture containing deoxymannojirimycin, an inhibitor of glycoprotein processing.

Interaction of tRNA (uracil-5-)-methyltransferase with NO2Ura-tRNA

tRNA in which uracil is completely replaced by 5-nitro-uracil was prepared by substituting 5-nitro-UTP for UTP in an in vitro transcription reaction. The rationale was that the 5-nitro substituent activates the 6-carbon of the Ura heterocycle towards nucleophiles, and hence could provide mechanism-based inhibitors of enzymes which utilize this feature in their catalytic mechanism. When assayed shortly after mixing, the tRNA analog, NO2Ura-tRNA, is a potent competitive inhibitor of tRNA-Ura methyl transferase (RUMT). Upon incubation, the analog causes a time-dependent inactivation of RUMT which could be reversed by dilution into a large excess of tRNA substrate. Covalent RUMT-NO2Ura-tRNA complexes could be isolated on nitrocellulose filters or by SDS-PAGE. The interaction of RUMT and NO2Ura-tRNA was deduced to involve formation of a reversible complex, followed by formation of a reversible covalent complex in which Cys 324 of RUMT is linked to the 6-position of NO2Ura 54 in NO2Ura-tRNA.

Phragmoplastin, a dynamin-like protein associated with cell plate formation in plants

Cytokinesis in a plant cell is accomplished by the formation of a cell plate in the center of the phragmoplast. Little is known of the molecular events associated with this process. In this study, we report the identification of a dynamin-like protein from soybean and demonstrate that this protein is associated with the formation of the cell plate. Plant dynamin-like (PDL) protein contains 610 amino acids showing high homology with other members of the dynamin protein family. Western blot experiments demonstrated that it is associated with the non-ionic detergent-resistant fraction of membranes. Indirect immunofluorescence microscopy localized PDL to the cell plate in dividing soybean root tip cells. Double labeling experiments demonstrated that, unlike phragmoplast microtubules which are concentrated on the periphery of the forming plate, PDL is located across the whole width of the newly formed cell plate. Based on the temporal and spatial organization of PDL in the phragmoplast, we termed this protein 'phragmoplastin'. The data suggest that phragmoplastin may be associated with exocytic vesicles that are depositing cell plate material during cytokinesis in the plant cell.

Early enhancement but no late changes of motor responses induced by intracortical microstimulation in the ketamine-anesthetized rat

The objectives of this study were to determine whether changes in electromyographic (EMG) responses observed during prolonged intracortical microstimulation (ICMS) were due to local plasticity of the motor system or to global changes in the preparation. Local effects would be expressed as changes only along the activated motor pathway, whereas global effects would be expressed as changes also appearing at distant cortical efferent microzones. The results of ICMS in the ketamine-anesthetized rat showed that the size of consecutive EMG responses increased gradually to a relatively stable magnitude over a period of four to six trains of stimuli. This early enhancement of EMG responses was maintained while continuously providing trains of stimuli at 1 Hz. However, it disappeared after a 5-min period of muscle inactivity. This response enhancement in the presence of ketamine (an NMDA, N-methyl-D-aspartate, receptor blocker) suggests that a neuronal mechanism involving non-NMDA-mediated homosynaptic short-term potentiation (STP) was responsible for the early enhancement of EMG responses. To compare ICMS effects at several time intervals it was necessary to average several evoked EMG responses because there was normal biological variability between single EMG responses. To determine the optimal number of EMG responses that would provide a reliable average EMG response, averages of 5, 10, 15, 20, and 25 EMG responses evoked from a single cortical site were collected at 5-min intervals. The results revealed that averages of 10 responses would provide reliable average EMG responses for all subsequent analyses. There were wide fluctuations in the average EMG responses when periodic injections of ketamine were used to maintain a low reflexive state in the animal. Switching to continuous infusion of ketamine abolished these fluctuations but there remained a small drift in the magnitudes of consecutive EMG responses. To test whether this drift reflected local plastic changes in the motor system induced by stimulation or some global changes, EMG responses evoked from another ICMS site were used as control. The rationale was that global effects would affect all motor output sites equally. The sizes of control EMG responses followed a similar time course to those evoked from the test site. Furthermore, standardizing the test EMG responses with respect to the control responses eliminated the drift in response magnitudes. Thus the drift was due to slow global changes in neuronal excitability possibly produced by the anesthesia. In conclusion, late changes occurring after hours of ICMS were not due to plasticity of the motor system but rather to global changes in the preparation, possibly resulting from the inability to set an ideal anesthetic infusion rate that could maintain a constant level of neuronal excitability over long periods of time. However, there was early enhancement of the EMG responses evoked by ICMS due to neuronal plasticity possibly mediated by a non-NMDA mechanism of homosynaptic STP such as post-tetanic potentiation (PTP). This early enhancement would favor recruitment of the previously activated motor pathway and lead to greater consistency in movement execution.

The crystal structure of a high oxygen affinity species of haemoglobin (bar-headed goose haemoglobin in the oxy form)

We have determined the crystal structure of bar-headed goose haemoglobin in the oxy form to a resolution of 2.0 A. The R-factor of the model is 19.8%. The structure is similar to human HbA, but contacts between the subunits show slightly altered packing of the tetramer. Bar-headed goose blood shows a greatly elevated oxygen affinity compared to closely related species of geese. This is apparently due to a single proline to alanine mutation at the alpha 1 beta 1 interface which destabilises the T state of the protein. The beta chain N and C termini are well-localized, and together with other neighbouring basic groups they form a strongly positively charged groove at the entrance to the central cavity around the molecular dyad. The well-ordered conformation and the three-dimensional distribution of positive charges clearly indicate this area to be the inositol pentaphosphate binding site of bird haemoglobins.

Isolation of the C9b fragment of human complement component C9 using urea in the absence of detergents

The bactericidal activity of the C5b-9 complex of complement is dependent upon the terminal complement component C9. The precursor C5b-8 complex is not harmful to bacterial cells until C9 is added to complete the C5b-9 complex. The C9 molecule can be proteolytically cleaved by thrombin to yield an intact, nicked molecule that remains fully functional when added to either bacterial cells or erythrocytes bearing pre-formed C5b-8 complexes. In investigating the membranolytic function of C9 in the C5b-9 complex, the carboxyl-terminal portion of the nicked molecule (C9b) has been shown to be membranolytic when added to erythrocytes, liposomes, or bacterial inner membranes in the absence of any other complement components. The isolation of C9b from nicked C9 has been accomplished by preparative gel electrophoresis using detergents, however the study of the activity of C9b in membrane systems may be complicated by the possible presence of residual detergent. To address this concern, we have used 4 M urea in conjunction with hydroxyapatite chromatography and a phosphate elution procedure to separate the domains of nicked C9. The isolated C9b domain, free of detergents and in the absence of any other complement components, was found to be membranolytic. C9b isolated in this manner was capable of lysing erythrocytes and inhibiting the growth of bacterial spheroplasts.

Posttranslational regulation of type I collagen in corneal endothelial cells

PURPOSE

Type I collagen synthesis in corneal endothelial cells does not correlate with steady state collagen RNA levels; although substantial amounts of alpha 2(I) collagen RNA are present in these cells, type I collagen is not detected. This allowed the authors to investigate the possibility of posttranscriptional control of type I collagen in corneal endothelial cells.

METHODS

The alpha 2(I) collagen RNA structures of normal and modulated corneal endothelial cells were analyzed by S1 nuclease protection analysis, whereas the nucleotide sequences were obtained by rapid amplification of cDNA ends technique. In situ hybridization of type I collagen was demonstrated with immunofluorescence; synthesis and degradation of the molecule were analyzed by pulse-chase experiments and then by immunoprecipitation with antiprocollagen I antibody.

RESULTS

The cDNA covering the 5'-untranslated region (UTR) of alpha 2(I) collagen RNA obtained from normal corneal endothelial cells and from modulated corneal endothelial cells that predominantly produce type I collagen demonstrate identical sequences in their 5' untranslated and coding sequences. In both mRNA, the length of the 5'-untranslated segment is 127 nucleotides. There were also two AUG codons; the second AUG codon, which is 17 nucleotides upstream from the translation initiation codon, is conserved, as observed in human and chicken alpha 2(I) mRNA. When the sequence covering the 3'-UTR of corneal endothelial alpha 2(I) mRNA was compared with that of alpha 2(I) mRNA obtained from the modulated cells, there were differences in only two nucleotides. The length of the 3'-untranslated segment of each mRNA is 297 nucleotides up to the consensus polyadenylation recognition site (AAUAAAAUAAA), which both cells use. Immunofluorescent staining of corneal tissue in vivo demonstrated that the corneal endothelium stains with anti-type I collagen antibodies, but there is no staining in the underlying Descemet's membrane. In pulse-chase experiments, the newly synthesized type I procollagen, composed of pro alpha 1(I) and pro alpha 2(I) chains as determined by V8 protease peptide mapping, reached the highest intracellular level at 45 minutes, after which its detection decreased. Cells chased for 120 minutes demonstrated no trace of type I procollagen in the cell layer; medium fractions showed no detectable type I procollagen during the entire 120-minute chase.

CONCLUSIONS

These results suggest that type I collagen is synthesized in corneal endothelial cells and that such undesired expression is regulated at the posttranslational level, perhaps by intracellular degradation.

Micellar electrokinetic capillary chromatography combined with immunoaffinity chromatography for identification and determination of dexamethasone and flumethasone in equine urine

A capillary electrophoresis technique was developed for the separation of synthetic glucocorticoids and the determination of dexamethasone and flumethasone in horse urine. Pretreatment of the sample using a dexamethasone affinity column resulted in low background that enabled the authors to detect levels as low as 1.1 ng/mL and 2.7 ng/mL for dexamethasone and flumethasone in horse urine, respectively. The developed method was used to detect dexamethasone in horse urine samples after the injection of a therapeutic dose of dexamethasone for up to 12 hr postinjection. The optimum conditions for capillary electrophoresis and dexamethasone elution from the affinity column are described.

A rapid method for detecting and mapping in vitro transcripts from supercoiled templates using endogenous RNase H

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Signalling pathways in cardiac failure

1. Cardiac failure in humans and in animal models is associated with a marked desensitization of the catecholamine signalling pathway. 2. Beta 1- and beta 2- and possibly beta 3-adrenoceptors (beta-AR) are found in the hearts of humans and common laboratory animals such as rats and guinea-pigs. In rats and guinea-pigs chronic stimulation of cardiac beta-AR leads to a rapid loss of beta 2-AR whereas heart failure in humans is associated with a loss of beta 1-AR or beta 1-AR and beta 2-AR. 3. Desensitization is also associated with phosphorylation of beta-AR by beta-AR kinase (beta-ARK) and uncoupling of receptors from the signalling pathway. Beta-ARK but not beta-arrestin activity and mRNA are markedly increased in heart failure. 4. Chronic beta-AR stimulation and heart failure are associated with increases in Gi alpha but little if any change in Gs alpha. 5. The roles of beta gamma subunits of G-proteins, adenylate cyclase subtypes and cAMP dependent protein kinase A in heart failure are unclear at present.

ABBREVIATIONS

beta-ARK - beta-adrenoceptor kinase AR - adrenoceptor G-protein - GTP binding protein

Determination of tetracycline residues in bovine milk, serum, and urine by capillary electrophoresis

A method was developed for simultaneous determination of oxytetracycline (OTC), chlortetracycline, tetracycline, and doxycycline levels in cow milk, serum, and urine by capillary electrophoresis (CE). The tetracyclines (TCs) were extracted specifically with a metal-chelating affinity column. Extracts were then applied to C18 cartridges treated with dimethyldichlorosilane, and the TCs were eluted with ethanol. Salt-free sample residues were run on CE with a diode array detector at 370 nm. A 50 cm x 75 micron uncoated capillary at 15 kV and 23 degrees C was used to separate the TCs. The run buffer contained 10 mM sodium dodecyl sulfate, 50 mM borate, and 50 mM phosphate, pH 8.5. TC peaks were identified by migration times, coinjection of standards, and diode array spectra. Limits of detection for TCs were 1.3-5.6 ng/mL, and limits of quantitation were 1.7-8.7 ng/mL in cow fluid samples. OTC appeared consistently at 13.3-13.4 min in milk, serum, and urine samples from a cow treated with OTC. OTC was further identified by coinjection of OTC standard and OTC diode array spectra. The CE method can be used to simultaneously determine 4 TC residues at low parts-per-billion levels.

Proton nuclear magnetic resonance studies on huwentoxin-I from the venom of the spider Selenocosmia huwena: 1. Sequence-specific 1H-NMR assignments

The complete sequence-specific assignments of resonances in the 1H-NMR spectrum of huwentoxin-I from the Chinese bird spider, Selencocosmia huwena, is described. A combination of two-dimensional NMR experiments including 2D-COSY, 2D-NOESY, and 2D-TOCSY has been employed on samples of the toxin dissolved in D2O and in H2O for assignment purposes. Protons belonging to spin systems for each of the 33 amino acids were identified. The sequence-specific assignments were facilitated by the identification of d alpha N connectivities on the fingerprint regions of the COSY and NOESY spectra and were supported by the identification of dNN and d alpha N connectivities in the TOCSY and NOESY spectra. These studies provide a basis for the determination of the solution-phase conformation of this toxin.

Producing columnar depositions of neuroanatomical tracer in rat cortex

A new technique was developed to fill columnar regions of cortex with retrograde neuroanatomical tracer. This technique involved (1) standard iontophoresis to eject tracer from a micropipette in concert with (2) displacement of this micropipette radially through the cortex using a computer controlled microdrive. The displacement of the micropipette left an evenly dense deposit of tracer throughout the cortical thickness forming a column of neuroanatomical tracer. The diameter of the columnar injection site was reliably dependent on the iontophoretic current strength, the micropipette displacement parameters, and the nature of the tracer used. This simple technique provided very reproducible results. Several issues related to the interconnections of functionally identified columns of sensory and motor cortex could be addressed with this injection technique.

Effect of pH on potassium and proton conductance in renal proximal tubule

The effect of intracellular and extracellular pH on potassium conductance (GK) was examined in isolated amphibian (Rana pipiens) proximal tubule cells under whole cell voltage clamp conditions. Internal perfusion of the patch pipette was used to precisely control intracellular pH. In the region of normal resting potential (-51 +/- 3 mV), raising cell pH from 6.5 to 8.0 did not significantly increase GK (1.1 +/- 0.3 vs. 1.3 +/- 0.3 nS; P > 0.08, n = 8). Similar elevations in external (bath) pH had even less of an effect on GK. In contrast, when cells were voltage clamped to 30 mV more negative than the resting potential, raising internal pH from 6.5 to 8.0 did increase GK from 1.05 +/- 0.3 to 1.8 +/- 0.5 nS (P < 0.04; n = 8). These results suggest that modest changes in pH have little effect on GK, except at large negative potentials. In the process of examining the pH dependence of GK, a slowly activating, voltage-dependent conductance of 7.5 +/- 1 nS (n = 20; for 20 microns cells) was observed during cell depolarization. Although the instantaneous current-voltage relation of this conductance was linear, its marked voltage dependence produced an apparent steady-state rectification, with Gm = 0.5 +/- 0.2 nS and Gout = 9.0 +/- 1 nS (n = 11). Outward current was reversibly blocked by 3 mM Cu, Cd, or Co. In the absence of Na, K, and Ca (and only trace amounts of Cl), rapid changes in bath pH from 6.5 to 8.0 shifted the steady-state reversal potential (Erev) by -37 +/- 4 mV (n = 9) and the instantaneous Erev by -56 +/- 4 mV (n = 9). These shifts in Erev were consistent with a hydrogen ion conductance (GH), similar to what has been reported for snail neuron, neutrophils, alveolar epithelial cells, and phagocytes. Since the magnitude of this GH would be insignificant at resting cell pH and membrane potential, its role in renal proximal tubule under normal conditions is somewhat obscure. Nonetheless, in pathological situations, GH could function to prevent acid overload during any process that depolarizes the cell, such as low temperature or metabolic inhibition.

Insulin-like growth factor-I promotes cell proliferation in the absence of modulation of collagen phenotypes and utilizes IRS-1, not PLC-gamma 1, in corneal endothelial cells

Corneal endothelial cells are differentiated cells and are thus incapable of physiologic regeneration. In a search for a growth factor that would promote optimal proliferation of corneal endothelial cells in the absence of other modulating activities, the effect of insulin-like growth factor-I (IGF-I) on rabbit corneal endothelial cells was studied. In addition, cellular effector molecules responsible for the signal pathway for IGF-I were studied. IGF-I at 50 ng/ml stimulated corneal endothelial cell proliferation after at least 8 h of treatment. IGF-I did not change cell shape of corneal endothelial cells: the cells treated with IGF-I at 50 ng/ml maintained polygonal morphology regardless of the duration of exposure. IGF-I did not alter collagen phenotypes either qualitatively or quantitatively: the treated cells continued to synthesize types IV and VIII collagen, as did the control cells. The steady-state levels of alpha 2(I) collagen RNA and alpha 2(IV) RNA were not altered by IGF-I treatment. Immunohistochemical analysis showed that IGF-I is present in corneal endothelium in vivo, while the underlying Descemet's membrane demonstrated no staining. Corneal endothelial cells also produce IGF binding protein-2 (IGFBP-2), which appears to bind IGF-I that has been introduced exogenously in the medium. Further investigation as to how the signals of IGF-I were transmitted for the biological activities demonstrated that the expression of insulin receptor substrate-1 (IRS-1) is up-regulated by IGF-I treatment, while PLC-gamma 1 expression is not altered by this growth factor.(ABSTRACT TRUNCATED AT 250 WORDS)

Maximum likelihood estimation of the heterogeneity of substitution rate among nucleotide sites

This paper presents a maximum likelihood approach to estimating the variation of substitution rate among nucleotide sites. We assume that the rate varies among sites according to an invariant+gamma distribution, which has two parameters: the gamma parameter alpha and the proportion of invariable sites theta. Theoretical treatments on three, four, and five sequences have been conducted, and computer program have been developed. It is shown that rho = (1 + theta alpha)/(1 + alpha) is a good measure for the rate heterogeneity among sites. Extensive simulations show that (1) if the proportion of invariable sites is negligible, i.e., theta = 0, the gamma parameter alpha can be satisfactorily estimated, even with three sequences; (2) if the proportion of invariable sites is not negligible, the heterogeneity rho can still be suitably estimated with four or more sequences; and (3) the distances estimated by the proposed method are almost unbiased and are robust against violation of the assumption of the invariant + gamma distribution.

Distinct aspects of neuronal differentiation encoded by frequency of spontaneous Ca2+ transients

Stimulation of transient increases in intracellular calcium (Cai2+) activates protein kinases, regulates transcription and influences motility and morphology. Developing neurons generate spontaneous Cai2+ transients, but their role in directing neuronal differentiation and the way in which they encode information are unknown. Here we image Ca2+ in spinal neurons throughout an extended period of early development, and find that two types of spontaneous events, spikes and waves, are expressed at distinct frequencies. Neuronal differentiation is altered when they are eliminated by preventing Ca2+ influx. Reimposing different frequency patterns of Ca2+ elevation demonstrates that natural spike activity is sufficient to promote normal neurotransmitter expression and channel maturation, whereas wave activity is sufficient to regulate neurite extension. Suppression of spontaneous Ca2+ elevations by BAPTA loaded intracellularly indicates that they are also necessary for differentiation. Ca2+ transients appear to encode information in their frequency, like action potentials, although they are 10(4) times longer in duration and less frequent, and implement an intrinsic development programme.

[Causes of postoperative recurrent varicose veins of lower extremities]

We analysed venograms of recurrent varicose veins in 180 cases (206 lower limbs). Deep vein valvular insufficiency resulted in varicose veins in 52.9% cases, and post-thrombotic syndrome in 18.9%. The causes of postoperative recurrent varicose veins varied: blindly performed single superficial veins operation, low ligation of the long saphenous trunk, incomplete stripping of varicose veins, missing of the short varicose saphena or incomplete ligation of the perforating veins and failure of deep vein valvular repairs. Venography is of value in making correct diagnosis and choosing appropriate operations.

Regulation of sialyltransferase activities by phosphorylation and dephosphorylation

The composition of tissue gangliosides is thought to result mainly from the active regulation and selective expression of specific enzymes responsible for their metabolism. In the last few years, we have purified several rat brain sialyltransferases to homogeneity; the availability of these highly purified enzymes enabled us to investigate their regulation and expression at the molecular level. Thus, we studied the regulation of sialyltransferase activities, in particular, CMP-NeuAc:GM1 and CMP-NeuAc:LacCer sialyltransferases by a phosphorylation/dephosphorylation mechanism. Protein kinase C was added to a standard enzyme assay mixture containing [gamma-32P]ATP, and the activity of the enzyme was measured after various incubation times. We found that treatment of several sialyltransferases by protein kinase C decreased their activities in a time-dependent manner. Analyses of 32P-labeled amino acids revealed that the major phosphorylation site of CMP-NeuAc:GM1 alpha 2-->3 sialyltransferase (ST-IV) was serine and that for CMP-NeuAc:LacCer alpha 2-->3 sialyltransferase (ST-I) was primarily threonine. Partial recovery of the enzyme activity could be achieved by treatment of the phosphorylated sialyltransferases with rat brain protein phosphatase. We conclude that the activities of sialyltransferases can be modulated by protein kinase C and protein phosphatase and this may represent a potential regulatory mechanism for ganglioside biosynthesis.

The size distribution of insertions and deletions in human and rodent pseudogenes suggests the logarithmic gap penalty for sequence alignment

The size distributions of deletions, insertions, and indels (i.e., insertions or deletions) were studied, using 78 human processed pseudogenes and other published data sets. The following results were obtained: (1) Deletions occur more frequently than do insertions in sequence evolution; none of the pseudogenes studied shows significantly more insertions than deletions. (2) Empirically, the size distributions of deletions, insertions, and indels can be described well by a power law, i.e., fk = Ck-b, where fk is the frequency of deletion, insertion, or indel with gap length k, b is the power parameter, and C is the normalization factor. (3) The estimates of b for deletions and insertions from the same data set are approximately equal to each other, indicating that the size distributions for deletions and insertions are approximately identical. (4) The variation in the estimates of b among various data sets is small, indicating that the effect of local structure exists but only plays a secondary role in the size distribution of deletions and insertions. (5) The linear gap penalty, which is most commonly used in sequence alignment, is not supported by our analysis; rather, the power law for the size distribution of indels suggests that an appropriate gap penalty is wk = a + b ln k, where a is the gap creation cost and blnk is the gap extension cost. (6) The higher frequency of deletion over insertion suggests that the gap creation cost of insertion (ai) should be larger than that of deletion (ad); that is, ai - ad = ln R, where R is the frequency ratio of deletions to insertions.

Spontaneous calcium transients regulate neuronal plasticity in developing neurons

Calcium ions play critical roles in neuronal differentiation. We have recorded transient, repeated elevations of calcium in embryonic Xenopus spinal neurons over periods of 1 h in vitro and in vivo, confocally imaging fluo 3-loaded cells at 5 s intervals. Calcium spikes and calcium waves are found both in neurons in culture and in the intact spinal cord. Spikes rise rapidly to approximately 400% of baseline fluorescence and have a double exponential decay, whereas waves rise slowly to approximately 200% of baseline fluorescence and decay slowly as well. Imaging of fura 2-loaded neurons indicates that intracellular calcium increases from 50 to 500 nM during spikes. Both spikes and waves are abolished by removal of extracellular calcium. Developmentally, the incidence and frequency of spikes decrease, whereas the incidence and frequency of waves are constant. Spikes are generated by spontaneous calcium-dependent action potentials and also utilize intracellular calcium stores. Waves are produced by a mechanism that does not involve classic voltage-dependent calcium channels. Spikes are required for expression of the transmitter GABA and for potassium channel modulation. Waves in growth cones are likely to regulate neurite extension. The results demonstrate the roles of a novel signaling system in regulating neuronal plasticity, that operates on a time scale 10(4) times slower than that of action potentials.

Chemotropism in nerve regeneration studied in tissue culture

The neurotropic effect of the distal stump of transected sciatic nerve on regenerating axons emerging from the proximal stump was investigated in rats by the coculture of excised neonatal dorsal root ganglia and segments of degenerated and nondegenerated sciatic nerves. In all cultures, neurites from the ganglion extended directly towards the degenerated distal stump and not towards the undegenerated nerve segment. Analysis of the supernatants of nerve homogenates by native polyacrylamide gel electrophoresis demonstrated that 250 and 18 kDa proteins were upregulated in the degenerated distal stumps and that 89, 67 and 65 kDa proteins were expressed by these stumps but not by normal nerve. Placement of the individual protein strips, cut from the gels, in dissociated cultures of dorsal root ganglion cells showed that the 89 and 18 kDa strips possessed strong neurotropic activity. Neurons survived selectively on these strips and outgrowing neurites elongated on the strips, parallel to the direction of the band. When explanted dorsal root ganglia were cultured along with the strips, outgrowing neurites extended selectively towards those containing the 89 and 18 kDa bands. It is concluded that these bands contain chemotropic substances, the nature of which requires further investigation.

Encircling suture method in the treatment of femoral venous valvular incompetency

Many patients with chronic venous insufficiency syndrome caused by the "relative valvular incompetency" with venous dilatation. Eighty-six per cent of the cases can be cured by reducing the femoral venous diameter by simply using the encircling suture method just distal to the first femoral valvular sinus. Our preliminary results suggest that such a method of surgical treatment is simple and efficient.

Tityustoxin-K alpha, from scorpion venom, blocks voltage-gated, non-inactivating potassium current in cultured central neurons

Whole-cell voltage-clamp was used to examine the effects of tityustoxin-K alpha (TsTX-K alpha), from the venom of the scorpion Tityus serrulatis, on voltage-gated K+ currents in cultured hippocampal neurons and cerebellar granule cells. Slowly activating, noninactivating outward currents (IK) were generated by depolarizing steps from a holding potential of -60 mV to potentials positive to -40 mV. TsTX-K alpha produced a dose-dependent block of the sustained outward current. The fraction of total current blocked ranged from 10 to 60% over a concentration range of 2.5-120 nM in both cerebellar and hippocampal neurons. A hyperpolarizing prepulse to -100 mV was used to generate a rapidly inactivating current with properties like those of IA. When IA was isolated pharmacologically (with 5-10 mM TEA to block IK) or by subtracting IK from total outward current, TsTX-K alpha had no effect on the IA in either cell type. TsTX-K alpha also had no apparent effect on the leak conductance or on the inward rectifier current in these cells. The data indicate that TsTX-K alpha in cultured mammalian neurons is a potent and selective blocker of a voltage-gated, non-inactivating K+ current with properties like those of a delayed rectifier.

Spontaneous neuronal calcium spikes and waves during early differentiation

Calcium ions play critical roles in neuronal development, but the factors that govern spontaneous fluctuations in intracellular calcium are not well understood. Transient, repeated elevations of calcium in embryonic Xenopus spinal neurons have been recorded over periods of 1 hr in vitro and in vivo, confocally imaging fluo-3-loaded cells at 5 sec intervals. Calcium spikes and calcium waves are found both in neurons in culture and in the intact spinal cord. Spikes rise rapidly to approximately 400% of baseline fluorescence and have a characteristic double exponential decay, while waves rise slowly to approximately 200% of baseline fluorescence and decay slowly as well. Imaging of fura-2-loaded neurons indicates that intracellular calcium increases from 50 to 500 nM during spikes. Both spikes and waves are abolished by removal of extracellular calcium. Developmentally, the incidence and frequency of spikes decrease while the incidence and frequency of waves are constant. Spikes are generated by spontaneous calcium-dependent action potentials that can be triggered by low-threshold, T-type calcium current and are eliminated by agents that block voltage-dependent calcium channels. They can be elicited by depolarization, are generated in an all-or-none manner, and are rapidly and bidirectionally propagated. Spikes also utilize intracellular calcium stores, since blocking release from stores substantially reduces their amplitude. Waves are not elicited by depolarization nor by activation of glutamate receptors, and are propagated at a rate consistent with diffusion of calcium. Waves are blocked by Ni2+ at a higher concentration than required to block classical voltage-dependent calcium channels. Previous work now suggests that spikes are required for expression of the transmitter GABA and for potassium channel modulation. The present study indicates that waves in growth cones are likely to regulate neurite extension.

Increased protein kinase C and isozyme redistribution in pressure-overload cardiac hypertrophy in the rat

Protein kinase C (PKC) activity and isozyme distribution were evaluated during development of pressure-overload-induced cardiac hypertrophy. Three-week-old rats were loosely banded on the ascending aorta (left ventricular hypertrophy [LVH] group). Two weeks later, when left ventricular mass was 50% greater than in the sham-operated control group and cardiac mass was still rapidly increasing beyond that of normal growth, PKC activity and [3H]phorbol 12,13-dibutyrate (PDBu) binding capacity were determined. In LVH, PKC activity was 119 +/- 14%, 158 +/- 17%, and 152 +/- 9% of the control value in cytosol, membrane, and nuclear-cytoskeletal fractions, respectively (n = 9 or 10). [3H]PDBu binding assay revealed increased PKC concentration in LVH cytosolic (control, 0.51 +/- 0.06 pmol/L per milligram; LVH, 0.78 +/- 0.09 pmol/L per milligram; n = 5; P < .05) and membrane fractions (control, 1.33 +/- 0.15; LVH, 2.32 +/- 0.39; n = 5; P < .05). Scatchard analysis indicated no difference in Kd values between control and LVH groups. Immunoblot analysis using PKC isoform-specific antibodies showed that both Ca(2+)-dependent (alpha and beta) and Ca(2+)-independent (delta, epsilon, and zeta) isoforms were present in the left ventricle. Compared with the control value, there was increased concentration in the membrane and nuclear-cytoskeletal fractions for beta 1,2 and epsilon and in the cytosol for beta 1,2. PKC-delta could be detected only in the nuclear-cytoskeletal fraction and was not changed in LVH. PKC-alpha and -zeta were present in all three fractions but were not altered in LVH. These data indicate that PKC activity and concentration increase during development of LVH induced by pressure overload. The increased PKC isozymes were mainly limited to PKC-beta 1,2 and PKC-epsilon, and the increase was present mainly in the membrane and nuclear-cytoskeletal fractions.

Lung cancer among tin miners in southeast China: silica exposure, silicosis, and cigarette smoking

The Dachang Tin Mine is an industrial facility with high rates of lung cancer compared to the resident population in Guangxi province in southern China. Historically, exposure to silica dust was very high in the 1950s, falling in recent years to levels in keeping with international standards. Radon levels in the mine are low. We report the findings of a case-control study nested into a cohort study on miners working in Dachang. Cases of lung cancer among miners incident from 1973-1989 were obtained from local comprehensive medical records covering workers employed at the mine. These were matched approximately 3 to 1 with miners randomly chosen from the district surrounding the mine within the same birth decade. Matched odds ratios of 2.42 (95% confidence limit [CL] 1.3, 4.4) for underground employment, 3.52 (95% CL 1.7, 7.5) for smoking, and 2.04 (95%) CL 1.2, 3.7) for silicosis as determined on chest film were noted. Multifactor analysis of unconditional logistic regression showed that among the risk factors for excess mortality from lung cancer only the years spent drilling underground and the cumulative smoking index (product of daily cigarette consumption and number of years smoking) were independent contributors to risk and there was no interaction observed. The presence of silicosis did not contribute to predicting risk independently of the years spent underground.

Further studies of a maximum-likelihood yes-no procedure

Absolute thresholds were estimated for pure tones of 500, 1000, and 2000 Hz using both a maximum-likelihood yes-no procedure and a traditional three-down one-up forced-choice adaptive procedure. Threshold estimates obtained with the two procedures were highly correlated. In the maximum-likelihood yes-no procedure, the false-alarm probability was poorly estimated. A simple change in that procedure produced less-biased estimates of the false-alarm rate. In a second experiment, the influence of the false-alarm rate on the threshold estimates was investigated. The listeners' absolute thresholds were estimated when they adopted either a liberal or conservative criterion for detecting the signals. Data were collected using both a constant-stimulus yes-no procedure and a maximum-likelihood yes-no procedure. Threshold estimates are 5 to 6 dB higher for the low than for the high false-alarm rates. Psychometric functions based on a stimulus-power model provided the best fit to the data obtained with the constant-stimulus method. This stimulus-power model was used to produce the assumed psychometric function in the maximum-likelihood yes-no procedure. Computer simulations were conducted to determine how threshold estimates were affected by the listener's inattention or by mismatches between the slope parameter of the listener's psychometric function and that assumed in the maximum-likelihood procedure.

Mechanisms of brain injury with deep hypothermic circulatory arrest and protective effects of coenzyme Q10

Sixteen dogs, divided randomly into a control group and coenzyme Q10 group (10mg/kg, intraperitoneally before the operation), underwent deep hypothermic circulatory arrest with cardiopulmonary bypass, as is done clinically. At four time points cerebral cortex and cerebrospinal fluid specimens were collected to study free radical formation, energy metabolism, and ultrastructure. During cardiopulmonary bypass cerebral electron spin resonance spectra and malondialdehyde contents were progressively higher than before bypass, especially at the 60 minutes of circulatory arrest and 30 minutes of reperfusion (p1 < 0.01, p2 < 0.05). In the coenzyme Q10 group at the latter two time points, they had increased less than in the control group at same time points (p1 < 0.02, p2 < 0.005). Adenosine triphosphate content in the cortex during bypass decreased gradually from the prebypass level (p1 < 0.02, p2 = p3 < 0.001), while lactate in cerebrospinal fluid increased (p1 < 0.05, p2 = p3 < 0.001). In the coenzyme Q10 group, adenosine triphosphate at the latter two time points was greater than that in the control group (p1 = p2 < 0.05), while the lactate changes were not significantly different from control at each time point (all p > 0.05). Ultrastructure of the cortex was normal before bypass and almost normal during bypass, but it was obviously abnormal at 60 minutes of circulatory arrest and more seriously abnormal at 30 minutes of reperfusion. In the coenzyme Q10 group the abnormality was obviously reduced. The results suggest that oxygen-derived free radicals and abnormal energy metabolism might play critical roles in brain ischemia/reperfusion injury. Coenzyme Q10 could protect the brain by improving cerebral metabolism.

A panel of radiation hybrids for human chromosome 8

We have developed a panel of radiation hybrids containing fragments of chromosome 8 as the only human material. The human chromosome content of each cell line was determined relative to an ordered map of sequence tagged sites (STSs) specific to chromosome 8. Between one and four fragments of chromosome 8 were identified in each cell line, with an average of 25% of the STSs retained in each line. Subclones of one radiation hybrid were examined to determine whether all cells within a line are homogeneous with respect to chromosome 8 sequence content. There was considerable variability between subclones, with retention rates for individual STSs ranging from 5 to 100% in different clones. Furthermore, a gradient of retention of sequences along the length of one large chromosome fragment was found, suggesting that sequence loss involved deletions from one end of the fragment at early stages in the establishment of the cell line. We have also made use of the radiation hybrids to develop novel sequence tagged sites for the pericentromeric region of chromosome 8.

A model for the correlation of mutation rate with GC content and the origin of GC-rich isochores

Based on the biochemical kinetics of DNA replication and mutagenesis, including misincorporation and correction, a model has been developed for studying the relationships among the mutation rate (u), the G+C content of the sequence (f), and the G+C proportion in the nucleotide precursor pool (N). Also a measure for the next-nucleotide effect, called the maximum capacity of the next-nucleotide effect (MC), has been proposed. Under the normal physiological conditions of mammalian germ cells, our results indicate: (1) the equilibrium G+C content in a sequence is approximately equal to the G+C proportion in the nucleotide precursor pool, i.e., f approximately N, which is independent of the next-nucleotide effect; (2) an inverted-V-shaped distribution of mutation rates with respect to G+C contents is predicted, when the next-nucleotide effect is week, i.e., MC approximately 1; (3) the distribution becomes flatter (i.e., inverted-U-shaped) as MC increases, but the peak at 50% GC is still observed when MC < 2; and (4) the peak disappears when MC > 2.8, that is, when the next-nucleotide effect becomes strong. Our results suggest that changes in the relative concentrations of nucleotide precursors can cause variations among genes both in mutation rate and in G+C content and that compositional isochores (DNA segments with a homogeneous G+C content) can arise in a genome due to differences in replication times of DNA segments.

Corneal endothelial modulation: bFGF as direct mediator and corneal endothelium modulation factor as inducer

PURPOSE

Previously reported from this laboratory are two distinct factors responsible for corneal endothelium modulation: basic fibroblast growth factor (bFGF) and the corneal endothelium modulation factor (CEMF) that is released by inflammatory cells. The altered phenotypes mediated by these two distinct factors--marked increase in cell proliferation, cell shape changes, and synthesis of fibrillar collagens--are identical. The current study sought to determine if bFGF is the direct mediator for corneal endothelium modulation and if CEMF plays a role in inducing bFGF production.

METHODS

bFGF synthesis mediated by CEMF was analyzed by immunoblot assay; cycloheximide was used to block protein synthesis. bFGF-Specific antisense oligonucleotide primer was used to inhibit CEMF-mediated bFGF synthesis and to block further the autocrine activity of bFGF. Cell proliferation was measured by cell counting. The steady-state levels of RNA were determined by Northern blot analysis. CEMF was further purified to homogeneity by sequential electrophoresis, elution, and renaturation of protein.

RESULTS

The synergistic effect of CEMF and bFGF on corneal endothelial cells was measured by their growth-promoting activity on quiescent corneal endothelial cells. There was a dose-dependent cell proliferation mediated by bFGF at any given CEMF concentration. Thus, bFGF at 10 ng/ml with CEMF at 2.5 micrograms/ml demonstrated saturable synergistic activity on endothelial cell proliferation. When the steady-state levels of collagen RNA were measured under these conditions, the untreated cells showed the doublets of 5.6 and 5.0 kb of alpha 2(I) collagen RNA. The cells treated simultaneously with bFGF and CEMF contained mostly lower transcript, compared to the significant level of upper transcript in control cells. However, there was no significant change in the level of 6.9-kb type IV collagen RNA qualitatively or quantitatively; nonetheless, the level of alpha 2(IV) collagen RNA was lowest in cells treated with bFGF plus CEMF. Neither exogenous bFGF nor CEMF caused induction of bFGF messenger RNA in corneal endothelial cells, whereas simultaneous treatment with bFGF and CEMF selectively enhanced the 4.9-kb transcript. When protein synthesis was inhibited by cycloheximide, bFGF synthesis was blocked in the presence of CEMF, leading to inhibition of corneal endothelium modulation. The effect on endothelial cell growth of bFGF antisense primer was analyzed. Antisense primer blocked by 50% the enhanced growth potential mediated by bFGF induced with CEMF. Finally, CEMF was purified to homogeneity: the purified protein is approximately 17 kD and assumes the modulating activities.

CONCLUSIONS

These findings suggest that de novo synthesis of bFGF induced by CEMF is required for corneal endothelium modulation.

In vitro methylation of Escherichia coli 16S rRNA by tRNA (m5U54)-methyltransferase

16S rRNA, isolated from Escherichia coli or synthesized in vitro, is methylated by tRNA (m5U54)-methyltransferase (RUMT) and S-adenosyl-L-methionine to give ribothymidine (m5U). By methylation studies of 16S rRNA fragments, nearest-neighbor analysis, and nuclease protection experiments, the site of methylation was identified as U788. We have previously shown that the substrate consensus sequence for the T-arm of tRNA consists of a 2-5 base-pair stem and a 7-base loop, with certain constraints on base substitutions within the loop, and in the first two bases which close the loop [Gu, X., & Santi, D. V. (1991) Biochemistry 30, 2999-3002]. U788 of 16S rRNA is within a 9-base loop of a predicted stem-loop structure of 16S rRNA. If Ado substitution is allowed at the third and seventh positions of the loop and the first and ninth bases of the loop form an A-C base pair, the resulting stem-loop falls within the RUMT consensus sequence of the T-arm of tRNA. Individual mutants of the tRNA T-arm at these positions confirm that the substitutions are allowable, and expand the previous consensus sequence. Further, prevention of 7-base loop formation by requiring C-C base-pair formation at the loop closure abolishes substrate activity. RUMT forms a complex with Syn 16S rRNA which can be isolated on nitrocellulose filters or by SDS-PAGE electrophoresis. The enzyme also catalyzes exchange of tritium of [3H]Ura-16S rRNA for protons of water. By analogy with studies with tRNA [Gu, X., & Santi, D. V. (1991) Biochemistry 31, 10295-10302], the mechanism of methylation is proposed to involve formation of a covalent, albeit reversible, Michael adduct with the target U788 of 16S rRNA.

Action potentials, calcium transients and the control of differentiation of excitable cells

Calcium influx via action potentials in differentiating nerve and muscle is regulated principally by the expression of potassium currents. Transient elevations of intracellular calcium in spontaneously active cells are necessary for normal neuronal development. The mechanisms that connect calcium elevations to long term developmental change are likely to be utilized in the mature nervous system.

Enzymatic mechanism of tRNA (m5U54)methyltransferase

tRNA (m5U54)methyltransferase (RUMT) catalyzes the methylation of uridine 54 of transfer RNA by S-adenosyl-L-methionine. In this report, we present the enzymatic mechanism of RUMT, including the stereochemical course of the methylation reaction, and discuss RUMT-tRNA recognition. As part of its enzymatic mechanism, we postulate that RUMT catalyzes the disruption of RNA-RNA contacts. We also show that many nucleotide substitutions can be made in the T-loop of tRNA without affecting RUMT binding, indicating that the recognition of the T-loop by RUMT is not stringent.

Patterns of biosynthesis and accumulation of hydrocarbons and contact sex pheromone in the female German cockroach, Blattella germanica

De novo synthesis of contact female sex pheromone and hydrocarbons in Blattella germanica was examined using short in vivo incubations. Accumulation of pheromone on the epicuticular surface and the internal pheromone titer were related to age-specific changes in hydrocarbon synthesis and accumulation in normal and allatectomized females. The incorporation of radiolabel from [1-14C]propionate into the cuticular methyl ketone pheromone fraction was positively related to corpora allata activity during two gonotrophic cycles. During peak pheromone production the total internal lipid fraction contained greater titers of pheromone than the cuticular surface, and it too exhibited a cycle internally, preceding the rise in external pheromone. This suggests that synthesis and accumulation of pheromone internally are followed by transport of pheromone to the epicuticular surface where it accumulates. Radiolabel was incorporated efficiently into both cuticular and internal hydrocarbons after the imaginal molt and until the peak of pheromone synthesis, but it declined to lower levels before ovulation and throughout pregnancy. The internal hydrocarbon titer decreased 58% after oviposition, suggesting deposition in the egg case. It remained relatively unchanged during pregnancy and increased again during the second gonotrophic cycle. In allatectomized females, hydrocarbon synthesis was reduced relative to control females until oviposition in the latter. However, subsequent rates of hydrocarbon synthesis in allatectomized females (without oothecae) exceeded the rates in sham-operated females (with oothecae). In the absence of ovarian uptake of hydrocarbons, the internal titer increased without the decline found in control females at oviposition. As internal hydrocarbons increased, so did cuticular hydrocarbons and both internal and cuticular methyl ketone pheromones. These patterns corresponded well with feeding patterns in sham-operated and allatectomized females, suggesting that pheromone production is normally regulated by stage-specific feeding-induced hydrocarbon synthesis (precursor accumulation internally) and juvenile hormone-induced conversion of hydrocarbon to pheromone. They also suggest that both the cuticle and the ovaries might be target sites for hydrocarbon and possibly methyl ketone deposition.

Purification and characterization of CMP-N-acetylneuraminic acid:lactosylceramide (alpha 2-3) sialyltransferase (GM3-synthase) from rat brain

CMP-N-acetylneuraminic acid:lactosylceramide (alpha 2-3) sialyltransferase (GM3-synthase) was purified to homogeneity from a Triton CF-54 extract of young rat brain. The enzyme was separated by affinity chromatography on CDP-Sepharose column and resolved by linear NaCl gradient elution from the same adsorbent. Final purification of GM3-synthase was achieved by chromatography on a "lactosylceramide acid"-Sepharose column and specific elution with lactosylceramide. The enzyme activity was highest at pH 6.5 and required the presence of Triton CF-54 (0.15%) and Mn2+ (10 mM) for its full activity. The product of the reaction catalyzed by the enzyme was identified as GM3 based on its mobility on thin layer chromatographic plates using two different solvent systems. Comparison with several glycolipid substrates showed high specificity of GM3-synthase for lactosylceramide. The apparent Km value for lactosylceramide and CMP-N-acetylneuraminic acid were 80 and 210 microM, respectively. The apparent molecular mass of the enzyme determined on SDS-polyacrylamide gel electrophoresis was 76 kDa.

[Preliminary experiments on the mode of action of oxalysine on Candida albicans and C. parapsilosis]

Oxalysine, [formula: see text] is a novel anti-fungal antibiotic isolated from Streptomyces roseoviridofuscus n. sp.. MIC values 0.8-3.1 micrograms/ml suggested a good activity of oxalysine against Candida parapsilosis when compared to Amphotericin-B and 5-Fluorocytosine. The MIC for Trichophyton rubrum and Microsporeum gypseum range from 1.56-3.13 micrograms/ml. Transportation of radioactivity labelled (3H)-Lysine compete with oxalysine was used to characterize Lysine permease in Candida albicans. The results showed that oxalysine 10-folds did not reduce the rate of (3H)-Lysine uptake. This showed low affinity of lysine permease to oxalysine in Candida albicans. When the leakage of U V 260 nm-absorbing materials was used as the evidence of permeability of the cell membrane. Oxalysine was not observed to cause leakage of cellular constituents. The result showed that the action of oxalysine is not on the cell membrane of the microorganism. The incorporations of (14C)-Methione and (14C)-Adenine were used as a method of measuring the antimicrobial action of the drug oxalysine is on protein and/or nucleic acid synthesis. It was found that oxalysine 0.4 mmol/L did not significantly inhibit their incorporations into protein and/or DNA, but strongly inhibit the incorporation of (14C)-Adenine into RNA.

Low-threshold Ca2+ current and its role in spontaneous elevations of intracellular Ca2+ in developing Xenopus neurons

Amphibian spinal neurons exhibit spontaneous elevations of intracellular calcium at early stages of development. The underlying calcium influx involves high-voltage-activated (HVA) currents. To begin to understand how they are triggered, we have studied the biophysical properties and developmental function of low-voltage-activated (LVA) T-type calcium current of neurons cultured from the embryonic neural plate. T current was recorded from young neurons (6-9 hr in vitro) and from mature neurons (18-48 hr in vitro) using whole-cell voltage clamp. For both young and mature neurons, T current has a low threshold and is activated at membrane potentials positive to -60 mV in 2 mM extracellular calcium. The current is maximal at -35 mV with a mean peak amplitude of approximately 50 pA. Nickel blocks both LVA and HVA currents, but the former are 20-fold more sensitive. Amiloride also blocks T current selectively. T current is recorded in 87% of young neurons. This percentage drops to 67% in mature neurons after 1 d in culture and to 35% in mature neurons after 2 d in culture. There are no significant developmental changes in T current threshold, peak density, time course of activation and inactivation, and pharmacological sensitivity to blockers from 6 to 48 hr in culture. Spontaneous transient calcium elevations in young neurons assayed by fluo-3 fluorescence are blocked by nickel or amiloride at concentrations that specifically block T current. T current has the lowest threshold among other inward currents in young neurons. Moreover, mathematical simulations show that T current lowers the threshold of the action potential by 15 mV. We conclude that T current can depolarize cells and trigger action potentials, and constitutes part of the cascade of events leading to spontaneous elevations of intracellular calcium in cultured neurons at early stages of differentiation.