Substrate recognition by human RNase P: identification of small, model substrates for the enzyme

RNase P from HeLa cells can efficiently cleave tRNA precursor molecules in vitro but cannot cleave potential substrates from which the D, anticodon and variable loops and stems of the tRNA moiety have all been removed. However, molecules from which the latter subdomains have been removed individually do serve as substrates. We show here that molecules that contain only a 5' leader sequence, the acceptor stem and the T stem and loop of the tRNA domain, and a bulge as small as one nucleotide downstream from nucleotide 7 in the tRNA sequence at the junction of the two stems, can serve as substrates for human RNase P. The identity of the nucleotide in the bulge is important in determining both the efficiency of the cleavage and the conformation of the substrate and/or the enzyme-substrate complex. We also show that the human enzyme locates the appropriate site for cleavage of its substrates in part by 'measuring' the length of the helices in the acceptor and T stems in both model and natural substrates.

Interaction of neutrophils and endothelium in isolated coronary venules and arterioles

This study reports measurements of porcine neutrophil dynamics in isolated microvessels. Porcine coronary venules and arterioles were isolated, cannulated, and perfused with fluorescently labeled neutrophils at a series of flow velocities. In venules (62.50 +/- 5.41 microns diam) under control conditions, rolling neutrophils were often observed at intraluminal flow velocities ranging from 600 to 6,000 microns/s, and the rolling fraction varied inversely as a function of flow velocity. There was no significant adherence under the control conditions at any of the various flow velocities. Pretreatment of the neutrophils with human recombinant complement 5a (C5a, 10(-8) M) increased adherence at low flow velocities but did not alter the rolling fraction. In contrast to venules, rolling neutrophils were not observed in arterioles (58.80 +/- 5.6 microns diam). Furthermore, neutrophils that were pretreated with C5a did not adhere to the arteriolar endothelium even at low flow velocities. We suggest that 1) isolated microvessels perfused with fluorescently labeled neutrophils are suitable models for the study of the interaction between neutrophils and the microvascular endothelium, 2) shear force plays an important role in neutrophil rolling in coronary venules but is not the major factor that prevents neutrophil rolling and adherence in arterioles, and 3) C5a causes neutrophil adherence in venules but not in arterioles, indicating that different mechanisms underlie the interaction between neutrophils and endothelium in venules and arterioles.

Tyrosine kinases regulate the cytoskeletal attachment of integrin alpha IIb beta 3 (platelet glycoprotein IIb/IIIa) and the cellular retraction of fibrin polymers

Integrins promote cell-substratum and cell-cell adhesion by acting as transmembrane linker molecules between extracellular adhesion proteins and the actin-rich cytoskeleton. The integrin alpha IIb beta 3 (platelet glycoprotein IIb/IIIa) is essential for platelet spreading, aggregation, fibrin clot retraction, and for the transduction of extracellular signals. We examined the effect of the specific tyrosine kinase inhibitor herbimycin A on integrin and cytoskeletal-mediated events in thrombin-stimulated platelets. Incubation of washed platelets for 24 h with herbimycin A (5 microM) abolished the thrombin-stimulated cytoskeletal enzyme activity of pp60c-src in parallel with a reduction in the tyrosine phosphorylation of multiple platelet proteins, as assessed with anti-phosphotyrosine immunoblots. However, thrombin-induced activation of protein kinase C and the production of thromboxane A2 were not altered by herbimycin A. Despite the absence of cytoskeletal pp60c-src enzyme activity, platelet shape change, aggregation, and serotonin release were unaltered following platelet stimulation with thrombin (0.05-1.0 unit/ml). Herbimycin A-treated platelets also demonstrated normal platelet aggregation in response to collagen (5 micrograms/ml), ionophore A23187 (2 microM), and ADP/adrenaline (10 microM each). However, the ability of herbimycin A-treated platelets to retract fibrin gels was significantly reduced. This defect in clot retraction was associated with reduced incorporation of integrin alpha IIb beta 3 into the cytoskeletal fraction of thrombin-aggregated platelets. Our studies suggest that tyrosine kinases in platelets regulate the cytoskeletal attachment of alpha IIb beta 3, as an essential process for the transmission of cellular contractile forces to fibrin polymers.

Adhesion receptor activation of phosphatidylinositol 3-kinase. von Willebrand factor stimulates the cytoskeletal association and activation of phosphatidylinositol 3-kinase and pp60c-src in human platelets

The cytoskeleton participates in the coordinated regulation of intracellular signaling molecules, following agonist stimulation of cells. We have demonstrated that von Willebrand factor (vWF) induced the cytoskeletal association and activation of phosphatidylinositol 3-kinase (PtdIns 3-kinase) in human platelets. The activation of PtdIns 3-kinase coincided with the tyrosine phosphorylation of multiple platelet proteins, as assessed by anti-phosphotyrosine immunoblotting. One of these tyrosine-phosphorylated proteins, pp60c-src, became specifically enriched in the cytoskeletal fraction of vWF-stimulated platelets. The vWF-stimulated cytoskeletal association of PtdIns 3-kinase and pp60c-src required platelet stirring and aggregation, was specifically blocked by an anti-GPIb monoclonal antibody, and was not observed in platelets lacking the glycoprotein Ib/IX complex (Bernard-Soulier syndrome). Pretreatment of normal platelets with 5 mM EDTA (37 degrees C for 90 min) or RGDS (2 mM), which disrupts the binding of various adhesive proteins to platelet integrins and inhibits fibrinogen-mediated platelet aggregation, did not alter the vWF-stimulated activation and cytoskeletal association of PtdIns 3-kinase and pp60c-src. Pretreatment of platelets with acetylsalicylic acid (1 mM) completely abolished vWF-stimulated production of thromboxane A2, dense granule release, and the activation of protein kinase C, without altering the activation and cytoskeletal translocation of PtdIns 3-kinase and pp60c-src. Our results suggest that vWF binding to the platelet adhesion receptor glycoprotein Ib/IX can mediate activation and translocation of both tyrosine and lipid kinase(s) independent of other agonists.

Development of a central matching system for the allocation of cadaveric kidneys: a simulation of clinical effectiveness versus equity

OBJECTIVES

1) To develop a computer-based simulation to prospectively study the impacts of explicitly incorporating different equity criteria into the process of allocating kidneys to recipients, given the scarcity of this resource. 2) To assess the tradeoffs between systems that allocate kidneys based only on medical criteria, systems that allocate kidneys based only on equity criteria, and systems that consider both medical and equity criteria.

METHODS

A computer-based simulation was developed that describes the flows of patients and kidneys. This model provides information at various time points about the number of patients in the system who are awaiting transplants, the number of kidneys available for transplantation, the number of transplantations performed for each matching algorithm, and the number of kidneys discarded (when applicable), as well as the means and standard deviations of the HLA-match scores, number of days from registration to transplantation, and number of days (from registration) of those who are still waiting for transplants. Five different matching algorithms were compared, ranging from determination of the allocation by a single medical criterion (i.e, HLA match) to determination by a single equity criterion (i.e., relative position in the waiting queue). The remaining algorithms represent different strategies of weighting these two considerations. Estimates regarding the main parameters of the model were derived utilizing data collected through the Multiple Organ Retrieval and Exchange Programme of Ontario, Canada.

RESULTS

The simulation was set to run for a period of ten years. A tradeoff between graft survival (or improved HLA matching) and equal treatment of patients regardless of their likelihood to benefit was found. It is clear that an algorithm that allocates kidneys based only on temporal location of patient on the waiting list is likely to be unacceptable because of the very poor average HLA-match scores that it yields. Pool size was found to be a major determinant in the attainment of optimal matching from a medical perspective.

CONCLUSIONS

1) The final choice about any allocation algorithm to be used requires that a value judgment be made, i.e., how great a reduction in HLA-match score should be traded in order to improve equity score (or vice versa). 2) A computer-based simulation model is a feasible way to prospectively test the impact of any given allocation algorithm on any given system.

Selection of guide sequences that direct efficient cleavage of mRNA by human ribonuclease P

Any RNA, when in a complex with another oligoribonucleotide known as an external guide sequence (EGS), can become a substrate for ribonuclease P. Simulation of evolution in vitro was used to select EGSs that bind tightly to a target substrate messenger RNA and that increase the efficiency of cleavage of the target by human ribonuclease P to a level equal to that achieved with natural substrates. The most efficient EGSs form transfer RNA precursor-like structures with the target RNA, in which the analog of the anticodon stem has been disrupted, an indication that selection for the optimal substrate for ribonuclease P yields an RNA structure different from that of present-day transfer RNA precursors.

66A-078:a kappa-opiate receptor agonist for amelioration of spinal spasticity

The effect and mechanism of kappa opiate receptor agonist and high-frequency electrostimulation of acupoints in treating spinal spasticity were studied. The spinal spastic models were made by gradual mechanical compression on the cervical spinal cord of rabbits. 24 prepared rabbits were divided into 3 groups randomly, and each group with 8 rabbits was given intrathecally kappa-receptor agonist 66A-078, kappa-receptor antagonist +66A-078 and normal saline respectively. The degree of spasticity was quantified by both clinical score and electrophysiological examinations. The result showed that the spasticity was markedly inhibited by intrathecal injection of 66A-078 and that the kappa-receptor antagonist (naloxone) reversed this effect. We can infer that the antispastic effect of 66A-078 is mediated by kappa-receptors. This result is helpful in explaining the immediate antispastic mechanism of high-frequency electrostimulation of acupoints discussed in previous study.

Human RNaseP RNA and nucleolar 7-2 RNA share conserved 'To' antigen-binding domains

RNase P in both prokaryotes and eukaryotes is a ribonucleoprotein that cleaves tRNA precursors to generate the 5' termini of the mature tRNAs. Many patients with autoimmune diseases produce antibodies against a 40 kDa protein (designated To or Th antigen) which is an integral component of eukaryotic RNaseP as well as nucleolar 7-2 RNP which is identical to the mitochondrial RNA processing (MRP) RNP. Interestingly, the To antigen found in human cells and the C5 protein, the only protein component of E. coli RNaseP, are antigenically related. In this study, we show that a 56 nucleotide-long sequence, corresponding to nucleotides 20-75 near the 5' end of human RNaseP RNA, is sufficient to bind the To antigen. We previously showed that the human To antigen binds to a short distinct structural domain near the 5' end of human 7-2/MRP RNA. There is no obvious primary sequence homology between the To antigen binding sites in RNaseP RNA and 7-2/MRP RNA; however, these sequences are capable of assuming a similar secondary structure which corresponds to the recently proposed 'cage' structure for RNaseP RNAs and 7-2/MRP RNA (Forster and Altman (1989) Cell 62: 407-409). These data are supportive of the idea that these two RNAs may have evolved from a common progenitor molecule.

Transcutaneous electrical nerve stimulation for treatment of spinal spasticity

Thirty-two patients with spinally originated muscle spasticity were treated with a transcutaneous electrical nerve stimulator, the Han's acupoint nerve stimulator (HANS) via skin electrodes placed over the acupoints on the hand and leg. High frequency (100 Hz), but not the low frequency (2 Hz), stimulation was effective in ameliorating muscle spasticity. While the therapeutic effect lasted for only 10 minutes in the first treatment, it became consolidated after consecutive daily treatment for 3 months. The anti-spastic effect induced by high frequency electrical stimulation can be partially reversed by a high dose of naloxone. The results suggest that the anti-spastic effect elicited by peripheral electrical stimulation is mediated, at least in part, by the endogenous opioid ligand interacting with the kappa opiate receptors, most probably dynorphin, in the central nervous system.

Sports causing most injuries in Hong Kong

A prospective survey was carried out on 2293 patients attending the Sports Injury Clinic in the Prince of Wales Hospital between May 1984 and December 1990. A Sports Injury Report Form was completed for each patient. Subjects in this study represent a group of nonprofessional and non-élite athletes in a metropolitan area. Soccer, basketball, volleyball, long-distance running and cycling in descending order were the five most common sports causing injury. Different sports produced different injury patterns. In four of the five sports, the knee (27.27-50.47%) and the ankle (16.78-24.67%) were the commonest sites of injury. In cycling, the face (19.46%) was the commonest site of injury. There was a higher injury rate to the lower than the upper limb in soccer, basketball, volleyball and long-distance running, with a ratio of upper- to lower-limb injury ranging from 1:1.13 to 1:46.10. In cycling, upper limb injury was more frequent (upper- to lower-limb injury ratio was 1:0.53). Sprain was the commonest injury overall (44.60%). It was also the commonest injury condition in volleyball (55.15%), basketball (55.34%), soccer (51.41%) and long-distance running (39.33%). In cycling, abrasion (24.83%) was commonest.

[Research on anti-idiotypic antibodies to bovine abortus]

Based on the establishment of McAbs to a local Brucella strain S85A, the McAb A7 was selected and tested as a protective one. Using A7 to immunize rabbits, we got high titer anti-idiotypic antibodies which were then proved to possess internal image by competitive inhibiting ELISA and catch blocking ELISA. The anti-idiotypic antibodies were then purified and mixed with glycerin to immunize guinea pigs and mice. The results showed that: immunized guinea pigs and mice had produced certain titer antibodies to Brucella. 79.2% of immunized guinea pigs had been protected from the challenge of 544A 4 months later from primary immunization. The number of T ANAE+ in peripheral blood of immunized mice had increased significantly compared to controls. These results suggest that the anti-idiotypic antibodies not only possess the antigen internal image but have the available immunogenicity stimulate animals producing Ab3 and make them get free from the infection.

Permeability to albumin in isolated coronary venules

This study reports measurements of albumin permeability in isolated coronary venules. The isolated microvessel technique allows the quantification of transmural exchange of macromolecules under tightly controlled physical and chemical conditions. Transvenular exchange of albumin was studied in isolated coronary venules during alterations in filtration rate caused by changes in intravascular pressure. The apparent permeability coefficient of albumin (Pa) at an intraluminal pressure of 11 cmH2O was 3.92 +/- 0.43 x 10(-6) cm/s. Elevating intraluminal pressure to 16 and 21 cmH2O increased Pa to 5.13 +/- 0.57 x 10(-6) and 6.78 +/- 0.66 x 10(-6) cm/s, respectively. Calculation of the true diffusive permeability coefficient of albumin (Pd) at zero filtration rate was 1.54 x 10(-6) cm/s. The product of hydraulic conductance (Lp) and (1 - sigma), where sigma is the solute reflection coefficient, was 3.25 x 10(-7) cm.s-1 x cmH2O-1. At a net filtration pressure of 4-5 cmH2O, diffusion accounts for > 60% of total albumin transport across the venular wall. Transmural albumin flux is very sensitive to filtration rate, rising 6.7% for each cmH2O elevation of net filtration pressure. At 11 cmH2O net filtration pressure, convection accounts for nearly 70% of net albumin extravasation from the venular lumen. We suggest that the isolated coronary venule is a suitable preparation for the study of solute exchange in the heart.

Purification and characterisation of a snake venom phospholipase A2: a potent inhibitor of platelet aggregation

An inhibitor of human platelet aggregation was identified from the venom of an Australian Copperhead snake, Austrelaps superba, as a novel phospholipase A2. The inhibitor was purified to homogeneity by chromatography on Q-Sepharose, S-Sepharose and C8 reverse phase HPLC. The purified phospholipase A2 has a molecular weight of 15 kDa as assessed by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). N-terminal sequence analysis of the platelet inhibitor revealed 70-80% sequence identity to other previously described secretory phospholipase A2. Phospholipase activity of the purified protein was confirmed by the ability of the enzyme to hydrolyse lecithin. Pretreatment of the purified protein with the specific phospholipase A2 inhibitor p-bromophenacyl bromide, resulted in abrogation of both its enzyme and platelet inhibitory activity. The phospholipase A2 inhibited platelet aggregation and serotonin release, induced by a variety of platelet agonists, in a time and dose dependent manner.

Hong Kong Sports Institute: sports medicine and science from theory to practice

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Disruption by methylmercury of membrane excitability and synaptic transmission of CA1 neurons in hippocampal slices of the rat

In order to examine the effects of methylmercury (MeHg) on central synaptic transmission, field potentials were recorded in the CA1 neurons of hippocampal slices by using extracellular microelectrode recording techniques. After stimulation of Schaffer collaterals at low frequency (0.25 Hz), population spikes and excitatory postsynaptic potentials (EPSPs) were recorded at the cell bodies and apical dendrites of CA1 pyramidal cells, respectively. Antidromically activated population spikes were also recorded at the cell bodies of CA1 pyramidal cells by stimulating the alveus. Long-term potentiation (LTP) was induced by application of brief high-frequency stimulation (15 trains of four stimuli per train at 100 Hz) after 25 min of population spike baseline recordings. MeHg was applied to slices acutely by bath perfusion with artificial cerebrospinal fluid (ACSF). At 20-500 microM, MeHg significantly increased and then decreased the amplitudes of, or blocked, the population spikes, EPSPs, and antidromically activated population spikes. Time to increase and time to block of these field potentials were concentration-dependent. Exposure of slices to 4 microM MeHg for 180 min increased but did not reduce the amplitudes of population spikes, EPSPs, or antidromically activated population spikes. The effects of MeHg on population spikes induced by either orthodromic or antidromic stimulation were similar. In the absence of MeHg, application of high-frequency stimulation increased population spike amplitudes by 60-100%. This effect (LTP) could be sustained for more than 2 hr in the absence of MeHg. When 100 microM MeHg was applied concomitantly with high-frequency stimulation, the population spike amplitudes were increased by an additional 20-50% based on the already elevated population spike amplitude by high-frequency stimulation. Subsequently, population spike amplitudes were reduced and finally blocked in a manner similar to the effect of MeHg on population spikes recorded without high-frequency stimulation. Application of MeHg (100 microM) for 20 min prior to high-frequency stimulation did not prevent induction of LTP even though the population spike amplitudes had been decreased by more than 10% of the control level, suggesting that MeHg may not alter induction of LTP. Reversibility of the effects of MeHg was examined by washing slices with MeHg-free ACSF or 1 mM D-penicillamine for 60-120 min after MeHg treatment. Washing slices with MeHg-free ACSF caused at best partial reversal of effects of MeHg. D-Penicillamine, a chelator of MeHg, completely reversed the effects of MeHg on EPSPs but only partially reversed the effects of MeHg on population spikes, antidromically activated population spikes, and LTP.(ABSTRACT TRUNCATED AT 400 WORDS)

Histamine increases venular permeability via a phospholipase C-NO synthase-guanylate cyclase cascade

In this study, we hypothesized that histaminergic increases in venular permeability result from a cascade triggered by activation of phospholipase C (PLC), inducing the synthesis of nitric oxide (NO) and activating guanylate cyclase. The apparent permeability coefficient to albumin (Pa) was measured in isolated porcine coronary venules subjected to constant flow and hydrostatic and oncotic pressures. Histamine (2.5, 5, and 10 microM) transiently and progressively increased Pa. The PLC inhibitor 2-nitro-4-carboxyphenyl N,N-diphenylcarbamate (NCDC; 100 microM) decreased baseline permeability and abolished the effect of histamine. The NO synthase inhibitor NG-monomethyl-L-arginine (L-NMMA; 10 microM) and the guanylate cyclase inhibitor 6-anilinoquinoline-5,8-quinone (LY 83583; 10 microM) also blocked the histamine-induced hyperpermeability. L-Arginine (3 mM) reversed the inhibition by L-NMMA. NG-monomethyl-D-arginine did not influence the effect of histamine. Furthermore, sodium nitroprusside (10 microM) augmented Pa by two- to threefold; this effect was blocked in the presence of LY 83583 but not altered in the presence of NCDC. The results suggest that histamine increases coronary venular permeability by a direct action on the venular endothelial cells through a PLC-NO synthase-guanylate cyclase-signaling cascade.

Real-time coherent image differentiation using a self-pumped phase conjugator with Cu:KNSBN

A technique for real-time coherent image differentiation is described in a device consisting of a self-pumped phase conjugator that uses a copper-doped potassium sodium strontium barium niobate crystal. We demonstrate the proposed technique.

The Johnson antishear device and standard shin pad in the isokinetic assessment of the knee

Isokinetic training and assessment of the knee joint has been the mainstay of rehabilitation, especially in patients with anterior cruciate ligament deficiency. Besides the original shin pad used, the antishear device was introduced by Johnson in 1982. This device has been shown biomechanically to prevent excessive anterior translation of force on the tibia during training. However, there is a need to compare the antishear device and the standard shin pad in the isokinetic assessment. Hence, the major objective of this study is to define, if any, the difference in patient assessment between the new double pad device and the old single shin pad. Ten subjects with no previous history of injury on either knee were tested with the Cybex Isokinetic Dynamometer. There were four men and six women and the mean age was 25.2 years. They were randomized into different test sequences with different shin pads at different speeds. Correlation and paired t tests (P) were performed to find out the correlation and difference between the two devices. There was significant difference in performance assessment between the two devices in knee extension (P < 0.05) but no significant difference in knee flexion (P > 0.05). There was also a high correlation (r > 0.75) between the two devices. It is concluded that because of the significant difference of data generated between the two devices, it is important to select one single device with each patient during a series of testings.

Enhanced self-pumped phase conjugation from 16 degrees -cut KNSBN:Cu

With the maximum coupling coefficient and high internal reflection conditions, the self-pumped phase-conjugation reflectivity of copper-doped potassium sodium strontium barium niobate (KNSBN:Cu) is increased with 16 degrees -cut samples. The response time is also shortened. The resolution property of 16 degrees -cut KNSBN:Cu is determined and a distorted image is corrected by using the 16 degrees -cut sample.