The effect of halothane on the action of alcuronium in the dog.

The effect of halothane on the action of alcuronium on neuromuscular transmission was studied in the intact dog. Electrical and mechanical evoked responses from stimulation of the ulnar nerve were recorded. The administration of 0.5% halothane prolonged the duration of action of alcuronium by about 50%.     

A new approach to protein fold recognition.

The prediction of protein tertiary structure from sequence using molecular energy calculations has not yet been successful; an alternative strategy of recognizing known motifs or folds in sequences looks more promising. We present here a new approach to fold recognition, whereby sequences are fitted directly onto the backbone coordinates of known protein structures. Our method for protein fold recognition involves automatic modelling of protein structures using a given sequence, and is based on the frameworks of known protein folds. The plausibility of each model, and hence the degree of compatibility between the sequence and the proposed structure, is evaluated by means of a set of empirical potentials derived from proteins of known structure. The novel aspect of our approach is that the matching of sequences to backbone coordinates is performed in full three-dimensional space, incorporating specific pair interactions explicitly.     

Isolation and characterization of genomic and cDNA clones of human erythropoietin

The glycoprotein hormone erythropoietin regulates the level of oxygen in the blood by modulating the number of circulating erythrocytes, and is produced in the kidney or liver of adult and the liver of fetal or neonatal mammals. Neither the precise cell types that produce erythropoietin nor the mechanisms by which the same or different cells measure the circulating oxygen concentration and consequently regulate erythropoietin production are known. Cells responsive to erythropoietin have been identified in the adult bone marrow, fetal liver or adult spleen. In cultures of erythropoietic progenitors, erythropoietin stimulates proliferation and differentiation to more mature red blood cells. Detailed molecular studies have been hampered, however, by the impurity and heterogeneity of target cell populations and the difficulty of obtaining significant quantities of the purified hormone. Highly purified erythropoietin may be useful in the treatment of various forms of anaemia, particularly in chronic renal failure. Here we describe the cloning of the human erythropoietin gene and the expression of an erythropoietin cDNA clone in a transient mammalian expression system to yield a secreted product with biological activity.     

Novel preparation for studying excitation-secretion coupling in the isolated single cell

Cellular mechanisms of secretion in exocrine and endocrine glands are technically difficult to study. We present here a model which offers fundamental advantages for studying excitation-secretion coupling at the level of the isolated single cell. The salivary gland of the leech Haementeria ghilianii possesses a unique combination of unusual properties which greatly facilitate research in this area. Its cells are exceptionally large (up to 1 mm in diameter), clearly visible and easy to penetrate with microelectrodes. They do not form a homogeneous population but consist of five distinct histochemical types, secreting a number of identified products such as the fibrinolytic enzyme hementin (for which there is a sensitive assay). The cells generate overshooting calcium-dependent action potentials up to 90 mV in amplitude and with a duration of 200-1,000 ms. One of their most useful and unusual features is a lack of electrical coupling which means that individual cells can be studied in an intact gland without interference from neighbouring cells.     

On-demand single-electron transfer between distant quantum dots

Single-electron circuits of the future, consisting of a network of quantum dots, will require a mechanism to transport electrons from one functional part of the circuit to another. For example, in a quantum computer decoherence and circuit complexity can be reduced by separating quantum bit (qubit) manipulation from measurement and by providing a means of transporting electrons between the corresponding parts of the circuit. Highly controlled tunnelling between neighbouring dots has been demonstrated, and our ability to manipulate electrons in single- and double-dot systems is improving rapidly. For distances greater than a few hundred nanometres, neither free propagation nor tunnelling is viable while maintaining confinement of single electrons. Here we show how a single electron may be captured in a surface acoustic wave minimum and transferred from one quantum dot to a second, unoccupied, dot along a long, empty channel. The transfer direction may be reversed and the same electron moved back and forth more than sixty times-a cumulative distance of 0.25 mm-without error. Such on-chip transfer extends communication between quantum dots to a range that may allow the integration of discrete quantum information processing components and devices.     

Dampening of death pathways by schnurri-2 is essential for T-cell development

Generation of a diverse and self-tolerant T-cell repertoire requires appropriate interpretation of T-cell antigen receptor (TCR) signals by CD4(+?) CD8(+) double-positive thymocytes. Thymocyte cell fate is dictated by the nature of TCR-major-histocompatibility-complex (MHC)-peptide interactions, with signals of higher strength leading to death (negative selection) and signals of intermediate strength leading to differentiation (positive selection). Molecules that regulate T-cell development by modulating TCR signal strength have been described but components that specifically define the boundaries between positive and negative selection remain unknown. Here we show in mice that repression of TCR-induced death pathways is critical for proper interpretation of positive selecting signals in vivo, and identify schnurri-2 (Shn2; also known as Hivep2) as a crucial death dampener. Our results indicate that Shn2(-/-) double-positive thymocytes inappropriately undergo negative selection in response to positive selecting signals, thus leading to disrupted T-cell development. Shn2(-/-) double-positive thymocytes are more sensitive to TCR-induced death in vitro and die in response to positive selection interactions in vivo. However, Shn2-deficient thymocytes can be positively selected when TCR-induced death is genetically ablated. Shn2 levels increase after TCR stimulation, indicating that integration of multiple TCR-MHC-peptide interactions may fine-tune the death threshold. Mechanistically, Shn2 functions downstream of TCR proximal signalling compenents to dampen Bax activation and the mitochondrial death pathway. Our findings uncover a critical regulator of T-cell development that controls the balance between death and differentiation.