Construction and performance of a multiparameter focal plane detector for use on a QMG/2 magnetic spectrometer

The design, construction and performance of a modular, two pressure focal plane detector, 550 mm long, 1000 mm deep and with an active height of 60 mm are described. The detector has been operated with ions ranging from 50 MeV ¹H to 200 MeV ³⁶S. Typical results achieved are 0.5 mm and 0.3° for the spatial and angular resolutions, and 0.7% and 3% for the total energy and energy loss measurements. A height signal is also provided.     

Intracellular sequestration of sodium by a novel Na+/H+ exchanger in yeast is enhanced by mutations in the plasma membrane H+-ATPase. Insights into mechanisms of sodium tolerance

Sodium tolerance in yeast is disrupted by mutations in calcineurin, a Ca2+/calmodulin-dependent protein phosphatase, which is required for modulation of Na+ uptake and efflux mechanisms. Five Na+-tolerant mutants were isolated by selecting for suppressors of calcineurin mutations, and mapped to the PMA1 gene, encoding the plasma membrane H+-ATPase. One mutant, pma1-alpha4, which has the single amino acid change Glu367 --> Lys at a highly conserved site within the catalytic domain of the ATPase, was analyzed in detail to determine the mechanism of Na+ tolerance. After exposure to Na+ in the culture medium, 22Na influx in the pma1 mutant was reduced 2-fold relative to control, consistent with a similar decrease in ATPase activity. Efflux of 22Na from intact cells was relatively unchanged in the pma1 mutant. However, selective permeabilization of the plasma membrane revealed that mutant cells retained up to 80% of intracellular Na+ within a slowly exchanging pool. We show that NHX1, a novel gene homologous to the mammalian NHE family of Na+/H+ exchangers, is required for Na+ sequestration in yeast and contributes to the Na+-tolerant phenotype of pma1-alpha4.     

1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine as a substrate of cytochrome P450 2D6: allosteric effects of NADPH-cytochrome P450 reductase

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a neurotoxin that produces Parkinsonism symptoms in man, has been examined as a substrate of recombinant human cytochrome P450 2D6. When cumene hydroperoxide is used as an oxygen and electron donor, a single product is formed, identified as 4-phenyl-1,2,3,6-tetrahydropyridine. The K(m) for formation of this product (130 microM) is in agreement with the dissociation constants for MPTP binding to the enzyme determined by optical and nuclear magnetic resonance (NMR) spectroscopy. When the reaction is carried out with nicotinamide adenine dinucleotide phosphate (reduced) (NADPH) and recombinant human NADPH-cytochrome P450 reductase, a second product, identified as 1-methyl-4-(4'-hydroxyphenyl)-1,2,3,6-tetrahydropyridine, is formed in addition to 4-phenyl-1,2,3,6-tetrahydropyridine. The K(m) values for formation of these two products are 19 microM and 120 microM, respectively. Paramagnetic relaxation experiments have been used to measure distances between the protons of bound MPTP and the heme iron, and these have been used to construct models for the position and orientation of MPTP in the active site. For the cytochrome alone, a single mode of binding was observed, with the N-methyl close to the heme iron in a position appropriate for the observed N-demethylation reaction. In the presence of the reductase, the data were not consistent with a single mode of binding but could be explained by the existence of two alternative orientations of MPTP in the active site. One of these, characterized by a dissociation constant of 150 microM, is essentially identical to that observed in the absence of the reductase. In the second, which has a K(d) of 25 microM, the MPTP is oriented so that the aromatic ring is close to the heme iron, in a position appropriate for p-hydroxylation leading to the formation of the product seen only in the presence of the reductase. In the case of codeine, another substrate for cytochrome P450 2D6, the addition of reductase had no effect on the nature of the product formed, the dissociation constant, or the orientation in the binding site. These observations show that NADPH-cytochrome P450 reductase has an allosteric effect on the active site of cytochrome P450 2D6 that affects the binding of some substrates but not others.     

Transoesophageal echocardiographic assessment of haemodynamic function during laparoscopic cholecystectomy

We have measured cardiovascular changes associated with insufflation of carbon dioxide and the reverse Trendelenburg position during laparoscopic cholecystectomy, using transoesophageal echocardiography in 13 healthy patients. End-tidal carbon dioxide values increased after insufflation of carbon dioxide, with values significantly (P < 0.05) increased after lateral tilt positioning. Creation of a pneumoperitoneum was associated with increases (P < 0.05) in left ventricular end-systolic wall stress, concomitant with increases (P < 0.01) in peak airway pressure and systemic arterial pressure. In addition, left ventricular end-diastolic area decreased (P < 0.05) after reverse Trendelenburg positioning. Left ventricular ejection fraction was maintained throughout the study.     

Real-time X-ray diffraction study at different scan rates of phase transitions for dipalmitoylphosphatidylcholine in KSCN

A questionnaire survey was carried out to examine the attitudes and practices of Australian and New Zealand intensivists with regard to brain death and organ donation. A return rate of 82.5% was achieved. Fifty-eight per cent had written evidence of their own wishes to donate organs and 94% would agree to donation from a dependent. At least one intensivist is involved in certifying brain death on 95% of occasions. Intensivists are involved in the request for organ donation over 90% of the time although one-third do not believe that it is their role to request organ donation. Although two-thirds believe that the family should always be approached for organ donation, another 52 out of 254 indicated that it was their (the intensivist's) role to decide if families should be asked for organ donation. Possible reasons for not requesting are language or other communication problems, perceptions of cultural differences and degrees of family distress. Twenty per cent of respondents do not provide haemodynamic support before brain death confirmation. Australian and New Zealand intensivists overwhelmingly support the concept of brain death, current methods of confirmation of brain death, organ donation and transplantation. Possible reasons behind loss of potential donors include decisions not to resuscitate both before and after brain death is confirmed. Perceptions of family grief and cultural differences clearly inhibit requests for organ donation. A very few units have an effective policy on approaching families about organ donation. Intensivists have almost exclusive control over requests for organ donation and thus bear a full professional responsibility for this element of hospital practice.