Enhanced interfacial magnetic coupling of Gd /Fe multilayers

The spatial extent zeta(AFM) and strength J(AFM) of the antiferromagnetic (AFM) exchange coupling at buried Gd /Fe interfaces in ferrimagnetic [Gd(50 A)Fe(15,35 A)](15) sputtered multilayers is obtained from combined x-ray resonance magnetic reflectivity and magnetic circular dichroism measurements. zeta(AFM) is 4.1(7) A or approximately 1-2 interatomic distances in bulk Gd and Fe; J(AFM) is 1050(90) K, comparable to the ferromagnetic exchange in bulk Fe.

Regulation of melatonin 1a receptor signaling and trafficking by asparagine-124

Melatonin is a pineal hormone that regulates seasonal reproduction and has been used to treat circadian rhythm disorders. The melatonin 1a receptor is a seven- transmembrane domain receptor that signals predominately via pertussis toxin-sensitive G-proteins. Point mutations were created at residue N124 in cytoplasmic domain II of the receptor and the mutant receptors were expressed in a neurohormonal cell line. The acidic N124D- and E-substituted receptors had high-affinity (125)I-melatonin binding and a subcellular localization similar to the neutral N124N wild-type receptor. Melatonin efficacy for the inhibition of cAMP by N124D and E mutations was significantly decreased. N124D and E mutations strongly compromised melatonin efficacy and potency for inhibition of K(+)-induced intracellular Ca(++) fluxes and eliminated control of spontaneous calcium fluxes. However, these substitutions did not appear to affect activation of Kir3 potassium channels. The hydrophobic N124L and N124A or basic N124K mutations failed to bind (125)I-melatonin and appeared to aggregate or traffic improperly. N124A and N124K receptors were retained in the Golgi. Therefore, mutants at N124 separated into two sets: the first bound (125)I-melatonin with high affinity and trafficked normally, but with reduced inhibitory coupling to adenylyl cyclase and Ca(++) channels. The second set lacked melatonin binding and exhibited severe trafficking defects. In summary, asparagine-124 controls melatonin receptor function as evidenced by changes in melatonin binding, control of cAMP levels, and regulation of ion channel activity. Asparagine-124 also has a unique structural effect controlling receptor distribution within the cell.

Cyclic AMP regulates the calcium transients released from IP(3)-sensitive stores by activation of rat kappa-opioid receptors expressed in CHO cells

We analyzed intracellular Ca(2+)and cAMP levels in Chinese hamster ovary cells expressing a cloned rat kappa opioid receptor (CHO-kappa cells). Although expression of kappa(kappa)-opioid receptors was confirmed with a fluorescent dynorphin analog in almost all CHO-kappa cells, the kappa-specific agonists, U50488H or U69593, induced a Ca(2+) transient only in 35% of the cells. The Ca(2+) response occurred in all-or-none fashion and the half-maximal dosage of U50488H (812.1nM) was higher than that (3.2nM) to inhibit forskolin-stimulated cAMP. The kappa-receptors coupled to G(i/o)proteins since pertussis toxin significantly reduced the U50488H actions on intracellular Ca(2+) and cAMP. The Ca(2+) transient originates from IP(3)-sensitive internal stores since the Ca(2+) response was blocked by a PLC inhibitor (U73122) or by thapsigargin depletion of internal stores while removal of extracellular Ca(2+) had no effect. Interestingly, application of dibutyryl cAMP (+ 56.2%) or 8-bromo-cAMP (+ 174.7%) significantly increased the occurrence of U50488H-induced Ca(2+) mobilization while protein kinase A (PKA) inhibitors, Rp-cAMP (-32.3%) or myr-psi PKA (-73.9%) significantly reduced the response. Therefore, it was concluded that cAMP and PKA activity can regulate the Ca(2+) mobilization. These results suggest that the kappa receptor-linked cAMP cascade regulates the occurrence of kappa-opioid-mediated Ca(2+) mobilization.

Orphanin-FQ/nociceptin (OFQ/N) modulates the activity of suprachiasmatic nucleus neurons

Neurons in the suprachiasmatic nucleus (SCN) constitute the principal circadian pacemaker of mammals. In situ hybridization studies revealed expression of orphanin-FQ/nociceptin (OFQ/N) receptor (NOR) mRNA in the SCN, whereas no expression of mRNA for preproOFQ/N (ppOFQ/N) was detected. The presence of OFQ/N peptide in the SCN was demonstrated by radioimmunoassay. SCN neurons (88%) responded dose-dependently to OFQ/N with an outward current (EC50 = 22.3 nM) that was reduced in amplitude by membrane hyperpolarization and reversed polarity near the theoretical potassium equilibrium potential. [Phe1psi(Ch2-NH)Gly2]OFQ/N(1-13)NH2 (3 microM), a putative NOR antagonist, activated a small outward current and significantly reduced the amplitude of the OFQ/N-stimulated current. OFQ/N reduced the NMDA receptor-mediated increase in intracellular Ca2+. When injected unilaterally into the SCN of Syrian hamsters housed in constant darkness, OFQ/N (1-50 pmol) failed to alter the timing of the hamsters' wheel-running activity. However, injection of OFQ/N (0.1-50 pmol) before a brief exposure to light during the midsubjective night significantly attenuated the light-induced phase advances of the activity rhythm. These data are consistent with the interpretation that OFQ/N acting at specific receptors modulates the activity of SCN neurons and, thereby, the response of the circadian clock to light.

Melatonin receptor potentiation of cyclic AMP and the cystic fibrosis transmembrane conductance regulator ion channel

We have used the cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel as a model system to study the cAMP signal transduction pathways coupled to the Xenopus melatonin receptor. During forskolin (Fsk) stimulation, melatonin reduced the amplitude of the CFTR currents in oocytes injected with in vitro transcribed cRNAs for the Xenopus melatonin receptor and CFTR. Pertussis toxin (Ptx) treatment eliminated melatonin inhibition of Fsk stimulated CFTR currents. In oocytes injected with cRNA for melatonin receptors, serotonin receptors (5-HT7), and CFTR Cl- channels, application of melatonin together with serotonin (5-HT) activated an additional inward current showing potentiation of adenylyl cyclases by melatonin receptors. Subthreshold activation of 5-HT7 receptors was sufficient and necessary to permit activation of CFTR channels by melatonin. Preexposure to melatonin desensitized the melatonin receptor mediated response. Therefore, based on this model system, the effects of melatonin in vivo could be either positive or negative modulation of other neuronal inputs, depending on the mode of adenylyl cyclase stimulation.

Cyclic AMP analogs induce synthesis, processing, and secretion of prepro nociceptin/orphanin FQ-derived peptides by NS20Y neuroblastoma cells

Recent studies have shown that cAMP analogs can induce expression of prepro (pp) orphanin FA (OFQ)/nociceptin-related gene products in NS20Y mouse neuroblastoma cells (Saito et al. [1996]. J Biol Chem 271, 15615-15622). Additionally, exposure of NS20Y cells to cAMP analogs promoted neurite outgrowth and large dense-core vesicle formation. Even though an OFQ-like precursor (called 27K) was identified in NS20Y cell extracts, no secretion of OFQ-related peptides was detected. We have used reversed-phase high-performance liquid chromatography combined with a specific radioimmunoassay for OFQ(1-17) to determine if NS20Y cells secrete ppOFQ-derived peptides when stimulated by the cAMP analog ctp-cAMP. We found that NS20Y cells secreted abundant amounts of OFQ-derived products when stimulated by cAMP analogs. We also have determined that secretion of OFQ peptides was both time and concentration dependent and reversible on removal of cAMP analogs from the culture medium. In addition, the opioid agonist D-Pen2-D-Pen5-enkephalin inhibited forskolin-stimulated OFQ peptide secretion. Further, the synthetic glucocorticoid dexamethasone virtually abolished ctp-cAMP-stimulated OFQ peptide secretion. These results suggest that the biosynthesis, processing, and secretion of the OFQ neuropeptide transmitter system can be modulated through intracellular cAMP levels and that these functions are regulated by opioids and molecules involved in mediating the stress response. The NS20Y cell system will be extremely valuable for studying the regulation of OFQ-derived peptides by a variety of intra-cellular and extracellular signaling pathways.

Contribution of serine residues to constitutive and agonist-induced signaling via the D2S dopamine receptor: evidence for multiple, agonist-specific active conformations

Dopamine D2 receptors contain a cluster of serine residues in the fifth transmembrane domain that contribute to activation of the receptor as well as to the binding of agonists. We used rat D2S dopamine receptor mutants, each containing a serine-to-alanine substitution (S193A, S194A, S197A), to investigate the mechanism through which these residues affect activation of the receptor. Activation of the mutant receptor S194A was abolished in an agonist-dependent manner, such that dopamine no longer inhibited cAMP accumulation in C6 glioma cells or activated G protein-regulated K+ channels in Xenopus laevis oocytes, whereas the efficacy of several other agonists was unaffected. Dihydrexidine did not inhibit cAMP accumulation at either S193A or S194A. The decreased efficacy of dihydrexidine at S193A and S194A and dopamine at S194A was associated with a decreased ability to detect a GTP-sensitive high affinity binding state for these agonists. The ability of dopamine to stimulate [35S]guanosine-5'-O-(3-thio)triphosphate binding via S194A also was decreased by approximately 50%. Finally, constitutive stimulation of [35S]guanosine-5'-O-(3-thio)triphosphate binding and inhibition of adenylate cyclase by the D2S receptor was reduced by mutation of either S193 or S194. These data support the existence of multiple active receptor conformations that are differentially sensitive to mutation of serine residues in the fifth-transmembrane domain.

Lead inhibition of N-methyl-D-aspartate receptors containing NR2A, NR2C and NR2D subunits

The potency of Pb2+ inhibition of glutamate-activated currents mediated by N-methyl-D-aspartate (NMDA) receptors was dependent on the subunits composing the receptors when functionally expressed in Xenopus laevis oocytes. Pb2+ reduced the amplitudes of glutamate-activated currents and shifted the agonist EC50 values of NMDA receptors consisting of different subunit compositions. The IC50 values for Pb2+ ranged from 1.52 to 8.19 microM, with a rank order of potency of NR1b-2A > NR1b-2C > NR1b-2D > NR1b-2AC. For NR1b-2AC NMDA receptors, the IC50 value was dependent on the agonist concentration; at saturating agonist concentrations (300 microM), the IC50 value was 8.19 microM, whereas at 3 microM glutamate, the IC50 value was 3.39 microM. Pb2+ was a noncompetitive inhibitor of NR1b-2A, NR1b-2C and NR1b-2D NMDA receptors. At low concentrations (<1 microM) Pb2+ potentiated NR1b-2AC NMDA receptors. These data provide further evidence to support the hypothesis that the actions of Pb2+ on NMDA receptors are determined by the receptor subunit composition.

Cloning and characterization of Kir3.1 (GIRK1) C-terminal alternative splice variants

Southern blot analysis of RT-PCR products from brain and heart revealed multiple products for a C-terminal region of Kir3.1. Sequencing yielded clones for wild-type Kir3.1 and three Kir3.1 C-terminal alternative splice variants, including a unique alternative exon. Two of these variants encoded truncated Kir3.1 molecules. Tissue distribution and electrophysiological characterization of a single truncated variant, Kir3.1(00) were then examined. Kir3.1 channels are gated by G-protein beta gamma-subunits binding to the C-terminal domain, thus, the truncation of Kir3.1(00) removes a major functional domain. When incorporated into heteromeric channels with other family members (Kir3.1, 3.2 or 3.4) several functional changes were observed: (1) Kir3.1(00) changes G-protein activation of Kir3 channels; (2) Kir3.1(00) is restricted in its ability to assemble with other channel subunits as heteromers; and (3) incorporation of Kir3.1(00) into heteromeric channel complexes alters the kinetics of channel re-activation.

The sensitivity of N-methyl-D-aspartate receptors to lead inhibition is dependent on the receptor subunit composition

Pb+2 is a potent inhibitor of N-methyl-D-aspartate (NMDA) receptors and its action is dependent on neuronal maturation. Developmentally regulated expression of NMDA receptor subunits may underlie the changing sensitivity to Pb+2. In oocytes expressing in vitro transcribed cRNAs for zeta 1 epsilon 1 or zeta 1 epsilon 2 NMDA receptor subunits, Pb+2 inhibited glutamate-activated currents with IC50 values of 0.87 +/- 0.25 and 1.21 +/- 0.22 microM, respectively, and NMDA-activated currents with IC50 values of 1.37 +/- 0.47 and 1.11 +/- 0.33 microM, respectively. In oocytes expressing zeta 1 epsilon 1 epsilon 2 subunits, the IC50 values for Pb+2 blockade of NMDA- or glutamate-activated currents were significantly larger when compared to zeta 1 epsilon 1 or zeta 1 epsilon 2 combinations. Pb+2 concentrations greater than 1 microM inhibited glutamate-activated currents with an IC50 of 6.1 +/- 1.22 microM and NMDA-activated currents with an IC50 of 6.64 +/- 3.34 microM. Pb+2 reduced the maximal current amplitude consistent with a noncompetitive block. zeta 1 epsilon 1 epsilon 2 NMDA receptors were potentiated by low concentrations of Pb+2 ( < 1.0 microM). These data suggest that brain regions with zeta 1 epsilon 1 or zeta 1 epsilon 2 NMDA receptors subunits would be more vulnerable to Pb+2 toxicity than those with zeta 1 epsilon 1 epsilon 2 NMDA-receptors, which are expressed later in development. These data provide a mechanism for the reported changes in the efficacy of block of NMDA receptors by Pb+2 during development.

Melatonin receptors activate heteromeric G-protein coupled Kir3 channels

The effects of melatonin on circadian pacemaker activity in the central nervous system may be the result of melatonin receptor activation of G-protein coupled potassium channels which inhibit the action potential firing of neurons. Xenopus laevis and human1a melatonin receptors stimulated heteromeric G-protein activated inwardly rectifying potassium channels (Kir3.1/Kir3.2) when expressed in vitro in oocytes. Pertussis toxin reduced iodo-melatonin (87.1% reduction) and melatonin (90.3% reduction) stimulated currents in a time-dependent manner for cells expressing X. laevis receptors. A similar pertussis toxin inhibition was observed for human melatonin receptors (melatonin, 78.9% reduction). This suggests a potential role for heteromeric Kir3 channels in the receptor-mediated actions of melatonin in vivo.

Residents' performance before and after night call as evaluated by an indicator of creative thought

The effects of sleep deprivation on medical personnel have received much attention. This study evaluates the effects of sleep loss on divergent-thinking (creative or innovative) processes as measured by the Torrance Test of Creative Thinking (TTCT). Anesthesia residents who had approximately 30 minutes sleep while being on-call were evaluated. These physicians had similar caffeine and nicotine consumption before and after the test. The results reported here demonstrate that postcall residents had TTCT scores that were appreciably below those scores of rested residents. Postcall verbal fluency was less among the on-call group than among the rested group (94.0 +/- 9.7 vs 101.8 +/- 9.8) as was figural originality (89.9 +/- 22.1 vs 113.3 +/- 20.3). These study results suggest that sleep deprivation affects divergent, or creative, thinking. Divergent-thinking processes are usually innovative and are used during complex problem-solving tasks. Further studies are needed on the effects of sleep deprivation. This information can then be used to help improve residents' working conditions and patient care.

Melatonin activates an outward current and inhibits Ih in rat suprachiasmatic nucleus neurons

Whole-cell voltage-clamp recordings were made from suprachiasmatic nucleus (SCN) neurons maintained in horizontal brain slices. The majority of neurons exhibited spontaneous and evoked excitatory and inhibitory synaptic currents (EPSC and IPSC), mediated by glutamate and GABA respectively. Melatonin had no effect on either the spontaneous or evoked EPSC or IPSC. Application of melatonin (0.1-30 microM) during circadian time (CT) 9-12 activated an outward current at -60 mV and increased the membrane conductance in a concentration-dependent manner. The current was augmented by depolarization, reduced by hyperpolarization and, in some cells, reversed its polarity near the potassium equilibrium potential. Some neurons also responded to melatonin during other times of the circadian day (CT 3-9 or CT 12-15). Hyperpolarizing steps, in a portion of cells, activated an inward cation current which resembled the Ih described in other neurons. Melatonin (10 microM) inhibited activation of the Ih. These data indicate that melatonin may inhibit SCN neurons by activating a potassium current and inhibiting the Ih.

A study of the responsibilities of chief residents in anesthesiology with a suggested job description

We requested information concerning the job description for the chief resident in anesthesiology from 50 different programs. Thirty-two responses were returned, with 9 responses that no such job description existed at their institutions. Eighteen of the remaining 23 respondents had a written job description for the position. Considerable variation existed in the various aspects of the position among institutions. Differences were found in the selection process, administrative duties, number of committee memberships, and educational responsibilities. We present a suggested description of the responsibilities for a chief resident in anesthesiology.

Listeriolysin O is a target of the immune response to Listeria monocytogenes

The immunologic mechanism of protective immunity to the intracellular parasite Listeria monocytogenes (Lm) is not well understood, however, antilisterial immunity can be adoptively transferred with T lymphocytes from Lm-immune donors. The Lm-immune cells are believed to produce macrophage-activating lymphokines, which leads to the eventual macrophage-dependent eradication of the bacterium. Increasing evidence suggests that immunity to Lm resides exclusively within the CD8+ T cell subset. It is possible that the Lm-immune CD8+ T cells function to release sequestered Lm from nonprofessional phagocytes to awaiting activated macrophage populations. This study was conducted to determine if listeriolysin O (LLO), which is an essential determinant of Lm pathogenicity, is also a target of the antilisterial immune response. We have found that target cells infected with a LLO+ Lm strain are lysed by Lm-immune cytotoxic cells, whereas target cells infected with a LLO- Lm mutant, or pulsed with a heat-killed Lm preparation, are not lysed by the Lm-immune effector cells. We have used a Bacillus subtilis (Bs) construct that expresses the LLO gene product and found that target cells infected with the LLO+ Bs construct are lysed by antilisterial cytotoxic cells. The antilisterial cytotoxic response is targeted against LLO, in that we have also used a Bs construct that expresses the perfringolysin (PLO) gene product and found that target cells infected with the PLO+ Bs are not lysed by antilisterial cytotoxic effector cells. These data strongly suggest that LLO is a target antigen of antilisterial immunity and may represent the dominant target during the expression of the immune response to Lm.

Typhoid fever, ciprofloxacin, and renal failure

An 11 year old boy from whom Salmonella typhi had been isolated was treated with ciprofloxacin. He developed non-oliguric acute renal failure that was treated successfully.

Dilemmas associated with antenatally detected urinary tract abnormalities

Over a five year period 55 fetuses had abnormalities of the urinary tract detected by antenatal ultrasound scan. The incidence was 1:935 total births during a one year prospective study. Intrauterine intervention was undertaken in five for suspected obstructive uropathy, which was confirmed in only two. Of 51 live born infants, five died (two with renal failure), and only 18 (35%) had a clinically detectable abnormality at birth. Twenty seven patients underwent postnatal operations, the remainder being treated conservatively. Antenatal counseling was seldom undertaken by those responsible for the postnatal care. There were many instances of prospective parents receiving little or inappropriate information. Greater cooperation is required between all the staff concerned particularly as the natural history and appropriate postnatal management of some urinary tract abnormalities are still not known.

Cutaneous host defense in leishmaniasis: interaction of isolated dermal macrophages and epidermal Langerhans cells with the insect-stage promastigote

Leishmania species are obligate intracellular pathogens of mononuclear phagocytes. Successful infection depends on sequestration of the promastigote (insect form) within host cells, allowing transformation into the relatively hardy amastigote stage. Promastigotes are killed readily by circulating phagocytes and nonimmune serum, suggesting that cutaneous infection is initiated within a permissive cell in the epidermis or dermis. From large sections of primate skin dermal macrophages and epidermal Langerhans cells were isolated, and their interaction with promastigotes of Leishmania major was investigated in vitro. Dermal macrophages were readily infected with promastigotes, and successful transformation to and replication of amastigotes was observed. Ingestion of promastigotes by dermal macrophages was not associated with a significant respiratory burst, in contrast to that by other macrophage populations, and was associated with significantly greater survival of parasites. Stimulation of these cells with phorbol myristate acetate or opsonized zymosan revealed that those cells were generally oxidatively deficient. Langerhans cells could not be successfully infected by promastigotes under similar conditions. Examination of these cells for expression of CR3, which has been identified as a potential Leishmania receptor, revealed that Langerhans cells did not express the alpha M subunit of CR3, whereas dermal macrophages were CR3 positive. These data support the concept that dermal macrophages are the site of initiation of Leishmania infection.

Loss of granule myeloperoxidase during in vitro culture of human monocytes correlates with decay in antiprotozoa activity

Human monocytes maintained in culture lose microbicidal activity against intracellular protozoa which has been correlated with attenuation of the respiratory burst. The granule enzyme myeloperoxidase, which can markedly amplify hydrogen peroxide-dependent antimicrobial activity, is also lost in vitro. Adherent monocytes were examined immediately, 3 and 10-14 days following explantation, for the magnitude of the stimulated respiratory burst and for cellular myeloperoxidase. Fresh cells generated 254 +/- 38 nmol O2-/mg protein as compared to a peak of 782 +/- 45 nmol O2-/mg at 3 days and less than 100 nmol O2-/mg after 10-14 days. The myeloperoxidase content of the cells also decreased; over 85% was lost after 3 days. Fresh monocytes killed over 90% of ingested Toxoplasma gondii or Leishmania major. In contrast, 10-14 day explanted monocytes killed only 12% of ingested Toxoplasma and 33% of Leishmania, and surviving organisms replicated readily. The 3-day monocytes were significantly less able to kill protozoa than were fresh cells despite their nearly 3-fold greater generation of O2-. If peroxidase was reintroduced into 3-day monocytes by coating organisms with eosinophil peroxidase prior to phagocytosis, their antiprotozoa activity was nearly restored to that of freshly explanted cells.

Renal vein renin measurement and arteriography in the investigation and management of severe childhood hypertension

Forty-two children aged one to sixteen years with persistent and severe hypertension were investigated by renal vein renin measurements. There were no serious complications in the 49 procedures performed and technical failure occurred on three occasions. Arteriography was performed in 35. Asymmetrical renin release was found in 22 patients and of these 15 underwent surgery. This was successful in 12 patients (80%) who became normotensive. Ten had unilateral disease (100% cure rate) but only 2 (40%) with bilateral disease became normotensive. Renal vein renin studies combined with arteriography have a useful role in the investigation and management of childhood hypertension.

Angiotensin II in essential hypertension

Plasma concentrations of angiotensin II (PAC) were measured in a group of 146 hypertensive patients (diastolic pressure greater than 105 mm Hg) who had no apparent underlying cause for their condition and 113 randomly selected normotensive controls (diastolic pressure less than 90 mm Hg). There was no evidence of bimodality in the frequency distribution curves for plasma angiotensin II concentrations among the hypertensive patients. It was concluded that hypertension associated with low angiotensin II concentration and by implication "low-renin" hypertension is not a condition separate from essential hypertension.

A blood pressure clinic in a health centre

Following a screening survey for hypertension in Renfrew, a blood pressure clinic was established in a health centre. Three hospital doctors, each working an average of two sessions weekly, saw 368 patients. A specially trained nurse played an important part in the running of the clinic. Attendance of patients was high, and defaulting amongst those needing treatment was low. Blood pressures were well controlled in 75% of the patients. The clinic has proved an acceptable method of managing large numbers of hypertensives without reference to hospital.

Cardiac and pulmonary fat embolectomy for suspected fat embolus

Nelson, C. S. (1974).Thorax, 29, 134-137. Cardiac and pulmonary fat embolectomy for suspected fat embolus. There is no specific treatment of fat embolism, whether the embolism is predominantly cerebral, pulmonary, renal or mesenteric.

A 46-year-old man had fractured his right femur for the third time in December 1971. Seventy hours later he suddenly developed the cardiovascular, respiratory, and cerebral manifestations of post-traumatic fat embolism. His chest radiograph at the onset of symptoms was consistent with fat embolism. He underwent cardiac and pulmonary embolectomy on 7 December 1971 and made a most dramatic recovery. His haemobronchorrhoea, dyspnoea, tachypnoea, hyperpyrexia, and profound shock disappeared at the end of the operation. His only postoperative cerebral disturbance was mild disorientation.

The pathophysiological changes accompanying fat embolism are due to toxic vasculitis and fat macroglobule aggregations blockading the pulmonary arterioles and capillaries. The blockading concept is the basis for cardiac and pulmonary fat embolectomy. Only a larger series embodying a multicentre trial will show whether or not cardiopulmonary fat embolectomy is a specific treatment of massive fat embolism.

The purpose of this paper is to report on the technique and result of embolectomy for a suspected fat embolus following fracture of the femur.