Galphai is not required for chemotaxis mediated by Gi-coupled receptors

Pertussis toxin inhibits chemotaxis of neutrophils by preventing chemoattractant receptors from activating trimeric G proteins in the Gi subfamily. In HEK293 cells expressing recombinant receptors, directional migration toward appropriate agonist ligands requires release of free G protein betagamma subunits and can be triggered by agonists for receptors coupled to Gi but not by agonists for receptors coupled to two other G proteins, Gs and Gq. Because activation of any G protein presumably releases free Gbetagamma, we tested the hypothesis that chemotaxis also requires activated alpha subunits (Galphai) of Gi proteins. HEK293 cells were stably cotransfected with the Gi-coupled receptor for interleukin-8, CXCR1, and with a chimeric Galpha, Galphaqz5, which resembles Galphai in susceptibility to activation by Gi-coupled receptors but cannot regulate the Galphai effector, adenylyl cyclase. These cells, unlike cells expressing CXCR1 alone, migrated toward interleukin-8 even after treatment with pertussis toxin, which prevents activation of endogenous Galphai but not that of Galphaqz5. We infer that chemotaxis does not require activation of Galphai. Because chemotaxis is mediated by Gbetagamma subunits released when Gi-coupled receptors activate Galphaqz5, but not when Gq- or Gs-coupled receptors activate their respective G proteins, we propose that Gi-coupled receptors transmit a necessary chemotactic signal that is independent of Galphai.     

Deep-vein thrombosis

Deep-vein thrombosis is an important complication of several inherited and acquired disorders, but may also occur spontaneously. Prevention of recurrent venous thrombosis and pulmonary embolism is the main reason for accurate diagnosis and adequate treatment. This seminar discusses only symptomatic deep-vein thrombosis. The diagnosis can be confirmed by objective tests in only about 30% of patients with symptoms. Venous thromboembolic complications happen in less than 1% of untreated patients in whom the presence of venous thrombosis is rejected on the basis of serial ultrasonography or ultrasonography plus either D-dimer or clinical score. Initial anticoagulant treatment (intravenous or subcutaneous heparin) should continue until oral anticoagulant treatment, started concurrently, increases the international normalised ratio above 2.0 for more than 24 h. The optimum duration of oral anticoagulant treatment is unresolved, but may be guided by the presence of temporary or persistent risk factors or presentation with recurrent venous thromboembolism.     

Extremely fast folding of a very stable leucine zipper with a strengthened hydrophobic core and lacking electrostatic interactions between helices

The dimer interface of a leucine zipper involves hydrophobic as well as electrostatic interactions between the component helices. Here we ask how hydrophobic effects and electrostatic repulsion balance the rate of folding and thermodynamic stability of a designed dimeric leucine zipper formed by the acidic peptide A that contains four repeating sequence units, (abcdefg)4. The aliphatic a and d residues of peptide A were the same as in the GCN4 leucine zipper but the e and g positions were occupied by Glu, which prevented folding above pH 6 because of electrostatic repulsion. Leucine zipper A2 was formed by protonation of the e and g side chains with a sharp transition midpoint at pH 5.2. Folding could be described by a two-state transition from two unfolded random coil monomers to a coiled coil dimer. There was a linear relationship between the logarithm of the rate constants and the number of repulsive charges on the folded leucine zipper dimer. The same linear relationship applied to the free energy of unfolding and the number of repulsive charges at thermodynamic equilibrium. Fully protonated peptide A folded at a near diffusion-limited rate (kon = 3 x 10(8) M-1 s-1), and the free energy of folding was -55 kJ mol-1 at 25 degrees C. The present work shows that protonation of Glu in positions e and g increases both the folding rate and the stability of the leucine zipper in the absence of any interhelical electrostatic interactions. Protonated Glu is proposed to act like a nonpolar residue and to strengthen the hydrophobic core by folding back toward the core residues in the a and d positions. This effect adds more to the free energy of unfolding and to the rate of folding than maximizing the number of salt bridges across the helix interface in an electrostatically stabilized heterodimeric leucine zipper [Wendt, H., Leder, L., H?rm?, H., Jelesarov, I., Baici, A., and Bosshard, H. R. (1997) Biochemistry 36, 204-213].     

Deformation bands, the LEDS theory, and their importance in texture development: Part I. Previous evidence and new observations

The present state of knowledge regarding “regular” deformation bands (DBs) is reviewed in the light of some recent observations on DBs in compressed polycrystalline aluminum. These are slablike volume elements within which different selections of slip systems operate, always fewer than required for homologous deformation, in opposition to the assumption that grains deform as units which are common to all, the Sachs, the Boas and Schmid, and the Taylor/Bishop and Hill models. The need for a better integration of this knowledge with not only the origin of deformation textures but also more generally with the theory of plastic deformation is pointed out.     

L-Arginine normalizes coronary vasomotion in long-term smokers

BACKGROUND: Noninvasive measurements of myocardial blood flow (MBF) with PET revealed an abnormal coronary vasomotor response to cold pressor test in healthy long-term smokers. If coronary endothelial dysfunction accounted for this abnormality, we hypothesized that it could be reversed by L-arginine as the substrate for NO synthase. METHODS AND RESULTS: MBF was quantified with 13N-labeled ammonia and PET in 11 healthy smokers (age, 45+/-10 years; 27+/-10 years of smoking) and in 12 age-matched nonsmokers on 2 separate days. On day 1, MBF was measured at rest and, after intravenous L-arginine, during cold pressor test. On day 2, MBF was measured during cold pressor test and then at rest during L-arginine. Baseline rate-pressure product (RPP) (6559+/-1590 versus 7144+/-1157 bpmxmm Hg) and MBF (0.65+/-0.14 versus 0.73+/-0.13 mL x g-1 x min-1) were similar in nonsmokers and smokers. Cold pressor test increased RPP similarly in both groups (53+/-26% versus 46+/-26%), whereas MBF increased in nonsmokers (to 0.93+/-0.25 mL x g-1 x min-1; P<0.05) but not in smokers (0.80+/-0.16 mL x g-1 x min-1). The percent MBF increase differed between nonsmokers and smokers (44+/-25% versus 11+/-14%; P=0.0017). However, after L-arginine, the magnitude of MBF response to cold pressor test no longer differed between groups (48+/-36% versus 48+/-28%), whereas RPP again increased similarly in the 2 groups (59+/-30% versus 44+/-16%). L-Arginine had no effect on resting MBF in smokers or nonsmokers. CONCLUSIONS: Our findings implicate the coronary endothelium as the major site of the abnormal vasomotor response in long-term smokers. Cold pressor test combined with PET imaging may allow the noninvasive identification of coronary endothelial dysfunction in humans.     

Single-chamber atrial pacing is better than single chamber ventricular pacing in patients with sick sinus syndrome. Results of long-term follow up in a prospective randomized study

In a study of 225 patients with sick sinus syndrome randomized to single chamber atrial pacing (n = 110) or ventricular pacing (n = 115), atrial pacing was associated with less atrial fibrillation and thromboembolism after 3.3 years follow-up. To determine whether this beneficial effect of atrial pacing is maintained at long-term, follow-up was extended. Follow-up visits were at 3 months, 12 months, and then once every year, and included physical examination, ECG, and pacemaker check-up. After 5.5 years follow-up, all-cause mortality, cardiovascular deaths, atrial fibrillation, thromboembolism, and heart failure were significantly less in the atrial group. AV block occurred in four patients in the atrial group. The beneficial effect of atrial pacing observed previously is enhanced substantially after extended follow-up. Patients with sick sinus syndrome should be treated with an atrial pacing system.     

Organ-specific metastases in immunodeficient mice injected with human melanoma cells: a quantitative pathological analysis

Pathological and morphometric techniques were used to investigate the potential of two human melanoma cell lines for organ colonization in three different immunodeficient mouse strains; nude (nu/nu), NIH triple immunodeficient (TID: nu/nu, bg/bg, xid/xid) and severe combined immunodeficient (SCID) mice. The MM-RU cell line gave rise exclusively to lung metastases, whereas the MM-AN cell line gave rise to lung and extrapulmonary metastases. Although the TID mice showed more pancreatic and brown fat lesions than nude or SCID mice, the overall pattern of distribution of organ metastases among the strains was similar, suggesting that cellular properties intrinsic to the melanoma cells are important for the colonization of specific organs. The metastatic nodules were well circumscribed in all organs and exhibited peripherally located macrophages, except for brain metastases, where a more invasive pattern along vasculature was observed. The differences in cellular infiltrate and infiltrative patterns of the tumors implicate features of the host microenvironment (organ-specific factors) which are, at least in part, independent of the host's genetic background or degree of immunodeficiency. Our findings suggest that intrinsic malignant cellular properties play an important role in organ-specific colonization by haematogenously metastasizing cells.     

Physical exertion as a trigger of acute myocardial infarction. Triggers and Mechanisms of Myocardial Infarction Study Group

BACKGROUND: It is controversial whether the onset of myocardial infarction occurs randomly or is precipitated by identifiable stimuli. Previous studies have suggested a higher risk of cardiac events in association with exertion. METHODS: Consecutive patients with acute myocardial infarction were identified by recording all admissions to our hospital in Berlin and by monitoring a general population of 330,000 residents in Augsburg, Germany. Information on the circumstances of each infarction was obtained by means of standardized interviews. The data analysis included a comparison of patients with matched controls and a case-crossover comparison (one in which each patient serves as his or her own control) of the patient's usual frequency of exertion with the last episode of exertion before the onset of myocardial infarction. RESULTS: From January 1989 through December 1991, 1194 patients (74 percent of whom were men; mean age [+/- SD], 61 +/- 9 years) completed the interview 13 +/- 6 days after infarction. We found that 7.1 percent of the case patients had engaged in physical exertion (> or = 6 metabolic equivalents) at the onset of infarction, as compared with 3.9 percent of the controls at the onset of the control event. For the patients as compared with the matched controls, the adjusted relative risk of having engaged in strenuous physical activity at the onset of infarction or the control event was 2.1 (95 percent confidence interval, 1.1 to 3.6). The case-crossover comparison yielded a similar relative risk of 2.1 (95 percent confidence interval, 1.6 to 3.1) for having engaged in strenuous physical activity within one hour before myocardial infarction. Patients whose frequency of regular exercise was less than four and four or more times per week had relative risks of 6.9 and 1.3, respectively (P < 0.01). CONCLUSIONS: A period of strenuous physical activity is associated with a temporary increase in the risk of having a myocardial infarction, particularly among patients who exercise infrequently. These findings should aid in the identification of the triggering mechanisms for myocardial infarction and improve prevention of this common and serious disorder.     

Parasellar epidural hydatid cysts

We report two rare cases of parasellar epidural hydatid cysts. Among the 64 patients with intracranial hydatid cysts we have treated in the past 20 years, only these two cases were located epidurally. Because the location and the computed tomographic characteristics were so different from the other cysts, the preoperative diagnosis was difficult to make. We were unable to remove the cysts without rupturing them because they were tightly surrounded. Both patients underwent surgery twice because of a recurrence. The treatment of this kind of case requires further discussion.