Effects of the beta(2)-agonist clenbuterol on respiratory and limb muscles of weaning rats

The aim of this study was to analyze the effects of chronic administration of the beta(2)-agonist clenbuterol (1.5 mg x kg(-1) x day(-1) for 4 wk in the drinking water) on respiratory (diaphragm and parasternal intercostal) and hindlimb (tibialis and soleus) muscles in young rats during postnatal development (21 to 49 postnatal days). The treatment resulted in very little stimulation of muscle growth. Significant slow-to-fast transitions in the expression of myosin heavy chain isoforms and significant increases in the myofibrillar ATPase activity were found in the diaphragm and soleus, whereas tibialis anterior and intercostal muscles did not show any significant fiber-type alteration. Decrease of oxidative enzyme activities and increase of glycolytic enzyme activities were also observed. It is concluded that whereas the growth stimulation is age dependent and only detectable in adult rats, the fiber-type transformation is also present in weaning rats and particularly evident in the soleus and diaphragm. The fiber-type transformation caused by clenbuterol might lead to an enhancement of contractile performance and also to a reduced resistance to fatigue.     

Adaptive responses of human monocytes infected by bordetella pertussis: the role of adenylate cyclase hemolysin

The activation/adaptive responses of human monocytes exposed to Bordetella pertussis parental or mutant strains were evaluated and correlated to the expression of two bacterial toxins: adenylate cyclase-hemolysin and pertussis toxin. The marked rise in intracellular cyclic adenosine monophosphate (cAMP) observed in monocytes infected by B. pertussis parental strain, inversely correlated with (1) the production of tumor necrosis factor alpha; (2) the release of superoxide anion; and (3) the expression of the 72-kDa heat shock/stress protein, Hsp70. Experiments performed with mutants deficient in adenylate cyclase-hemolysin or with purified bacterial toxins confirmed the key role of adenylate cyclase-hemolysin in the control of monocytes' response to infection by B. pertussis. This bacterial strategy primarily involves evasion from antimicrobial defenses and, eventually, the sacrifice of the host cell.     

Curosurf modulates cAMP accumulation in human monocytes through a membrane-controlled mechanism

The cellular mechanisms by which pulmonary surfactant exerts its effects, including anti-inflammatory or proinflammatory effects, have remained elusive. To address the issue of whether plasma membrane modifications represent a target for these mechanisms, we designed an experimental protocol involving the determination of changes in cAMP levels under membrane-dependent or -independent stimulatory pathways. The effects of a modified natural porcine surfactant, Curosurf, and the major surfactant protein A were evaluated on resting and stimulated cAMP levels of human monocytes. We found that agents that elevate intracellular cAMP exhibit different susceptibilities toward a preexposure to Curosurf. The rise in cAMP induced by membrane-active agents such as cholera toxin or the diterpene forskolin was significantly inhibited by monocyte preexposure to Curosurf. In contrast, the rise in cAMP induced by the membrane-permeant phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine or by the Bordetella pertussis toxin adenylate cyclase-hemolysin was unaffected by Curosurf. Surfactant protein A did not affect either cAMP levels or the inhibitory capacity of Curosurf. We suggest that a plasma membrane-associated event affecting the mechanism underlying the effects of cholera toxin or forskolin is involved in the inhibition of cAMP accumulation caused by Curosurf.     

Mammalian CLASP1 and CLASP2 cooperate to ensure mitotic fidelity by regulating spindle and kinetochore function

CLASPs are widely conserved microtubule plus-end-tracking proteins with essential roles in the local regulation of microtubule dynamics. In yeast, Drosophila, and Xenopus, a single CLASP orthologue is present, which is required for mitotic spindle assembly by regulating microtubule dynamics at the kinetochore. In mammals, however, only CLASP1 has been directly implicated in cell division, despite the existence of a second paralogue, CLASP2, whose mitotic roles remain unknown. Here, we show that CLASP2 localization at kinetochores, centrosomes, and spindle throughout mitosis is remarkably similar to CLASP1, both showing fast microtubule-independent turnover rates. Strikingly, primary fibroblasts from Clasp2 knockout mice show numerous spindle and chromosome segregation defects that can be partially rescued by ectopic expression of Clasp1 or Clasp2. Moreover, chromosome segregation rates during anaphase A and B are slower in Clasp2 knockout cells, which is consistent with a role of CLASP2 in the regulation of kinetochore and spindle function. Noteworthy, cell viability/proliferation and spindle checkpoint function were not impaired in Clasp2 knockout cells, but the fidelity of mitosis was strongly compromised, leading to severe chromosomal instability in adult cells. Together, our data support that the partial redundancy of CLASPs during mitosis acts as a possible mechanism to prevent aneuploidy in mammals.     

Acidification of Soil in a Dry Land Winter Wheat-sorghum/corn-fallow Rotation in the Semiarid U.S. Great Plains

Soil pH is decreasing in many soils in the semiarid Great Plains of the United States under dry land no-till (NT) cropping systems. This study was conducted to determine the rate of acidification and the causes of the acidification of a soil cropped to a winter wheat (Triticum aestivum L.)-grain sorghum [Sorghum bicolor (L.) Moench]/corn (Zea mays L.)-fallow rotation (W-S/C-F) under NT. The study was conducted from 1989 to 2003 on soil with a long-term history of either continuous NT management [NT(LT)] (1962–2003) or conventional tillage (CT) (1962–1988) then converted to NT [NT(C)] (1989–2003). Nitrogen was applied as ammonium nitrate (AN) at a rate of 23 kg N ha⁻¹ in 1989 and as urea ammonium nitrate (UAN) at an average annual rate of 50 kg N ha⁻¹ from 1990 to 2003 for both NT treatments. Soil samples were collected at depth increments of 0–5, 5–10, 10–15, and 15–30 cm in the spring of 1989 and 2003. Acidification rates for the NT(LT) and NT(C) treatments were 1.13 and 1.48 kmol H⁺ ha⁻¹ yr⁻¹ in the 0–30 cm depth, respectively. The amount of CaCO₃ needed to neutralize the acidification is 57 and 74 kg ha⁻¹ yr⁻¹ for the NT(LT) and NT(C) treatments, respectively. A proton budget estimated by the Helyar and Porter [1989, Soil Acidity and Plant Growth, Academic Press] method indicated that NO₃⁻ leaching from the 30 cm depth was a primary cause of long-term acidification in this soil. Nitrate leaching accounted for 59 and 66% of the H⁺ from the acid causing factors for NT(LT) and NT(C) treatments, respectively. The addition of crop residues to the soil neutralized 62 and 47% of the acidity produced from the leaching of NO₃⁻, and 37 and 31% of the acid resulting from NO₃⁻ leaching and the other acid-causing constituents for the NT(LT) and NT(C) treatments, respectively. These results document that surface soils in dry land W-S/C-F rotations under NT are acidifying under current management practices. Improved management to increase nitrogen uptake efficiency from applied fertilizer would help reduce the rate of acidification. The addition of lime materials to prevent negative impacts on grain yields may be necessary in the future under current management practices. A contribution of the university of Nebraska Agricultural Research Division, Lincoln, NE 68583. Journal series No. 15120     

Toxicity of cadmium in tobacco smoke: protection by antioxidants and chelating resins

The effects of cadmium, an environmental toxin present in tobacco smoke, were studied in vitro in human monocytes and compared to those of tobacco smoke. Overexpression of the 72 λkDa heat shock/stress protein Hsp70 and cell death occurred with a similar time-course and to a similar extent in human monocytes exposed to either cadmium or tobacco smoke. Cadmium and tobacco smoke-mediated toxicity were associated with a decrease in the cellular content of glutathione and ATP and the glutathione precursor N -acetyl- l -cysteine prevented both cadmium and tobacco smoke-mediated toxicity. Furthermore, tobacco smoke-mediated toxicity was prevented by pretreatment with the cadmium chelator resin Chelex-100, supporting the conclusion that cadmium plays a major role in tobacco smoke-mediated toxicity.     

Heat shock proteins chaperoning life and death

No Abstract Available