Lowering pH in blood platelets dissociates myosin phosphorylation from shape change and myosin association with the cytoskeleton

Platelet shape change induced by ADP is relatively independent of external pH over the range 6-7. If the chloride ion in the buffer is replaced by weak acids, however, shape change is rapidly and reversibly inhibited as a function of lowered pH (92% at pH 6.0). This inhibition is correlated with lowered internal pH caused by the weak acids, as measured by the 5,5-dimethyloxazolidine 2,4-dione technique. Shape change was 50% inhibited at internal pH 6.4 when 50 mM NaCl was replaced by propionate (PR). When platelets were stimulated with ADP 10-20 s after addition of PR to a final pH of 6 (PR6), both myosin light chain (MLC) phosphorylation and myosin and actin association with the cytoskeleton were reduced in correlation with the inhibition of shape change. But when ADP was added 30 s after PR6, the MLC phosphorylation was essentially the same in PR or in chloride, although shape change and myosin and actin association with the cytoskeleton remained inhibited. This was shown to be due mainly to endogenous phosphorylation of MLC. On return to neutral pH, platelets in PR immediately changed shape and myosin and actin became associated with the cytoskeleton. Two-dimensional tryptic peptides of MLC showed two major spots after PR6 treatment, indicating that both the MLC kinase site and the protein kinase C sites were phosphorylated. The results show that increased internal pH is not required for shape change, although it may affect the rate. In PR6, as after phorbol esters, MLC phosphorylation can be uncoupled from shape change. The association of myosin and actin with the cytoskeleton is closely correlated with shape change, suggesting that shape change requires the active interaction of these contractile proteins.     

Discriminative stimulus properties of the serotonin agonist 1-(3-trifluoromethylphenyl)piperazine (TFMPP)

Using a standard two-lever drug discrimination procedure, twelve rats were trained to discriminate 1.0 mg/kg of the serotonin (5-HT) agonist TFMPP from saline. Once trained, the animals displayed a dose-related decrease in discriminative performance upon administration of lower doses of TFMPP. Tests of stimulus generalization were performed using the purported 5-HT agonist RU-24, 969 and 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM). While TFMPP produced stimulus effects similar to those of RU-24,969, these effects seem to be dissimilar to those of DOM. The results of the present study suggest that the discriminative stimulus effects of TFMPP may involve a 5-HT1-related mechanism.     

Hallucinogens as a discriminative stimuli: generalization of DOM to a 5-methoxy-N, N-dimethyltryptamine stimulus.

Hallucinogens (psychotomimetic agents) are capable of producing various discriminative stimuli for animals. Serotonergic involvement has been implicated as playing a role in the behavioral effects elicited by, for example, mescaline and DOM. Because certain tryptamine analogs possess high serotonin (5-HT) receptor binding affinities, it was of interest to examine one of the more potent agents. Employing a standard operant test chamber, six rats were trained to respond under a variable-interval 15-second schedule of sweetened-milk reinforcement. 5-Methoxy-N, N-dimethyltryptamine (5-OMe DMT), which possesses a 5-HT receptor affinity much higher than that of mescaline, but nearly equivalent to that of DOM, was found to serve as a discriminative stimulus. Furthermore, the 5-OMe DMT stimulus could be attenuated by the 5-HT antagonist BC-105. The 5-OMe DMT stimulus generalized with DOM suggesting that these two hallucinogens produce qualitatively similar interoceptive cues in rats.     

Stretch increases inositol trisphosphate and inositol tetrakisphosphate in cultured pulmonary vascular smooth muscle cells.

There are no reports of the effect of stretch on inositol phosphates in smooth muscle. Phosphoinositide and inositol phosphate metabolism was studied in cultured rat vascular smooth muscle cells subjected to stretching. The masses of inositol trisphosphate and tetrakisphosphate increased (+34 +/- 7% and +58 +/- 12%, respectively; p less than 0.001) after 25 s of a single 20% stretch and had returned to control levels by 45 s; phosphatidylinositol, phosphatidylinositol phosphate and bisphosphate did not change. Repetitive stretch did not alter the masses of any of the compounds. A single stretch also increased 45Ca2+ efflux (+52 +/- 5%, p less than 0.01). These data suggest that stretch of cultured vascular smooth muscle can elicit a rapid, short-lived increase in inositol phosphates, which may subsequently affect Ca2+.     

Development of cell surface saccharides on embryonic pancreatic cells

Using a battery of seven lectin-ferritin conjugates as probes for cell surface glycoconjugates, we have studied the pattern of plasmalemmal differentiation of cells in the embryonic rat pancreas from day 15 in utero to the early postpartum stage. Our results indicate that differentiation of plasmalemmal glycoconjugates on acinar, endocrine, and centroacinar cells is temporally correlated with development and is unique for each cell type, as indicated by lectin-ferritin binding. Specifically, (a) expression of adult cell surface saccharide phenotype can be detected on presumptive acinar cells as early as 15 d in utero, as indicated by soybean agglutinin binding, and precedes development of intracellular organelles characteristic of mature acinar cells; (b) maturation of the plasmalemma of acinar cells is reached after intracellular cytodifferentiation is completed, as indicated by appearance of Con A and fucoselectin binding sites only at day 19 of development; conversely, maturation of the endocrine cell plasmalemma is accompanied by "loss" (masking) of ricinus communis II agglutinin receptors; and (c) binding sites for fucose lectins and for soybean agglutinin are absent on endocrine and centroacinar cells at all stages examined. We conclude that acinar, centroacinar, and endocrine cells develop from a common progenitor cell(s) whose plasmalemmal carbohydrate composition resembles most closely that of the adult centroacinar cell. Finally, appearance of acinar lumina beginning at approximately 17 d in utero is accompanied by differenetiation of apical and basolateral plasmalemmal domains of epithelial cells, as indicated by enhanced binding of several lectin-ferritin conjugates to the apical plasmalemmal, a pattern that persists from this stage through adult life.     

Age-Specific Mortality During the 1918 Influenza Pandemic: Unravelling the Mystery of High Young Adult Mortality

The worldwide spread of a novel influenza A (H1N1) virus in 2009 showed that influenza remains a significant health threat, even for individuals in the prime of life. This paper focuses on the unusually high young adult mortality observed during the Spanish flu pandemic of 1918. Using historical records from Canada and the U.S., we report a peak of mortality at the exact age of 28 during the pandemic and argue that this increased mortality resulted from an early life exposure to influenza during the previous Russian flu pandemic of 1889–90. We posit that in specific instances, development of immunological memory to an influenza virus strain in early life may lead to a dysregulated immune response to antigenically novel strains encountered in later life, thereby increasing the risk of death. Exposure during critical periods of development could also create holes in the T cell repertoire and impair fetal maturation in general, thereby increasing mortality from infectious diseases later in life. Knowledge of the age-pattern of susceptibility to mortality from influenza could improve crisis management during future influenza pandemics.

“The war is over – and I must go” Egon Schiele, 1890–1918.

     

Process model comparison and transferability across bioreactor scales and modes of operation for a mammalian cell bioprocess

A Monod kinetic model, logistic equation model, and statistical regression model were developed for a Chinese hamster ovary cell bioprocess operated under three different modes of operation (batch, bolus fed‐batch, and continuous fed‐batch) and grown on two different bioreactor scales (3 L bench‐top and 15 L pilot‐scale). The Monod kinetic model was developed for all modes of operation under study and predicted cell density, glucose glutamine, lactate, and ammonia concentrations well for the bioprocess. However, it was computationally demanding due to the large number of parameters necessary to produce a good model fit. The transferability of the Monod kinetic model structure and parameter set across bioreactor scales and modes of operation was investigated and a parameter sensitivity analysis performed. The experimentally determined parameters had the greatest influence on model performance. They changed with scale and mode of operation, but were easily calculated. The remaining parameters, which were fitted using a differential evolutionary algorithm, were not as crucial. Logistic equation and statistical regression models were investigated as alternatives to the Monod kinetic model. They were less computationally intensive to develop due to the absence of a large parameter set. However, modeling of the nutrient and metabolite concentrations proved to be troublesome due to the logistic equation model structure and the inability of both models to incorporate a feed. The complexity, computational load, and effort required for model development has to be balanced with the necessary level of model sophistication when choosing which model type to develop for a particular application. © 2012 American Institute of Chemical Engineers Biotechnol. Prog., 2013     

Alterations in Phosphorylation of Hepatocyte Ribosomal Protein S6 Control Plasmodium Liver Stage Infection

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Oxygen mass transfer characteristics in a membrane-aerated biofilm reactor

Immobilization of pollutant-degrading microorganisms on oxygen-permeable membranes provides a novel method of increasing the oxidation capacity of wastewater treatment bioreactors. Oxygen mass transfer characteristics during continuous-flow steady-state experiments were investigated for biofilms supported on tubular silicone membranes. An analysis of oxygen mass transport and reaction using an established mathematical model for dual-substrate limitation supported the experimental results reported. In thick biofilms, an active layer of biomass where both carbon substrate and oxygen are available was found to exist. The location of this active layer varies depending on the ratio of the carbon substrate loading rate to the intramembrane oxygen pressure. The thickness of a carbon-substrate-starved layer was found to greatly influence the mass transport of oxygen into the active biomass layer, which was located close to, but not in contact with, the biofilm-liquid interface. The experimental results demonstrated that oxygen uptake rates as high as 20 g m-2 d-1 bar-1 can be achieved, and the model predicts that, for an optimized biofilm thickness, oxygen uptake rates of more than 30 g m-2 d-1 bar-1 should be possible. This would allow membrane-aerated biofilm reactors to operate with much greater thicknesses of active biomass than can conventional biofilm reactors as well as offering the further advantage of close to 100% oxygen conversion efficiencies for the treatment of high-strength wastewaters. In the case of dual- substrate-limited biofilms, the potential to increase the oxygen flux does not necessarily increase the substrate (acetate) removal rate.