Quantification of malaria parasite release from infected erythrocytes: inhibition by protein-free media

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Hardly vacuous: The parasitophorous vacuolar membrane of malaria parasites

When a malaria parasite invades a host erythrocyte it pushes itself in and invaginates a portion of the host membrane, thereby sealing itself inside and establishing itself in the resulting vacuole. The parasitophorous vacuolar membrane (PVM) that surrounds the parasite is modified by the parasite, using its secretory organelles. To survive within this enveloping membrane, the organism must take in nutrients, secrete wastes, export proteins into the host cell, and eventually egress. Here, we review current understanding of the unique solutions Plasmodium has evolved to these challenges and discuss the remaining questions

Comparison of Two Rodent Models of Maternal Separation on Juvenile Social Behavior

Early childhood deprivation is associated with an increased risk of attachment disorders and psychopathology. The neural consequences of exposure to stress early in life have used two major rodent models to provide important tools for translational research. Although both models have been termed maternal separation (MS), the paradigms differ in ways that clearly shift the focus of stress between maternal and offspring units. The first model, here called early deprivation (ED), isolates pups individually while the dam is left not alone, but with a subset of littermates in the home nest (“stay-at-homes”). The other model, here called MS, isolates the dam in a novel cage while the pups are separated together. In this study, these two early stress models were directly compared for their effects on social behaviors in male and female juvenile offspring. Although both models altered play behavior compared to controls, patterns of prosocial behaviors versus submissive behaviors differed by model and sex. Additionally, there were main effects of sex, with female ED subjects exhibited masculinizing effects of early stress during play sessions. Maternal behavior upon reunion with the isolated subjects was significantly increased in the MS condition compared to both ED and control conditions, which also differed but by a lesser magnitude. “stay-at-homes” were tested since some laboratories use them for controls rather than undisturbed litters; they displayed significantly different sex-dependent play compared to undisturbed subjects. These results indicate that early stress effects vary by paradigm of separation. We suggest that MS produces greater stress on the dam and thus greater maternal mediation, while ED causes greater stress on the neonates, resulting in different behavioral sequela that warrant attention when using these models for translational research

Osmotic forces are not critical for Ca 2+ -induced secretion from permeabilized human neutrophils

In order to examine the role of osmotic forces in degranulation, the effects of solutes and osmolality on granule secretion were explored using both FMLP-stimulated, intact neutrophils and Ca 2+ -stimulated, permeabilized cells. We employed a HEPES-based buffer system which was supplemented with: (a) permeant (KCl or NaCI) or impermeant (Na-isethionate or choline-CI) ions, or (b) permeant (urea) or impermeant (sucrose) uncharged solutes. Intact and permeabilized cells had significantly different solute requirements for degranulation. FMLP-stimulated release from intact cells was supported by NaCI or Na-isethionate > KCl > choline-Cl or sucrose > urea. In contrast, the rank order of Ca 2+ -stimulated release from permeabilized cells was choline-C > Na-isethionate, KCl, or NaCl > sucrose > urea. Hypo-osmotic conditions caused increased levels of background granule release from both intact and permeabilized neutrophils. However, hypo-osmolality inhibited both FMLP-stimulated degranulation from intact cells and Ca 2+ -induced release from permeabilized neutrophils. While hyperosmotic conditions inhibited stimulated release from intact cells, this inhibition was much less pronounced in permeabilized cells when the granules were directly exposed to these solutions. In fact, hyperosmotic sucrose greatly enhanced Ca 2+ -induced secretion. Although isolated specific and azurophil granules showed some lytic tendencies in hypo-osmotic buffers, the overall stability of the isolated granules did not indicate that swelling alone could effect degranulation. These results suggest that degranulation in permeabilized cells is neither due to nor driven by simple osmotic forces (under resting or stimulated conditions) and emphasize differences obtained by bathing both the granules and plasma membrane (as opposed to membranes alone) in various solutes.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/49877/1/1041350204_ftp.pd

“Entropic Traps” in the Kinetics of Phase Separation in Multicomponent Membranes Stabilize Nanodomains

AbstractWe quantitatively describe the creation and evolution of phase-separated domains in a multicomponent lipid bilayer membrane. The early stages, termed the nucleation stage and the independent growth stage, are extremely rapid (characteristic times are submillisecond and millisecond, respectively) and the system consists of nanodomains of average radius ∼5–50nm. Next, mobility of domains becomes consequential; domain merger and fission become the dominant mechanisms of matter exchange, and line tension γ is the main determinant of the domain size distribution at any point in time. For sufficiently small γ, the decrease in the entropy term that results from domain merger is larger than the decrease in boundary energy, and only nanodomains are present. For large γ, the decrease in boundary energy dominates the unfavorable entropy of merger, and merger leads to rapid enlargement of nanodomains to radii of micrometer scale. At intermediate line tensions and within finite times, nanodomains can remain dispersed and coexist with a new global phase. The theoretical critical value of line tension needed to rapidly form large rafts is in accord with the experimental estimate from the curvatures of budding domains in giant unilamellar vesicles

Long, Saturated Chains: Tasty Domains for Kinases of Insulin Resistance

The mechanistic basis of how cells respond to increased fatty acids (FAs) is murky but potentially involves receptor-mediated activation or inhibition by different FA classes. Holzer et al. (2011) recently propose in Cell that expansion of intracellular membrane microdomains induced by saturated FA recruit and activate c-Src for JNK activation

Isolation and ultrastructural characterization of squid synaptic vesicles

Author Posting. © Marine Biological Laboratory, 2011. This article is posted here by permission of Marine Biological Laboratory for personal use, not for redistribution. The definitive version was published in Biological Bulletin 220 (2011): 89-96.Synaptic vesicles contain a variety of proteins and lipids that mediate fusion with the pre-synaptic membrane. Although the structures of many synaptic vesicle proteins are known, an overall picture of how they are organized at the vesicle surface is lacking. In this paper, we describe a better method for the isolation of squid synaptic vesicles and characterize the results. For highly pure and intact synaptic vesicles from squid optic lobe, glycerol density gradient centrifugation was the key step. Different electron microscopic methods show that vesicle membrane surfaces are largely covered with structures corresponding to surface proteins. Each vesicle contains several stalked globular structures that extend from the vesicle surface and are consistent with the V-ATPase. BLAST search of a library of squid expressed sequence tags identifies 10 V-ATPase subunits, which are expressed in the squid stellate ganglia. Negative-stain tomography demonstrates directly that vesicles flatten during the drying step of negative staining, and furthermore shows details of individual vesicles and other proteins at the vesicle surface.JAD is supported by the RI-INBRE program award # P20RR016457-10 from the National Center for Research Resources (NCRR), NIH