Membrane lipid order of human red blood cells is altered by physiological levels of hydrostatic pressure

Modulation of a rapid neurotransmitter receptor-ion channel by membrane lipids

Membrane lipids modulate the proteins embedded in the bilayer matrix by two non-exclusive mechanisms: direct or indirect. The latter comprise those effects mediated by the physicochemical state of the membrane bilayer, whereas direct modulation entails the more specific regulatory effects transduced via recognition sites on the target membrane protein. The nicotinic acetylcholine receptor (nAChR), the paradigm member of the pentameric ligand-gated ion channel (pLGIC) superfamily of rapid neurotransmitter receptors, is modulated by both mechanisms. Reciprocally, the nAChR protein exerts influence on its surrounding interstitial lipids. Folding, conformational equilibria, ligand binding, ion permeation, topography, and diffusion of the nAChR are modulated by membrane lipids. The knowledge gained from biophysical studies of this prototypic membrane protein can be applied to other neurotransmitter receptors and most other integral membrane proteins.

Development of High Hydrostatic Pressure Applied in Pathogen Inactivation for Plasma

High hydrostatic pressure has been used to inactivate pathogens in foods for decades. There is a great potential to adapt this technology to inactivate pathogens in plasma and derivatives. To better evaluate the potential of this method, pathogen inoculated plasma samples were pressurized under different pressure application modes and temperatures. The inactivation efficacy of pathogens and activities of plasma proteins were monitored after treatment. The CFUs of E.coli was examined as the indicator of the inactivation efficiency. The factor V and VIII were chosen as the indicator of the plasma function. Preliminary experiments identified optimized treatment conditions: 200-250MPa, with 5×1 minute multi-pulsed high pressure at near 0°C (ice-water bath). Under this conditions, the inactivation efficacy of EMCV was >8.5log. The CFUs of E. coli were reduced by 7.5log, B. cereus were 8log. However, PPV and S. aureus cannot be inactivated efficiently. The activities of factor II, VII, IX, X, XI, XII, fibrinogen, IgG, IgM stayed over 95% compared to untreated. Factor V and VIII activity was maintained at 46–63% and 77–82%, respectively.

Xerocytosis is caused by mutations that alter the kinetics of the mechanosensitive channel PIEZO1

Familial xerocytosis (HX) in humans is an autosomal disease that causes dehydration of red blood cells resulting in hemolytic anemia which has been traced to two individual mutations in the mechanosensitive ion channel, PIEZO1. Each mutation alters channel kinetics in ways that can explain the clinical presentation. Both mutations slowed inactivation and introduced a pronounced latency for activation. A conservative substitution of lysine for arginine (R2456K) eliminated inactivation and also slowed deactivation, indicating that this mutant's loss of charge is not responsible for HX. Fitting the current vs. pressure data to Boltzmann distributions showed that the half-activation pressure, P1/2, for M2225R was similar to that of WT, whereas mutations at position 2456 were left shifted. The absolute stress sensitivity was calibrated by cotransfection and comparison with MscL, a well-characterized mechanosensitive channel from bacteria that is driven by bilayer tension. The slope sensitivity of WT and mutant human PIEZO1 (hPIEZO1) was similar to that of MscL implying that the in-plane area increased markedly, by ∼6-20 nm(2) during opening. In addition to the behavior of individual channels, groups of hPIEZO1 channels could undergo simultaneous changes in kinetics including a loss of inactivation and a long (∼200 ms), silent latency for activation. These observations suggest that hPIEZO1 exists in spatial domains whose global properties can modify channel gating. The mutations that create HX affect cation fluxes in two ways: slow inactivation increases the cation flux, and the latency decreases it. These data provide a direct link between pathology and mechanosensitive channel dysfunction in nonsensory cells.

Blood rheology in marine mammals

The field of blood oxygen transport and delivery to tissues has been studied by comparative physiologists for many decades. Within this general area, the particular differences in oxygen delivery between marine and terrestrial mammals has focused mainly on oxygen supply differences and delivery to the tissues under low blood flow diving conditions. Yet, the study of the inherent flow properties of the blood itself (hemorheology) is rarely discussed when addressing diving. However, hemorheology is important to the study of marine mammals because of the critical nature of the oxygen stores that are carried in the blood during diving periods. This review focuses on the essential elements of hemorheology, how they are defined and on fundamental rheological applications to marine mammals. While the comparative rationale used throughout the review is much broader than the particular problems associated with diving, the basic concepts focus on how changes in the flow properties of whole blood would be critical to oxygen delivery during diving. This review introduces the reader to most of the major rheological concepts that are relevant to the unique and unusual aspects of the diving physiology of marine mammals.

Low background, pulsatile, in vitro flow circuit for modeling coronary implant thrombosis

We have developed an in vitro method for creating pulsatile flows to mimic coronary type flow patterns on a beat-to-beat basis. The flow is created by accelerating fluid loops about an axis, inducing relative wall motion. Using this technique, a variety of oscillating flow patterns can be generated and modulated. Such flow generation offers the potential to monitor sensitive, flow-dependent, biological parameters like thrombosis while minimizing background disturbances from pump action and circuit effects. We examined this potential by measuring the loop occlusion time for loops stented with stainless steel 7-9 NIR stents and stentless control loops.

Influence of barometric pressure on interleukin-1β secretion

Monocytes and macrophages are activated by various environmental challenges, including microorganisms, radiation, and pollutants. These cells release cytokines, such as interleukin (IL)-1β, that mediate physiological adaptations to stress. This study sought to define further the role of IL-1β in general adaptation to environmental stress by testing the hypothesis that high altitude (20,000 ft, 6,096 m) would stimulate IL-1β secretion from isolated human blood mononuclear cells. Cells from six young men (aged 22–26 yr) were divided into separate cultures incubated in either standard ambient conditions or in one of three test conditions, hypobaric hypoxia (simulating 20,000 ft), hypobaric normoxia (20,000 ft, O2supplemented), and normobaric hypoxia (10% O2). This design allowed differentiation between pressure-related vs. oxygen-related effects. Each subject made multiple blood donations in order that cells from all subjects were tested in all conditions. Contrary to the hypothesis, IL-1β secretion was not induced at simulated altitude in basal cell cultures. In lipopolysaccharide-stimulated cell cultures, exposure to altitude inhibited IL-1β secretion by ∼40%, and the inhibition was due to the change in pressure ( P = 0.039) rather than the change in oxygen. Secretion of other factors (IL-1 receptor antagonist and soluble IL-1 receptor type II) was not inhibited. Although these results are in opposition to the original hypothesis, they provide insight regarding adaptations necessary for hematopoiesis in response to high altitude and also provide a cellular rationale for the mountain sanatoriums of the 19th and early 20th centuries.

Pressure-mediated oligonucleotide transfection of rat and human cardiovascular tissues

The application of gene therapy to human disease is currently restricted by the relatively low efficiency and potential hazards of methods of oligonucleotide or gene delivery. Antisense or transcription factor decoy oligonucleotides have been shown to be effective at altering gene expression in cell culture expreriments, but their in vivo application is limited by the efficiency of cellular delivery, the intracellular stability of the compounds, and their duration of activity. We report herein the development of a highly efficient method for naked oligodeoxynucleotide (ODN) transfection into cardiovascular tissues by using controlled, nondistending pressure without the use of viral vectors, lipid formulations, or exposure to other adjunctive, potentially hazardous substances. In this study, we have documented the ability of ex vivo, pressure-mediated transfection to achieve nuclear localization of fluorescent (FITC)-labeled ODN in approximately 90% and 50% of cells in intact human saphenous vein and rat myocardium, respectively. We have further documented that pressure-mediated delivery of antisense ODN can functionally inhibit target gene expression in both of these tissues in a sequence-specific manner at the mRNA and protein levels. This oligonucleotide transfection system may represent a safe means of achieving the intraoperative genetic engineering of failure-resistant human bypass grafts and may provide an avenue for the genetic manipultation of cardiac allograft rejection, allograft vasculopathy, or other transplant diseases.

The transduction of very small hydrostatic pressures

This paper reviews experiments in which cells, subjected to hydrostatic pressures of 20 kPa or less, (micro-pressures), demonstrate a perturbation in growth and or metabolism. Similarly, the behavioural responses of aquatic animals (lacking an obvious compressible gas phase) to comparable pressures are reviewed. It may be shown that in both cases the effect of such very low hydrostatic pressures cannot be mediated through the thermodynamic mechanisms which are invoked for the effects of high hydrostatic pressure. The general conclusion is that cells probably respond to micro-pressures through a mechanical process. Differential compression of cellular structures is likely to cause shear and strain, leading to changes in enzyme and/or ion channel activity. If this conclusion is true then it raises a novel question about the involvement of 'micro-mechanical' effects in cells subjected to high hydrostatic pressure. The responses of aquatic animals to micro-pressures may be accounted for, using the model case of the crab, by the mechanical, bulk, compression of hair cells in the statocysts, the organ of balance. If this is true, it raises the interesting question of why the putative cellular mechanisms of micro-pressure transduction appear to have been superseded by the statocyst.