Biomedical subjects

P Sens

Publications and source records attributed to P Sens.

6 recordsLinked to original sources

PubMed2003

Interactions between proteins bound to biomembranes.

We study a physical model for the interaction between general inclusions bound to fluid membranes that possess finite tension gamma, as well as the usual bending rigidity kappa. We are motivated by an interest in proteins bound to cell membranes that apply forces to these membranes, due to either entropic or direct chemical interactions. We find an exact analytic solution for the repulsive interaction between two similar circularly symmetric inclusions. This repulsion extends over length scales approximately sqrt[kappa/gamma] and contrasts with the membrane-mediated contact attraction for similar inclusions on tensionless membranes. For noncircularly symmetric inclusions we study the small, algebraically long-ranged, attractive contribution to the force that arises. We discuss the relevance of our results to biological phenomena, such as the budding of caveolae from cell membranes and the striations that are observed on their coats. These, and other, "gnarly buds" may prove fascinating to study further.

Biophysical Phenomena↗

PubMed2003

Hypereosinophilia-induced digital necrosis in a smoking patient.

Raynaud's phenomenon and digital necrosis of the fingers are rare complications of hypereosinophilia. We report a case of a smoking male who developed Raynaud's phenomenon and digital necrosis of the fingers associated with idiopathic hypereosinophilia with angiographically documented occlusion of small and medium arteries of the extremities. The eosinophils may play a thrombotic role in vascular pathology and eosinophil blood count should be checked when investigating patients with digital gangrene.

Adult↗

PubMed2000

Counterion release and electrostatic adsorption

The effective charge of a rigid polyelectrolyte (PE) approaching an oppositely charged surface is studied. The cases of a weak (annealed) and strongly charged PE with condensed counterions (such as DNA) are discussed. In the most interesting case of the adsorption onto a substrate of low dielectric constant (such as a lipid membrane or a mica sheet) the condensed counterions are not always released as the PE approaches the substrate, because of the major importance of the image-charge effect. For the adsorption onto a surface with freely moving charges, the image-charge effect becomes less important and full release is often expected.

Journal Article↗

PubMed1999

Inclusions on fluid membranes anchored to elastic media.

We model theoretically the effect of localized forces on a fluid membrane anchored to a uniform elastic medium. We use this as a simple model for the plasma membrane of a cell. The atomic force microscope (AFM) has been used to apply such forces, but large membrane perturbations occurring in vivo are also treated within the same framework. Inclusions of this nature may include cell junctions, filipodia, caveolae, and similar membrane invaginations. The breakdown of linear elastic response, as observed by AFM, is predicted to occur for forces as small as 10 pN. We estimate the position of this crossover and the subsequent nonlinear behavior and make encouraging quantitative comparison with experiments. Intrinsic membrane inclusions interact through their overlapping strain fields. For similar, point force-like inclusions at large separations, this yields an attractive potential that scales like the inverse of their separation. For membranes that are intrinsically stiff or under tension, the binding force between inclusions can depend on the properties of the membrane and may be large enough to induce aggregation of inclusions, as observed experimentally. For inclusions that fix the magnitude of the membrane deformation, rather than the applied force, we demonstrate the possibility of metastable states, corresponding to finite separations. Finally, we discuss briefly the case in which inclusions couple to the membrane in more complex ways, such as via a torque (twist). In such cases, the interaction scales like a higher power of the separation, depends on the orientation of the inclusions, and can have either sign.

Biophysical Phenomena↗

PubMed1999

Myocardial bridging as a cause of acute transient left heart dysfunction.

The significance of myocardial bridging is still a matter of debate, and although several reports have underlined its pathologic potential, myocardial bridging is often considered to be a benign phenomenon. We present here the case of a 63-year-old woman with a history of acute left heart failure and ECG evidence of ischemia, and whose primary abnormality on extensive workup was myocardial bridging. This case further underlines that myocardial bridging can lead to significant cardiac events.

Acute Disease↗

PubMed1989

[Attempt at diagnosis of hereditary spherocytosis using the ionophore valinomycin].

On the basis of former observations that erythrocytes of patients with hereditary spherocytosis (HS) exhibit a slighter K+ efflux under the influence of valinomycin and a diminished shrinking, the attempt was made to use this phenomenon in routine diagnostics. In pair comparison the findings already known could be proved impressively. However, obligatory limiting values which make it possible to dispense with giving statements of comparison could not be established. In this report the test is of limited value for haematological diagnostics.

Erythrocytes↗