Small angle neutron scattering contrast variation reveals heterogeneities of interactions in protein gels.

We propose a quantitative approach to probe the spatial heterogeneities of interactions in macromolecular gels, based on a combination of small angle X-ray (SAXS) and neutrons (SANS) scattering. We investigate the structure of model gluten protein gels and show that the gels display radically different SAXS and SANS profiles when the solvent is (at least partially) deuterated. The detailed analysis of the SANS signal as a function of the solvent deuteration demonstrates heterogeneities of sample deuteration at different length scales. The progressive exchange between the protons (H) of the proteins and the deuteriums (D) of the solvent is inhomogeneous and 60 nm large zones that are enriched in H are evidenced. In addition, at low protein concentration, in the sol state, solvent deuteration induces a liquid/liquid phase separation. Complementary biochemical and structure analyses show that the denser protein phase is more protonated and specifically enriched in glutenin, the polymeric fraction of gluten proteins. These findings suggest that the presence of H-rich zones in gluten gels would arise from the preferential interaction of glutenin polymers through a tight network of non-exchangeable intermolecular hydrogen bonds.

[Does the sinoatrial node conduction time depend on heart rate?]. / Czy czas przewodzenia zatokowo-przedsionkowego zalezy od czestosci rytmu serca?

The informations about the dependence of sinoatrial conduction time (SACT) on heart rate (HR) are unequivocal. The aim of the study was to establish if such a dependence really exists. The study group comprised 24 patients (9 women and 15 men) aged 42-71 years, mean 55.8. All the patients presented atrial premature contractions of various etiology. No agents affecting heart electrophysiology were administered until the study was completed. In every patient SACT was estimated by means of the Strauss formula from the 24-hr ecg and from transoesophageal single impulse stimulation. SACT obtained from 24-hr ecg was 156.2 +/- 33.1 ms; whereas the one respectively, calculated from the transoesophageal stimulation was 119.0 +/- 21.0 ms. Despite a significant difference between the results (p less than 0.001), the SACT values obtained with both methods correlated well with each other (r = 0.712; p less than 0.01). The dependence of SACT on basic heart cycle length was observed in 9 pts during 24-h ecg (37.5%). Among these pts SACT was shortened with higher and lengthened with lower HR. In the remaining 15 pts this dependence didn't occur, neither it occurred in any patients examined with the single impulse stimulation. The results suggest that the dependence of SACT on HR is not a constant phenomenon and that it occurs only in a part of the examined population.

Thick collagen-based 3D matrices including growth factors to induce neurite outgrowth.

Designing synthetic microenvironments for cellular investigations is a very active area of research at the crossroads of cell biology and materials science. The present work describes the design and functionalization of a three-dimensional (3D) culture support dedicated to the study of neurite outgrowth from neural cells. It is based on a dense self-assembled collagen matrix stabilized by 100-nm-wide interconnected native fibrils without chemical crosslinking. The matrices were made suitable for cell manipulation and direct observation in confocal microscopy by anchoring them to traditional glass supports with a calibrated thickness of ∼50µm. The matrix composition can be readily adapted to specific neural cell types, notably by incorporating appropriate neurotrophic growth factors. Both PC-12 and SH-SY5Y lines respond to growth factors (nerve growth factor and brain-derived neurotrophic factor, respectively) impregnated and slowly released from the support. Significant neurite outgrowth is reported for a large proportion of cells, up to 66% for PC12 and 49% for SH-SY5Y. It is also shown that both growth factors can be chemically conjugated (EDC/NHS) throughout the matrix and yield similar proportions of cells with longer neurites (61% and 52%, respectively). Finally, neurite outgrowth was observed over several tens of microns within the 3D matrix, with both diffusing and immobilized growth factors.