Atrial natriuretic peptide (ANP)-granules: ultrastructure, morphometry and function

The atrial granules containing the peptide hormone, Atrial natriuretic peptide (ANP) are present in the four regions of the atrial-auricular complex (two atria and two auricles). ANP-immunoreactivity was detected in all granules from the four regions. Ultrastructurally, atrial myocytes show the presence of very electron dense granules, with sparsely granular and homogeneous content, coated with a double membrane. The number of granules is greatest in the right atrium followed by the left atrium and left auricle and right auricle, in thisorder. The diameter of granules in the cardiocytes is significantly largest in the right atrium and reduced via the left auricle to the left atrium and right auricle. These data lead to suppose that the right atrium is the one that most synthesizes and stores the ANP. The number of ANP-granules is influenced by several physiological conditions: temperature, dehydration and nutritional condition. The main physiological stimulus for increased ANP release is the atrial muscle stretch, which normally occurs when extra cellular fluid volume or blood volume is elevated. The ANP is eliminated through the atrial myocytes, via exocytosis. Granule content is released into the extra-cellular space (extrusion). The ANP causes diuresis, natriuresis,vasodilatation and depression of blood pressure. It is also involved in the modification of the waterelectrolyte balance

Electrostatic response of hydrophobic surface measured by atomic force microscopy

The arrangement of water molecules at aqueous interfaces is an important question in material and biological sciences. We have measured the force acting on neutral tips as a function of the distance to hydrophobic silicon surfaces and cetyltrimethylammonium bromide monolayers covering mica surfaces in aqueous solutions. The unusually large magnitude of this force is attributed to an electrostatic response of the aqueous fluid structure (hydration layer) which is generated by the reorientation of water molecular dipoles. The exchange of a volume of this region with a dielectric permittivity (epsilon(int)) by the tip with a dielectric permittivity (epsilon(tip)) is responsible for the tip attraction when it is immersed in the polarization (hydration) layer. Variable permittivity profiles starting at epsilonapproximate to11 at the interface and increasing to epsilon=80 about 10 nm from hydrophobic silicon surfaces and about 50 nm from cetyltrimethylammonium bromide monolayer covering mica surfaces were measured. (C) 2003 American Institute of Physics.8271126112

Molecular arrangements of self-assembled surfactant films: Characterization from atomic force microscopy data

The adsorbed surfactant film molecular arrangement with thickness of similar to5 nm is determined by measurements of the film dielectric permittivity. Before the advent of atomic force microscopy the dielectric permittivity was a macroscopic parameter, appropriate only for describing uniform environments since its profile was difficult to measure for local intermolecular interactions and its spatial distribution was frequently settled without experimental justification. Here, we show that atomic force microscopy made it possible to measure the dielectric permittivity profile in a scale below 5 nm for adsorbed layers of self-assembled surfactant films in water. The measured values of the film's dielectric permittivity and the film's thickness determine the compactness of the adsorbed film and consequently the presence of water molecules in the film and the conformal structure of the adsorbed molecules.683

Imaging of soft structures: Dependence of contrast in atomic force microscopy images on the force applied by the tip

Forces acting on atomic force microscope tips during scanning of films of ionic surfactant molecules adsorbed from aqueous solutions onto hydrophilic substrates are measured. Near critical micellar concentration images of mica substrates show aggregate regions at the interface. Force versus distance curves indicate that aggregates are the thickest adsorbed structures on the substrate. However, topographic images registered at low scanning speed (15 mu m/s) show that these aggregates appear as holes, consequently observed as inverted in contrast images, Tn atomic force microscope imaging of soft structures such as surfactants or biological material, inverted images may be observed when the tip penetrates the scanned layers. This penetration can be adjusted by changing the force applied by the tip, which results in different images. In order to obtain the conventional atomic force microscope contrast in scanned images the applied force set point is determined by the analysis of the force versus distance curves. (C) 2000 American Vacuum Society. [S0734-211X(00)11803-7].1831144115

Dielectric exchange-force effect on the rupture force of adsorbed bilayers of self-assembled surfactant films

We measured and formulated dielectric exchange forces between adsorbed layers of self-assembled surfactant films and atomic-force microscope tips in water. The dielectric exchange-force model is in agreement with the observation that the surfactant-layer rupture forces (tip-applied force necessary to obtain tip/substrate contact) are smaller in the thickest layers, where the compactness of the adsorbed film results in the smallest values of the dielectric permittivity. Within experimental accuracy, a dielectric permittivity value of similar to4 for bilayers and of similar to 36 for monolayers is found. (C) 2001 American Institute of Physics.78203064306

Interfacial water dielectric-permittivity-profile measurements using atomic force microscopy

The arrangement of water molecules at charged aqueous interfaces is an important question in biology, electrochemistry, and geochemistry. Theoretical studies suggest that the molecules become arranged in several layers adjacent to a solid interface. Using atomic force microscopy we have measured the water dielectric-permittivity profile perpendicular to mica surfaces. The measured variable permittivity profile starting at epsilon approximate to4 at the interface and increasing to epsilon =80 about 10 nm from the surface suggests a reorientation of water molecule dipoles in the presence of the mica interfacial charge.641

Atomic scale patterns formed during surface scanning by atomic force microscopy tips

In this work, tip sliding at the water/substrate interfacial region was used to investigate the pattern observed during image acquisition with atomic resolution in atomic force microscopy. The process responsible for the pattern formation is the oscillatory movement of the tip in the direction that is normal to scanning induced by a change in the water interfacial dielectric permittivity from epsilon approximate to 4 at the interface to epsilon approximate to 80 (bulk value) that results in a variation of the measured force acting on the tip of approximate to 30 pN. (c) 2006 American Institute of Physics.892

Magnetic force images of nanomagnetic domains taken with platinum-coated tips

This article deals with magnetic force microscope images of nanosized domains in Co-coated films made by Pt-coated tips as well as micromagnetic images of data tracks written in recording media. Pt-coated tips have improved image delineation of the magnetic field distribution compared to images obtained by Co-coated hard magnetic tips. The force acting on Pt-coated tips in the magnetic field of the substrate was modeled assuming a paramagnetic tip. Due to the ferromagnetic nature of the interaction between the tip and substrate the spatial resolution of hard magnetic tips was shown to be inadequate to measure details of the features of nanosized domains. A comparison of the magnetic images made by Pt-coated tips with topographic images shows that magnetic domains resist thermal erasure at ambient temperature when they are formed of eight metallic grains. (C) 2003 American Institute of Physics.94162663

A Mitochondrial DNA Phylogeny Indicates Close Relationships between Populations of Lutzomyia whitmani (Diptera: Psychodidae, Phlebotominae) from the Rain-forest Regions of Amazônia and Northeast Brazil

Phylogenetic analysis of all 31 described mitochondrial (cytochrome b) haplotypes of Lutzomyia whitmani demonstrated that new material from the State of Rondônia, in southwest Amazônia, forms a clade within a lineage found only in the rain-forest regions of Brazil. This rain-forest lineage also contains two other clades of haplotypes, one from eastern Amazônia and one from the Atlantic forest zone of northeast Brazil (including the type locality of the species in Ilhéus, State of Bahia). These findings do not favour recognizing two allopatric cryptic species of L. whitmani, one associated with the silvatic transmission of Leishmania shawi in southeast Amazônia and the other with the peridomestic transmission of Le. braziliensis in northeast Brazil. Instead, they suggest that there is (or has been in the recent past) a continuum of inter-breeding populations of L. whitmani in the rain-forest regions of Brazil