Biomedical subjects

Monika Ritsch-Marte

Publications and source records attributed to Monika Ritsch-Marte.

8 recordsLinked to original sources

PubMed2006

Phagocytosis of human retinal pigment epithelial cells: evidence of a diurnal rhythm, involvement of the cytoskeleton and interference of antiviral drugs.

Retinal pigment epithelial (RPE) cells provide crucial functions for the maintenance of the retinal environment. We investigated the phagocytotic mechanisms of RPE cells evaluating the question whether particle uptake underlies a diurnal rhythm. Additionally, a possible connection of volume regulation and the phagocytotic function of RPE cells was studied. As antiviral nucleoside analogues influence cell-volume-regulating mechanisms, we tested several antiviral drugs. Cultured primary RPE cells and a permanent cell line (ARPE-19) were tested for uptake of europium-labeled microspheres quantified by time-resolved fluorometry. Cells were also exposed to cyclic illumination or continuous light and dark culture conditions. Inhibitors of cytoskeleton (microtubuli, actin) and osmotic swelling were also tested. Ingested FITC-labeled microparticles were found in phagosomes strongly associated which the cytoskeleton as they could not be easily moved by laser tweezer microscopy. Phagocytosis was observed predominately during dark intervals and was reduced by continuous light exposure. The diurnal rhythm of unsynchronized RPE cultures was abolished by microtubule inhibitors although no inhibition of overall particle uptake by cytoskeletal blockers was observed. Hypoosmotic swelling of RPE also decreased phagocytosis. Acyclovir was found inhibitory in ARPE-19 cells, whereas azidothymidine showed a protracted inhibiting activity on primary RPE cells and ganciclovir was inactive in both cell types. The presence of a diurnal rhythm also in culture indicates genetic determination of light-regulated particle uptake. This mechanism appears to be influenced by the regulation of cell volume and microtubule function. Inhibition of RPE function by antiviral drugs is a novel finding and in accordance with interferences of the tested drugs with cellular chloride channels described earlier. It may give a hint towards possible ocular side effects in the long-term use of nucleoside-analogous substances.

Actins↗

PubMed2006

Spiral interferogram analysis.

Interference microscopy using spatial Fourier filtering with a vortex phase element leads to interference fringes that are spirals rather than closed rings. Depressions and elevations in the optical thickness of the sample can be distinguished immediately by the sense of rotation of the spirals. This property allows an unambiguous reconstruction of the object's phase profile from one single interferogram. We investigate the theoretical background of "spiral interferometry" and suggest various demodulation techniques based on the processing of one single interferogram or multiple interferograms.

Journal Article↗

PubMed2005

Spiral interferometry.

We present a surprising modification of optical interferometry. A so-called spiral phase element in the beam path of a standard microscope results in an interferogram of phase samples, for which the interference fringes have the shape of spirals instead of closed contour lines as in traditional interferograms. This configuration overrides the basic problem of interferometry, i.e., that elevations and depressions cannot be distinguished. Therefore a complete sample profile can be reconstructed from a single exposure, promising, e.g., high-speed metrology with a single laser pulse. The method is easy to implement, it does not require a spatially separated reference beam, and it is optimally stable against environmental noise.

Journal Article↗

PubMed2005

Shadow effects in spiral phase contrast microscopy.

Recently it has been demonstrated that spatial filtering of images in microscopy with a spiral phase element in a Fourier plane of the optical path results in a strong edge enhancement of object structures. In principle the operation is isotropic, i.e., all phase edges of a sample object are highlighted simultaneously, independent of their local direction. However, here we demonstrate that the symmetry can be broken intentionally by controlling the phase of the central area of a spiral phase hologram, which is displayed at a computer controlled spatial light modulator. This produces an apparent shadow effect which can be rotated at video rate. The resulting relieflike impression of the sample topography with a longitudinal resolution in the subwavelength regime is demonstrated by imaging a standard low contrast test sample consisting of a human cheek cell.

Journal Article↗

PubMed2004

[Spatial and temporal control of ultrasonic fields via optoacoustic holography].

The present paper presents a new method for generating ultrasound, based on the interaction of laser-induced ultrasound generation and ultrasonic holography. An ultrasonic field generated in a water tank via the optoacoustic effect is spatially and temporally controlled: In order to produce defined ultrasonic frequencies in the MHz range, the laser pulses incident on a light-absorbing layer are modulated in time using an electro-optic modulator (EOM). Additionally, a high-resolution liquid crystal spatial light modulator (SLM) is used to imprint a pre-calculated phase front to the laser beam. A computer-generated binary hologram is also displayed at the SLM. The expanded laser beam projects the corresponding pattern to the plane absorptive layer in the water tank. The projection of specific patterns for the generation of ultrasonic beams resembles the use of, diffractive optical elements" in optics. Optical ultrasound generation with holographic steering is a flexible tool with promising numerous new applications in medical and technical ultrasound diagnostics.

Dose-Response Relationship, Radiation↗

PubMed2003

Ca2+ entry is essential for cell strain-induced lamellar body fusion in isolated rat type II pneumocytes.

Using a new equibiaxial strain device, we investigated strain-induced Ca2+ signals and their relation to lamellar body (LB) exocytosis in single rat alveolar type II (AT II) cells. The strain device allows observation of single cells while inducing strain to the entire substratum. AT II cells tolerated high strain amplitudes up to 45% increase in cell surface area (Delta CSA) without release of lactate dehydrogenase or ATP. Strain exceeding a threshold of approximately 8% Delta CSA resulted in a transient rise of the cytoplasmic Ca2+ concentration in some cells. Higher strain levels increased the fraction of Ca2+-responding cells. The occurrence of strain-induced Ca2+ signals depended on cell-cell contacts, because lone cells (i.e., cells without cell-cell contacts) did not exhibit Ca2+ signals. Above threshold, the amplitude of the Ca2+ signal as well as the number of stimulated LB fusions correlated well with the amplitude of strain. Furthermore, stimulated LB fusions occurred only in cells exhibiting a Ca2+ signal; 50 microM Gd3+ in the bath affected neither Ca2+ signals nor fusions. Intracellular Ca2+ release was triggered at higher strain amplitudes and inhibited by thapsigargin. Removal of bath Ca2+ completely inhibited Ca2+ signals and fusions. We conclude that strain of AT II cells stimulates a Ca2+ entry pathway that is highly sensitive to strain and a prerequisite for subsequent Ca2+ release. Both mechanisms result in a graded response of fusions to strain. Our data also allow us to introduce the term "effective strain" as the physiologically relevant portion of the strain amplitude.

Animals↗

PubMed2003

Mechanical forces impeding exocytotic surfactant release revealed by optical tweezers.

The release of surfactant from alveolar type II cells is essential to lower the surface tension in the lung and to facilitate inspiration. However, the factors controlling dispersal and diffusion of this hydrophobic material are still poorly understood. Here we report that release of surfactant from the fused vesicle, termed lamellar body (LB), resisted mechanical forces applied by optical tweezers: At constant trapping force, the probability to expand LB contents, i.e., to "pull" surfactant into the extracellular fluid, increased with time after LB fusion with the plasma membrane, consistent with slow fusion pore expansion in these cells. Elevations of the cytoplasmic Ca(2+) concentration ([Ca(2+)](c)) had a similar effect. Inasmuch as surfactant did not disintegrate in the extracellular space, this method permitted for the first time the determination of elastic and recoil properties of the macromolecular complex, yielding a spring constant of approximately 12.5 pN/ micro m. This is the first functional evidence that release of hydrophobic material is mechanically impeded and occurs in an "all-or-none" fashion. This mode of release is most probably the result of cohesive forces of surfactant, combined with adhesive forces and/or retaining forces exerted by a constrictive fusion pore acting as a regulated mechanical barrier, withstanding forces up to 160 pN. In independent experiments equiaxial strain was exerted on cells without optical tweezers. Strain facilitated surfactant release from preexisting fused vesicles, consistent with the view of mechanical impediments during the release process, which can be overcome by cell strain.

Animals↗

PubMed2002

In vitro investigation on the pH dependence of the absorption and fluorescence properties of the photosensitizer mTHPC.

Fluorescence excitation efficiency is of great importance for photodynamic diagnosis. Because usually a difference in the interstitial pH between normal and tumor tissue occurs, it is necessary to assess the impact of pH on the fluorescence emission intensity of the photosensitizer meta-tetrahydroxyphenylchlorin (mTHPC) in this context. The results obtained by in vitro fluorescence measurements clearly indicate that pH values below 6 lead to a significant decrease in the fluorescence intensity. In the physiological range of pH 6.5-7.2, however, no pH dependence was found. Besides the decrease in the fluorescence intensity of mTHPC for pH < 6, changes in the spectral shape of the absorption were found. These changes can be utilized for "dual-wavelength ratio imaging," using mTHPC as a pH-sensitive indicator with the excitation pair 405 nm/436 nm in the range of pH 3.5-6.

Hydrogen-Ion Concentration↗