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Biomedical subjects

Manfred Radmacher

Publications and source records attributed to Manfred Radmacher.

6 recordsLinked to original sources
PubMed2006

Direct measurement of the lamellipodial protrusive force in a migrating cell.

There has been a great deal of interest in the mechanism of lamellipodial protrusion (Pollard, T., and G. Borisy. 2003. Cell. 112:453-465). However, one of this mechanism's endpoints, the force of protrusion, has never been directly measured. We place an atomic force microscopy cantilever in the path of a migrating keratocyte. The deflection of the cantilever, which occurs over a period of approximately 10 s, provides a direct measure of the force exerted by the lamellipodial leading edge. Stall forces are consistent with approximately 100 polymerizing actin filaments per micrometer of the leading edge, each working as an elastic Brownian ratchet and generating a force of several piconewtons. However, the force-velocity curves obtained from this measurement, in which velocity drops sharply under very small loads, is not sensitive to low loading forces, and finally stalls rapidly at large loads, are not consistent with current theoretical models for the actin polymerization force. Rather, the curves indicate that the protrusive force generation is a complex multiphase process involving actin and adhesion dynamics.

Actin Cytoskeleton↗
PubMed2005

Influence of myosin II activity on stiffness of fibroblast cells.

Myosin II is responsible for establishing cytoskeleton tension within eukaryotic cells. We used an atomic force microscope to quantify the cells mechanical properties as a function of myosin activity. In two fibroblast cell lines, the elastic modulus of the cytoskeleton decrease by a factor of 3-5 regardless of location and cell type after inhibition of myosin II light chain kinase. We used two different inhibitors (BDM and ML-7) and observed the effects on two different fibroblast cell lines (3T3 and NRK). The cells stopped migration, retracted their lamellipodia, and softened by a factor of 3 in peripheral and in nuclear regions. The observed effect was concentration dependent. Application of the inhibitor at very low concentration had no effect on morphology or mechanical properties, whereas application of high concentration was usually lethal. At an intermediate range of concentrations, retraction of lamellipodia and softening of cells occurred, from which the cells recovered within an hour.

Animals↗
PubMed2005

Evidence for a highly elastic shell-core organization of cochlear outer hair cells by local membrane indentation.

Cochlear outer hair cells (OHCs) are thought to play an essential role in the high sensitivity and sharp frequency selectivity of the hearing organ by generating forces that amplify the vibrations of this organ at frequencies up to several tens of kHz. This tuning process depends on the mechanical properties of the cochlear partition, which OHC activity has been proposed to modulate on a cycle-by-cycle basis. OHCs have a specialized shell-core ultrastructure believed to be important for the mechanics of these cells and for their unique electromotility properties. Here we use atomic force microscopy to investigate the mechanical properties of isolated living OHCs and to show that indentation mechanics of their membrane is consistent with a shell-core organization. Indentations of OHCs are also found to be highly nonhysteretic at deformation rates of more than 40 microm/s, which suggests the OHC lateral wall is a highly elastic structure, with little viscous dissipation, as would appear to be required in view of the very rapid changes in shape and mechanics OHCs are believed to undergo in vivo.

Animals↗
PubMed2005

Enzyme-assisted nanolithography.

We have chemically immobilized alkaline phosphatase molecules onto the apex of a tip of an atomic force microscope. When the substrate BCIP is dephosphorylated by alkaline phosphatase, it will precipitate in the presence of NBT. By bringing the tip in the vicinity of a suitable sample, we could locally deposit this complex on the sample. Thus we combined the activity of an enzyme with the accuracy in positioning a tip in scanning probe microscopy to demonstrate a novel technique referred to as enzyme-assisted nanolithography. By use of other enzymes, this method will open the possibility to chemically modify surfaces on a nanometer scale.

Alkaline Phosphatase↗
PubMed2002

Measuring the elastic properties of living cells by the atomic force microscope.

In this chapter I discussed the possibility of measuring elastic properties of living cells by AFM. One reason for using the AFM for this purpose is its ability to both measure locally the mechanics of a cell and to distinguish different regions of the cell. Since the AFM can be operated under physiological conditions cellular processes can be followed, for example, cytokinesis and the investigation of the migration of cells.

Actins↗